| Message ID | 20201021225737.739-1-digetx@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v1] ARM: vfp: Use long jump to fix THUMB2 kernel compilation error | expand |
On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > The vfp_kmode_exception() function now is unreachable using relative > branching in THUMB2 kernel configuration, resulting in a "relocation > truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > linker error. Let's use long jump in order to fix the issue. Eek. Is this with gcc or clang? > > Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? That commit may have implicitly moved the location of .vfp11_veneer, though I thought I had chosen the correct position. > Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > --- > arch/arm/vfp/vfphw.S | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > index 4fcff9f59947..6e2b29f0c48d 100644 > --- a/arch/arm/vfp/vfphw.S > +++ b/arch/arm/vfp/vfphw.S > @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > and r3, r3, #MODE_MASK @ are supported in kernel mode > teq r3, #USR_MODE > - bne vfp_kmode_exception @ Returns through lr > + ldr r1, =vfp_kmode_exception > + bxne r1 @ Returns through lr > > VFPFMRX r1, FPEXC @ Is the VFP enabled? > DBGSTR1 "fpexc %08x", r1 This seems like a workaround though? I suspect the vfp11_veneer needs moving?
22.10.2020 02:40, Kees Cook пишет: > On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: >> The vfp_kmode_exception() function now is unreachable using relative >> branching in THUMB2 kernel configuration, resulting in a "relocation >> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" >> linker error. Let's use long jump in order to fix the issue. > > Eek. Is this with gcc or clang? GCC 9.3.0 >> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > That commit may have implicitly moved the location of .vfp11_veneer, > though I thought I had chosen the correct position. I re-checked that the fixes tag is correct. >> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> >> --- >> arch/arm/vfp/vfphw.S | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S >> index 4fcff9f59947..6e2b29f0c48d 100644 >> --- a/arch/arm/vfp/vfphw.S >> +++ b/arch/arm/vfp/vfphw.S >> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) >> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions >> and r3, r3, #MODE_MASK @ are supported in kernel mode >> teq r3, #USR_MODE >> - bne vfp_kmode_exception @ Returns through lr >> + ldr r1, =vfp_kmode_exception >> + bxne r1 @ Returns through lr >> >> VFPFMRX r1, FPEXC @ Is the VFP enabled? >> DBGSTR1 "fpexc %08x", r1 > > This seems like a workaround though? I suspect the vfp11_veneer needs > moving? > I don't know where it needs to be moved. Please feel free to make a patch if you have a better idea, I'll be glad to test it.
On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > 22.10.2020 02:40, Kees Cook пишет: > > On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > >> The vfp_kmode_exception() function now is unreachable using relative > >> branching in THUMB2 kernel configuration, resulting in a "relocation > >> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > >> linker error. Let's use long jump in order to fix the issue. > > > > Eek. Is this with gcc or clang? > > GCC 9.3.0 > > >> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > > > Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > That commit may have implicitly moved the location of .vfp11_veneer, > > though I thought I had chosen the correct position. > > I re-checked that the fixes tag is correct. > > >> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > >> --- > >> arch/arm/vfp/vfphw.S | 3 ++- > >> 1 file changed, 2 insertions(+), 1 deletion(-) > >> > >> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > >> index 4fcff9f59947..6e2b29f0c48d 100644 > >> --- a/arch/arm/vfp/vfphw.S > >> +++ b/arch/arm/vfp/vfphw.S > >> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > >> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > >> and r3, r3, #MODE_MASK @ are supported in kernel mode > >> teq r3, #USR_MODE > >> - bne vfp_kmode_exception @ Returns through lr > >> + ldr r1, =vfp_kmode_exception > >> + bxne r1 @ Returns through lr > >> > >> VFPFMRX r1, FPEXC @ Is the VFP enabled? > >> DBGSTR1 "fpexc %08x", r1 > > > > This seems like a workaround though? I suspect the vfp11_veneer needs > > moving? > > > > I don't know where it needs to be moved. Please feel free to make a > patch if you have a better idea, I'll be glad to test it. I might have just been distracted by the common "vfp" prefix. It's possible that the text section shuffling just ended up being very large, so probably this patch is right then!
On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > > On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > 22.10.2020 02:40, Kees Cook пишет: > > > On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > >> The vfp_kmode_exception() function now is unreachable using relative > > >> branching in THUMB2 kernel configuration, resulting in a "relocation > > >> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > >> linker error. Let's use long jump in order to fix the issue. > > > > > > Eek. Is this with gcc or clang? > > > > GCC 9.3.0 > > > > >> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > > > > > Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > > That commit may have implicitly moved the location of .vfp11_veneer, > > > though I thought I had chosen the correct position. > > > > I re-checked that the fixes tag is correct. > > > > >> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > >> --- > > >> arch/arm/vfp/vfphw.S | 3 ++- > > >> 1 file changed, 2 insertions(+), 1 deletion(-) > > >> > > >> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > >> index 4fcff9f59947..6e2b29f0c48d 100644 > > >> --- a/arch/arm/vfp/vfphw.S > > >> +++ b/arch/arm/vfp/vfphw.S > > >> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > >> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > >> and r3, r3, #MODE_MASK @ are supported in kernel mode > > >> teq r3, #USR_MODE > > >> - bne vfp_kmode_exception @ Returns through lr > > >> + ldr r1, =vfp_kmode_exception > > >> + bxne r1 @ Returns through lr > > >> > > >> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > >> DBGSTR1 "fpexc %08x", r1 > > > > > > This seems like a workaround though? I suspect the vfp11_veneer needs > > > moving? > > > > > > > I don't know where it needs to be moved. Please feel free to make a > > patch if you have a better idea, I'll be glad to test it. > > I might have just been distracted by the common "vfp" prefix. It's > possible that the text section shuffling just ended up being very large, > so probably this patch is right then! > I already sent a fix for this issue: https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1
On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > The vfp_kmode_exception() function now is unreachable using relative > branching in THUMB2 kernel configuration, resulting in a "relocation > truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > linker error. Let's use long jump in order to fix the issue. > > Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > Signed-off-by: Dmitry Osipenko <digetx@gmail.com> I guess the problem is that vfp_support_entry is in .text which tends to be at the beginning of the text section, but vfp_kmode_exception is in something like .text.vfp_kmode_exception ? Would it be an idea just to change the section name that stuff like vfp_support_entry ends up in, rather than making the code less efficient?
22.10.2020 17:57, Russell King - ARM Linux admin пишет: > On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: >> The vfp_kmode_exception() function now is unreachable using relative >> branching in THUMB2 kernel configuration, resulting in a "relocation >> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" >> linker error. Let's use long jump in order to fix the issue. >> >> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") >> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > I guess the problem is that vfp_support_entry is in .text which tends > to be at the beginning of the text section, but vfp_kmode_exception > is in something like .text.vfp_kmode_exception ? Indeed, vfp_support_entry is at beginning of .text, while vfp_kmode_exception is near the end. > Would it be an idea just to change the section name that stuff like > vfp_support_entry ends up in, rather than making the code less > efficient? > This works: diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S index 4fcff9f59947..65f0a2ef3613 100644 --- a/arch/arm/vfp/vfphw.S +++ b/arch/arm/vfp/vfphw.S @@ -65,6 +65,7 @@ #endif .endm + .pushsection .vfp11_veneer, "ax" @ VFP hardware support entry point. @ diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c index 8c9e7f9f0277..30b83b191174 100644 --- a/arch/arm/vfp/vfpmodule.c +++ b/arch/arm/vfp/vfpmodule.c @@ -642,7 +642,7 @@ static int vfp_starting_cpu(unsigned int unused) return 0; } -void vfp_kmode_exception(void) +void __section(".vfp11_veneer") vfp_kmode_exception(void) { /* * If we reach this point, a floating point exception has been raised
22.10.2020 10:06, Ard Biesheuvel пишет: > On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: >> >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: >>> 22.10.2020 02:40, Kees Cook пишет: >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: >>>>> The vfp_kmode_exception() function now is unreachable using relative >>>>> branching in THUMB2 kernel configuration, resulting in a "relocation >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" >>>>> linker error. Let's use long jump in order to fix the issue. >>>> >>>> Eek. Is this with gcc or clang? >>> >>> GCC 9.3.0 >>> >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") >>>> >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? >>>> That commit may have implicitly moved the location of .vfp11_veneer, >>>> though I thought I had chosen the correct position. >>> >>> I re-checked that the fixes tag is correct. >>> >>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> >>>>> --- >>>>> arch/arm/vfp/vfphw.S | 3 ++- >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S >>>>> index 4fcff9f59947..6e2b29f0c48d 100644 >>>>> --- a/arch/arm/vfp/vfphw.S >>>>> +++ b/arch/arm/vfp/vfphw.S >>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) >>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode >>>>> teq r3, #USR_MODE >>>>> - bne vfp_kmode_exception @ Returns through lr >>>>> + ldr r1, =vfp_kmode_exception >>>>> + bxne r1 @ Returns through lr >>>>> >>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? >>>>> DBGSTR1 "fpexc %08x", r1 >>>> >>>> This seems like a workaround though? I suspect the vfp11_veneer needs >>>> moving? >>>> >>> >>> I don't know where it needs to be moved. Please feel free to make a >>> patch if you have a better idea, I'll be glad to test it. >> >> I might have just been distracted by the common "vfp" prefix. It's >> possible that the text section shuffling just ended up being very large, >> so probably this patch is right then! >> > > I already sent a fix for this issue: > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > The offending commit contains stable tag, so I assume that fixes tag is mandatory. Yours patch misses the fixes tag.
On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > > 22.10.2020 10:06, Ard Biesheuvel пишет: > > On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > >> > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > >>> 22.10.2020 02:40, Kees Cook пишет: > >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > >>>>> The vfp_kmode_exception() function now is unreachable using relative > >>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > >>>>> linker error. Let's use long jump in order to fix the issue. > >>>> > >>>> Eek. Is this with gcc or clang? > >>> > >>> GCC 9.3.0 > >>> > >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > >>>> > >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > >>>> That commit may have implicitly moved the location of .vfp11_veneer, > >>>> though I thought I had chosen the correct position. > >>> > >>> I re-checked that the fixes tag is correct. > >>> > >>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > >>>>> --- > >>>>> arch/arm/vfp/vfphw.S | 3 ++- > >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > >>>>> > >>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > >>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > >>>>> --- a/arch/arm/vfp/vfphw.S > >>>>> +++ b/arch/arm/vfp/vfphw.S > >>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > >>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > >>>>> teq r3, #USR_MODE > >>>>> - bne vfp_kmode_exception @ Returns through lr > >>>>> + ldr r1, =vfp_kmode_exception > >>>>> + bxne r1 @ Returns through lr > >>>>> > >>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > >>>>> DBGSTR1 "fpexc %08x", r1 > >>>> > >>>> This seems like a workaround though? I suspect the vfp11_veneer needs > >>>> moving? > >>>> > >>> > >>> I don't know where it needs to be moved. Please feel free to make a > >>> patch if you have a better idea, I'll be glad to test it. > >> > >> I might have just been distracted by the common "vfp" prefix. It's > >> possible that the text section shuffling just ended up being very large, > >> so probably this patch is right then! > >> > > > > I already sent a fix for this issue: > > > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > > The offending commit contains stable tag, so I assume that fixes tag is > mandatory. Yours patch misses the fixes tag. Russell, mind adding that? Or would you like me to update the patch in the patch system?
On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > > > > 22.10.2020 10:06, Ard Biesheuvel пишет: > > > On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > > >> > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > >>> 22.10.2020 02:40, Kees Cook пишет: > > >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > >>>>> The vfp_kmode_exception() function now is unreachable using relative > > >>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > >>>>> linker error. Let's use long jump in order to fix the issue. > > >>>> > > >>>> Eek. Is this with gcc or clang? > > >>> > > >>> GCC 9.3.0 > > >>> > > >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > >>>> > > >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > >>>> That commit may have implicitly moved the location of .vfp11_veneer, > > >>>> though I thought I had chosen the correct position. > > >>> > > >>> I re-checked that the fixes tag is correct. > > >>> > > >>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > >>>>> --- > > >>>>> arch/arm/vfp/vfphw.S | 3 ++- > > >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > >>>>> > > >>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > >>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > >>>>> --- a/arch/arm/vfp/vfphw.S > > >>>>> +++ b/arch/arm/vfp/vfphw.S > > >>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > >>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > >>>>> teq r3, #USR_MODE > > >>>>> - bne vfp_kmode_exception @ Returns through lr > > >>>>> + ldr r1, =vfp_kmode_exception > > >>>>> + bxne r1 @ Returns through lr > > >>>>> > > >>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > >>>>> DBGSTR1 "fpexc %08x", r1 > > >>>> > > >>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > >>>> moving? > > >>>> > > >>> > > >>> I don't know where it needs to be moved. Please feel free to make a > > >>> patch if you have a better idea, I'll be glad to test it. > > >> > > >> I might have just been distracted by the common "vfp" prefix. It's > > >> possible that the text section shuffling just ended up being very large, > > >> so probably this patch is right then! > > >> > > > > > > I already sent a fix for this issue: > > > > > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > > > > > The offending commit contains stable tag, so I assume that fixes tag is > > mandatory. Yours patch misses the fixes tag. > > Russell, mind adding that? Or would you like me to update the patch in > the patch system? Rather than adding the IT, I'm suggesting that we solve it a different way - ensuring that the two bits of code are co-located. There's no reason for them to be separated, and the assembly code entry point is already called indirectly. The problem is the assembly ends up in the .text section which ends up at the start of the binary, but depending on the compiler, functions in .c files end up in their own sections. It would be good if, as Dmitry has shown that it is indeed possible, to have them co-located.
On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin <linux@armlinux.org.uk> wrote: > > On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > > On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > > > > > > 22.10.2020 10:06, Ard Biesheuvel пишет: > > > > On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > > > >> > > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > > >>> 22.10.2020 02:40, Kees Cook пишет: > > > >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > > >>>>> The vfp_kmode_exception() function now is unreachable using relative > > > >>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > > >>>>> linker error. Let's use long jump in order to fix the issue. > > > >>>> > > > >>>> Eek. Is this with gcc or clang? > > > >>> > > > >>> GCC 9.3.0 > > > >>> > > > >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > > >>>> > > > >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > > >>>> That commit may have implicitly moved the location of .vfp11_veneer, > > > >>>> though I thought I had chosen the correct position. > > > >>> > > > >>> I re-checked that the fixes tag is correct. > > > >>> > > > >>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > > >>>>> --- > > > >>>>> arch/arm/vfp/vfphw.S | 3 ++- > > > >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > > >>>>> > > > >>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > > >>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > > >>>>> --- a/arch/arm/vfp/vfphw.S > > > >>>>> +++ b/arch/arm/vfp/vfphw.S > > > >>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > > >>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > > >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > > >>>>> teq r3, #USR_MODE > > > >>>>> - bne vfp_kmode_exception @ Returns through lr > > > >>>>> + ldr r1, =vfp_kmode_exception > > > >>>>> + bxne r1 @ Returns through lr > > > >>>>> > > > >>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > > >>>>> DBGSTR1 "fpexc %08x", r1 > > > >>>> > > > >>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > > >>>> moving? > > > >>>> > > > >>> > > > >>> I don't know where it needs to be moved. Please feel free to make a > > > >>> patch if you have a better idea, I'll be glad to test it. > > > >> > > > >> I might have just been distracted by the common "vfp" prefix. It's > > > >> possible that the text section shuffling just ended up being very large, > > > >> so probably this patch is right then! > > > >> > > > > > > > > I already sent a fix for this issue: > > > > > > > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > > > > > > > > The offending commit contains stable tag, so I assume that fixes tag is > > > mandatory. Yours patch misses the fixes tag. > > > > Russell, mind adding that? Or would you like me to update the patch in > > the patch system? > > Rather than adding the IT, I'm suggesting that we solve it a different > way - ensuring that the two bits of code are co-located. There's no > reason for them to be separated, and the assembly code entry point is > already called indirectly. > > The problem is the assembly ends up in the .text section which ends up > at the start of the binary, but depending on the compiler, functions > in .c files end up in their own sections. It would be good if, as > Dmitry has shown that it is indeed possible, to have them co-located. > Why is that better? I provided a minimal fix which has zero impact on ARM builds, and minimal impact on Thumb2 builds, given that it retains the exact same semantics as before, but using a different opcode. R_ARM_THM_JUMP19 only has -/+ 1 MB range, i.e., smaller than the size of .text, and so using it for calls to external symbols is still going to be risky, unless we create a completely separate code section for VFP related routines. So we may need the IT instruction anyway, at which point we don't need anything more.
On Thu, Oct 22, 2020 at 06:20:40PM +0200, Ard Biesheuvel wrote: > On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin > <linux@armlinux.org.uk> wrote: > > > > On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > > > On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > > > > > > > > 22.10.2020 10:06, Ard Biesheuvel пишет: > > > > > On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > > > > >> > > > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > > > >>> 22.10.2020 02:40, Kees Cook пишет: > > > > >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > > > >>>>> The vfp_kmode_exception() function now is unreachable using relative > > > > >>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > > > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > > > >>>>> linker error. Let's use long jump in order to fix the issue. > > > > >>>> > > > > >>>> Eek. Is this with gcc or clang? > > > > >>> > > > > >>> GCC 9.3.0 > > > > >>> > > > > >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > > > >>>> > > > > >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > > > >>>> That commit may have implicitly moved the location of .vfp11_veneer, > > > > >>>> though I thought I had chosen the correct position. > > > > >>> > > > > >>> I re-checked that the fixes tag is correct. > > > > >>> > > > > >>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > > > >>>>> --- > > > > >>>>> arch/arm/vfp/vfphw.S | 3 ++- > > > > >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > > > >>>>> > > > > >>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > > > >>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > > > >>>>> --- a/arch/arm/vfp/vfphw.S > > > > >>>>> +++ b/arch/arm/vfp/vfphw.S > > > > >>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > > > >>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > > > >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > > > >>>>> teq r3, #USR_MODE > > > > >>>>> - bne vfp_kmode_exception @ Returns through lr > > > > >>>>> + ldr r1, =vfp_kmode_exception > > > > >>>>> + bxne r1 @ Returns through lr > > > > >>>>> > > > > >>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > > > >>>>> DBGSTR1 "fpexc %08x", r1 > > > > >>>> > > > > >>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > > > >>>> moving? > > > > >>>> > > > > >>> > > > > >>> I don't know where it needs to be moved. Please feel free to make a > > > > >>> patch if you have a better idea, I'll be glad to test it. > > > > >> > > > > >> I might have just been distracted by the common "vfp" prefix. It's > > > > >> possible that the text section shuffling just ended up being very large, > > > > >> so probably this patch is right then! > > > > >> > > > > > > > > > > I already sent a fix for this issue: > > > > > > > > > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > > > > > > > > > > > The offending commit contains stable tag, so I assume that fixes tag is > > > > mandatory. Yours patch misses the fixes tag. > > > > > > Russell, mind adding that? Or would you like me to update the patch in > > > the patch system? > > > > Rather than adding the IT, I'm suggesting that we solve it a different > > way - ensuring that the two bits of code are co-located. There's no > > reason for them to be separated, and the assembly code entry point is > > already called indirectly. > > > > The problem is the assembly ends up in the .text section which ends up > > at the start of the binary, but depending on the compiler, functions > > in .c files end up in their own sections. It would be good if, as > > Dmitry has shown that it is indeed possible, to have them co-located. > > Why is that better? I provided a minimal fix which has zero impact on > ARM builds, and minimal impact on Thumb2 builds, given that it retains > the exact same semantics as before, but using a different opcode. I think you just described the reason there. Why should we force everything to use a different opcode when a short jump _should_ suffice? Your patch may be a single line, but it has a slightly greater impact than the alternative two line solution.
On Thu, 22 Oct 2020 at 18:23, Russell King - ARM Linux admin <linux@armlinux.org.uk> wrote: > > On Thu, Oct 22, 2020 at 06:20:40PM +0200, Ard Biesheuvel wrote: > > On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin > > <linux@armlinux.org.uk> wrote: > > > > > > On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > > > > On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > > > > > > > > > > 22.10.2020 10:06, Ard Biesheuvel пишет: > > > > > > On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > > > > > >> > > > > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > > > > >>> 22.10.2020 02:40, Kees Cook пишет: > > > > > >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > > > > >>>>> The vfp_kmode_exception() function now is unreachable using relative > > > > > >>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > > > > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > > > > >>>>> linker error. Let's use long jump in order to fix the issue. > > > > > >>>> > > > > > >>>> Eek. Is this with gcc or clang? > > > > > >>> > > > > > >>> GCC 9.3.0 > > > > > >>> > > > > > >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > > > > >>>> > > > > > >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > > > > >>>> That commit may have implicitly moved the location of .vfp11_veneer, > > > > > >>>> though I thought I had chosen the correct position. > > > > > >>> > > > > > >>> I re-checked that the fixes tag is correct. > > > > > >>> > > > > > >>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > > > > >>>>> --- > > > > > >>>>> arch/arm/vfp/vfphw.S | 3 ++- > > > > > >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > >>>>> > > > > > >>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > > > > >>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > > > > >>>>> --- a/arch/arm/vfp/vfphw.S > > > > > >>>>> +++ b/arch/arm/vfp/vfphw.S > > > > > >>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > > > > >>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > > > > >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > > > > >>>>> teq r3, #USR_MODE > > > > > >>>>> - bne vfp_kmode_exception @ Returns through lr > > > > > >>>>> + ldr r1, =vfp_kmode_exception > > > > > >>>>> + bxne r1 @ Returns through lr > > > > > >>>>> > > > > > >>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > > > > >>>>> DBGSTR1 "fpexc %08x", r1 > > > > > >>>> > > > > > >>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > > > > >>>> moving? > > > > > >>>> > > > > > >>> > > > > > >>> I don't know where it needs to be moved. Please feel free to make a > > > > > >>> patch if you have a better idea, I'll be glad to test it. > > > > > >> > > > > > >> I might have just been distracted by the common "vfp" prefix. It's > > > > > >> possible that the text section shuffling just ended up being very large, > > > > > >> so probably this patch is right then! > > > > > >> > > > > > > > > > > > > I already sent a fix for this issue: > > > > > > > > > > > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > > > > > > > > > > > > > > The offending commit contains stable tag, so I assume that fixes tag is > > > > > mandatory. Yours patch misses the fixes tag. > > > > > > > > Russell, mind adding that? Or would you like me to update the patch in > > > > the patch system? > > > > > > Rather than adding the IT, I'm suggesting that we solve it a different > > > way - ensuring that the two bits of code are co-located. There's no > > > reason for them to be separated, and the assembly code entry point is > > > already called indirectly. > > > > > > The problem is the assembly ends up in the .text section which ends up > > > at the start of the binary, but depending on the compiler, functions > > > in .c files end up in their own sections. It would be good if, as > > > Dmitry has shown that it is indeed possible, to have them co-located. > > > > Why is that better? I provided a minimal fix which has zero impact on > > ARM builds, and minimal impact on Thumb2 builds, given that it retains > > the exact same semantics as before, but using a different opcode. > > I think you just described the reason there. Why should we force > everything to use a different opcode when a short jump _should_ > suffice? > Why should a short jump suffice? The call is to vfp_kmode_exception(), which we only call in exceptional cases. Why would we want to keep that in close proximity? > Your patch may be a single line, but it has a slightly greater > impact than the alternative two line solution. >
22.10.2020 19:23, Russell King - ARM Linux admin пишет: > On Thu, Oct 22, 2020 at 06:20:40PM +0200, Ard Biesheuvel wrote: >> On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin >> <linux@armlinux.org.uk> wrote: >>> >>> On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: >>>> On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: >>>>> >>>>> 22.10.2020 10:06, Ard Biesheuvel пишет: >>>>>> On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: >>>>>>> >>>>>>> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: >>>>>>>> 22.10.2020 02:40, Kees Cook пишет: >>>>>>>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: >>>>>>>>>> The vfp_kmode_exception() function now is unreachable using relative >>>>>>>>>> branching in THUMB2 kernel configuration, resulting in a "relocation >>>>>>>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" >>>>>>>>>> linker error. Let's use long jump in order to fix the issue. >>>>>>>>> >>>>>>>>> Eek. Is this with gcc or clang? >>>>>>>> >>>>>>>> GCC 9.3.0 >>>>>>>> >>>>>>>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") >>>>>>>>> >>>>>>>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? >>>>>>>>> That commit may have implicitly moved the location of .vfp11_veneer, >>>>>>>>> though I thought I had chosen the correct position. >>>>>>>> >>>>>>>> I re-checked that the fixes tag is correct. >>>>>>>> >>>>>>>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> >>>>>>>>>> --- >>>>>>>>>> arch/arm/vfp/vfphw.S | 3 ++- >>>>>>>>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>>>>>>>> >>>>>>>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S >>>>>>>>>> index 4fcff9f59947..6e2b29f0c48d 100644 >>>>>>>>>> --- a/arch/arm/vfp/vfphw.S >>>>>>>>>> +++ b/arch/arm/vfp/vfphw.S >>>>>>>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) >>>>>>>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions >>>>>>>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode >>>>>>>>>> teq r3, #USR_MODE >>>>>>>>>> - bne vfp_kmode_exception @ Returns through lr >>>>>>>>>> + ldr r1, =vfp_kmode_exception >>>>>>>>>> + bxne r1 @ Returns through lr >>>>>>>>>> >>>>>>>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? >>>>>>>>>> DBGSTR1 "fpexc %08x", r1 >>>>>>>>> >>>>>>>>> This seems like a workaround though? I suspect the vfp11_veneer needs >>>>>>>>> moving? >>>>>>>>> >>>>>>>> >>>>>>>> I don't know where it needs to be moved. Please feel free to make a >>>>>>>> patch if you have a better idea, I'll be glad to test it. >>>>>>> >>>>>>> I might have just been distracted by the common "vfp" prefix. It's >>>>>>> possible that the text section shuffling just ended up being very large, >>>>>>> so probably this patch is right then! >>>>>>> >>>>>> >>>>>> I already sent a fix for this issue: >>>>>> >>>>>> https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 >>>>>> >>>>> >>>>> The offending commit contains stable tag, so I assume that fixes tag is >>>>> mandatory. Yours patch misses the fixes tag. >>>> >>>> Russell, mind adding that? Or would you like me to update the patch in >>>> the patch system? >>> >>> Rather than adding the IT, I'm suggesting that we solve it a different >>> way - ensuring that the two bits of code are co-located. There's no >>> reason for them to be separated, and the assembly code entry point is >>> already called indirectly. >>> >>> The problem is the assembly ends up in the .text section which ends up >>> at the start of the binary, but depending on the compiler, functions >>> in .c files end up in their own sections. It would be good if, as >>> Dmitry has shown that it is indeed possible, to have them co-located. >> >> Why is that better? I provided a minimal fix which has zero impact on >> ARM builds, and minimal impact on Thumb2 builds, given that it retains >> the exact same semantics as before, but using a different opcode. > > I think you just described the reason there. Why should we force > everything to use a different opcode when a short jump _should_ > suffice? > > Your patch may be a single line, but it has a slightly greater > impact than the alternative two line solution. > But the two line change isn't portable to stable kernels as-is, isn't it?
On Thu, Oct 22, 2020 at 07:34:38PM +0300, Dmitry Osipenko wrote: > 22.10.2020 19:23, Russell King - ARM Linux admin пишет: > > On Thu, Oct 22, 2020 at 06:20:40PM +0200, Ard Biesheuvel wrote: > >> On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin > >> <linux@armlinux.org.uk> wrote: > >>> > >>> On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > >>>> On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > >>>>> > >>>>> 22.10.2020 10:06, Ard Biesheuvel пишет: > >>>>>> On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > >>>>>>> > >>>>>>> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > >>>>>>>> 22.10.2020 02:40, Kees Cook пишет: > >>>>>>>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > >>>>>>>>>> The vfp_kmode_exception() function now is unreachable using relative > >>>>>>>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > >>>>>>>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > >>>>>>>>>> linker error. Let's use long jump in order to fix the issue. > >>>>>>>>> > >>>>>>>>> Eek. Is this with gcc or clang? > >>>>>>>> > >>>>>>>> GCC 9.3.0 > >>>>>>>> > >>>>>>>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > >>>>>>>>> > >>>>>>>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > >>>>>>>>> That commit may have implicitly moved the location of .vfp11_veneer, > >>>>>>>>> though I thought I had chosen the correct position. > >>>>>>>> > >>>>>>>> I re-checked that the fixes tag is correct. > >>>>>>>> > >>>>>>>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > >>>>>>>>>> --- > >>>>>>>>>> arch/arm/vfp/vfphw.S | 3 ++- > >>>>>>>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > >>>>>>>>>> > >>>>>>>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > >>>>>>>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > >>>>>>>>>> --- a/arch/arm/vfp/vfphw.S > >>>>>>>>>> +++ b/arch/arm/vfp/vfphw.S > >>>>>>>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > >>>>>>>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > >>>>>>>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > >>>>>>>>>> teq r3, #USR_MODE > >>>>>>>>>> - bne vfp_kmode_exception @ Returns through lr > >>>>>>>>>> + ldr r1, =vfp_kmode_exception > >>>>>>>>>> + bxne r1 @ Returns through lr > >>>>>>>>>> > >>>>>>>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > >>>>>>>>>> DBGSTR1 "fpexc %08x", r1 > >>>>>>>>> > >>>>>>>>> This seems like a workaround though? I suspect the vfp11_veneer needs > >>>>>>>>> moving? > >>>>>>>>> > >>>>>>>> > >>>>>>>> I don't know where it needs to be moved. Please feel free to make a > >>>>>>>> patch if you have a better idea, I'll be glad to test it. > >>>>>>> > >>>>>>> I might have just been distracted by the common "vfp" prefix. It's > >>>>>>> possible that the text section shuffling just ended up being very large, > >>>>>>> so probably this patch is right then! > >>>>>>> > >>>>>> > >>>>>> I already sent a fix for this issue: > >>>>>> > >>>>>> https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > >>>>>> > >>>>> > >>>>> The offending commit contains stable tag, so I assume that fixes tag is > >>>>> mandatory. Yours patch misses the fixes tag. > >>>> > >>>> Russell, mind adding that? Or would you like me to update the patch in > >>>> the patch system? > >>> > >>> Rather than adding the IT, I'm suggesting that we solve it a different > >>> way - ensuring that the two bits of code are co-located. There's no > >>> reason for them to be separated, and the assembly code entry point is > >>> already called indirectly. > >>> > >>> The problem is the assembly ends up in the .text section which ends up > >>> at the start of the binary, but depending on the compiler, functions > >>> in .c files end up in their own sections. It would be good if, as > >>> Dmitry has shown that it is indeed possible, to have them co-located. > >> > >> Why is that better? I provided a minimal fix which has zero impact on > >> ARM builds, and minimal impact on Thumb2 builds, given that it retains > >> the exact same semantics as before, but using a different opcode. > > > > I think you just described the reason there. Why should we force > > everything to use a different opcode when a short jump _should_ > > suffice? > > > > Your patch may be a single line, but it has a slightly greater > > impact than the alternative two line solution. > > > > But the two line change isn't portable to stable kernels as-is, isn't it? Why not?
On Thu, 22 Oct 2020 at 19:38, Russell King - ARM Linux admin <linux@armlinux.org.uk> wrote: > > On Thu, Oct 22, 2020 at 07:34:38PM +0300, Dmitry Osipenko wrote: > > 22.10.2020 19:23, Russell King - ARM Linux admin пишет: > > > On Thu, Oct 22, 2020 at 06:20:40PM +0200, Ard Biesheuvel wrote: > > >> On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin > > >> <linux@armlinux.org.uk> wrote: > > >>> > > >>> On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > > >>>> On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > > >>>>> > > >>>>> 22.10.2020 10:06, Ard Biesheuvel пишет: > > >>>>>> On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > > >>>>>>> > > >>>>>>> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > >>>>>>>> 22.10.2020 02:40, Kees Cook пишет: > > >>>>>>>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > >>>>>>>>>> The vfp_kmode_exception() function now is unreachable using relative > > >>>>>>>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > >>>>>>>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > >>>>>>>>>> linker error. Let's use long jump in order to fix the issue. > > >>>>>>>>> > > >>>>>>>>> Eek. Is this with gcc or clang? > > >>>>>>>> > > >>>>>>>> GCC 9.3.0 > > >>>>>>>> > > >>>>>>>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > >>>>>>>>> > > >>>>>>>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > >>>>>>>>> That commit may have implicitly moved the location of .vfp11_veneer, > > >>>>>>>>> though I thought I had chosen the correct position. > > >>>>>>>> > > >>>>>>>> I re-checked that the fixes tag is correct. > > >>>>>>>> > > >>>>>>>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > >>>>>>>>>> --- > > >>>>>>>>>> arch/arm/vfp/vfphw.S | 3 ++- > > >>>>>>>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > >>>>>>>>>> > > >>>>>>>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > >>>>>>>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > >>>>>>>>>> --- a/arch/arm/vfp/vfphw.S > > >>>>>>>>>> +++ b/arch/arm/vfp/vfphw.S > > >>>>>>>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > >>>>>>>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > >>>>>>>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > >>>>>>>>>> teq r3, #USR_MODE > > >>>>>>>>>> - bne vfp_kmode_exception @ Returns through lr > > >>>>>>>>>> + ldr r1, =vfp_kmode_exception > > >>>>>>>>>> + bxne r1 @ Returns through lr > > >>>>>>>>>> > > >>>>>>>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > >>>>>>>>>> DBGSTR1 "fpexc %08x", r1 > > >>>>>>>>> > > >>>>>>>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > >>>>>>>>> moving? > > >>>>>>>>> > > >>>>>>>> > > >>>>>>>> I don't know where it needs to be moved. Please feel free to make a > > >>>>>>>> patch if you have a better idea, I'll be glad to test it. > > >>>>>>> > > >>>>>>> I might have just been distracted by the common "vfp" prefix. It's > > >>>>>>> possible that the text section shuffling just ended up being very large, > > >>>>>>> so probably this patch is right then! > > >>>>>>> > > >>>>>> > > >>>>>> I already sent a fix for this issue: > > >>>>>> > > >>>>>> https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > >>>>>> > > >>>>> > > >>>>> The offending commit contains stable tag, so I assume that fixes tag is > > >>>>> mandatory. Yours patch misses the fixes tag. > > >>>> > > >>>> Russell, mind adding that? Or would you like me to update the patch in > > >>>> the patch system? > > >>> > > >>> Rather than adding the IT, I'm suggesting that we solve it a different > > >>> way - ensuring that the two bits of code are co-located. There's no > > >>> reason for them to be separated, and the assembly code entry point is > > >>> already called indirectly. > > >>> > > >>> The problem is the assembly ends up in the .text section which ends up > > >>> at the start of the binary, but depending on the compiler, functions > > >>> in .c files end up in their own sections. It would be good if, as > > >>> Dmitry has shown that it is indeed possible, to have them co-located. > > >> > > >> Why is that better? I provided a minimal fix which has zero impact on > > >> ARM builds, and minimal impact on Thumb2 builds, given that it retains > > >> the exact same semantics as before, but using a different opcode. > > > > > > I think you just described the reason there. Why should we force > > > everything to use a different opcode when a short jump _should_ > > > suffice? > > > > > > Your patch may be a single line, but it has a slightly greater > > > impact than the alternative two line solution. > > > > > > > But the two line change isn't portable to stable kernels as-is, isn't it? > > Why not? > In any case, I'd prefer not to dump VFP exception handling code into the .vfp11_veneer section, which is documented as below, and typically empty in our case, given that the only FP code we have in the kernel is NEON code. """ The '--vfp11-denorm-fix' switch enables a link-time workaround for a bug in certain VFP11 coprocessor hardware, which sometimes allows instructions with denorm operands (which must be handled by support code) to have those operands overwritten by subsequent instructions before the support code can read the intended values. The bug may be avoided in scalar mode if you allow at least one intervening instruction between a VFP11 instruction which uses a register and another instruction which writes to the same register, or at least two intervening instructions if vector mode is in use. The bug only affects full-compliance floating-point mode: you do not need this workaround if you are using "runfast" mode. Please contact ARM for further details. If you know you are using buggy VFP11 hardware, you can enable this workaround by specifying the linker option '--vfp-denorm-fix=scalar' if you are using the VFP11 scalar mode only, or '--vfp-denorm-fix=vector' if you are using vector mode (the latter also works for scalar code). The default is '--vfp-denorm-fix=none'. If the workaround is enabled, instructions are scanned for potentially-troublesome sequences, and a veneer is created for each such sequence which may trigger the erratum. The veneer consists of the first instruction of the sequence and a branch back to the subsequent instruction. The original instruction is then replaced with a branch to the veneer. The extra cycles required to call and return from the veneer are sufficient to avoid the erratum in both the scalar and vector cases. """
On Thu, Oct 22, 2020 at 06:33:17PM +0200, Ard Biesheuvel wrote: > On Thu, 22 Oct 2020 at 18:23, Russell King - ARM Linux admin > <linux@armlinux.org.uk> wrote: > > > > On Thu, Oct 22, 2020 at 06:20:40PM +0200, Ard Biesheuvel wrote: > > > On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin > > > <linux@armlinux.org.uk> wrote: > > > > > > > > On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > > > > > On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > > > > > > > > > > > > 22.10.2020 10:06, Ard Biesheuvel пишет: > > > > > > > On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > > > > > > >> > > > > > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > > > > > >>> 22.10.2020 02:40, Kees Cook пишет: > > > > > > >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > > > > > >>>>> The vfp_kmode_exception() function now is unreachable using relative > > > > > > >>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > > > > > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > > > > > >>>>> linker error. Let's use long jump in order to fix the issue. > > > > > > >>>> > > > > > > >>>> Eek. Is this with gcc or clang? > > > > > > >>> > > > > > > >>> GCC 9.3.0 > > > > > > >>> > > > > > > >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > > > > > >>>> > > > > > > >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > > > > > >>>> That commit may have implicitly moved the location of .vfp11_veneer, > > > > > > >>>> though I thought I had chosen the correct position. > > > > > > >>> > > > > > > >>> I re-checked that the fixes tag is correct. > > > > > > >>> > > > > > > >>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > > > > > >>>>> --- > > > > > > >>>>> arch/arm/vfp/vfphw.S | 3 ++- > > > > > > >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > >>>>> > > > > > > >>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > > > > > >>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > > > > > >>>>> --- a/arch/arm/vfp/vfphw.S > > > > > > >>>>> +++ b/arch/arm/vfp/vfphw.S > > > > > > >>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > > > > > >>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > > > > > >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > > > > > >>>>> teq r3, #USR_MODE > > > > > > >>>>> - bne vfp_kmode_exception @ Returns through lr > > > > > > >>>>> + ldr r1, =vfp_kmode_exception > > > > > > >>>>> + bxne r1 @ Returns through lr > > > > > > >>>>> > > > > > > >>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > > > > > >>>>> DBGSTR1 "fpexc %08x", r1 > > > > > > >>>> > > > > > > >>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > > > > > >>>> moving? > > > > > > >>>> > > > > > > >>> > > > > > > >>> I don't know where it needs to be moved. Please feel free to make a > > > > > > >>> patch if you have a better idea, I'll be glad to test it. > > > > > > >> > > > > > > >> I might have just been distracted by the common "vfp" prefix. It's > > > > > > >> possible that the text section shuffling just ended up being very large, > > > > > > >> so probably this patch is right then! > > > > > > >> > > > > > > > > > > > > > > I already sent a fix for this issue: > > > > > > > > > > > > > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > > > > > > > > > > > > > > > > > The offending commit contains stable tag, so I assume that fixes tag is > > > > > > mandatory. Yours patch misses the fixes tag. > > > > > > > > > > Russell, mind adding that? Or would you like me to update the patch in > > > > > the patch system? > > > > > > > > Rather than adding the IT, I'm suggesting that we solve it a different > > > > way - ensuring that the two bits of code are co-located. There's no > > > > reason for them to be separated, and the assembly code entry point is > > > > already called indirectly. > > > > > > > > The problem is the assembly ends up in the .text section which ends up > > > > at the start of the binary, but depending on the compiler, functions > > > > in .c files end up in their own sections. It would be good if, as > > > > Dmitry has shown that it is indeed possible, to have them co-located. > > > > > > Why is that better? I provided a minimal fix which has zero impact on > > > ARM builds, and minimal impact on Thumb2 builds, given that it retains > > > the exact same semantics as before, but using a different opcode. > > > > I think you just described the reason there. Why should we force > > everything to use a different opcode when a short jump _should_ > > suffice? > > > > Why should a short jump suffice? The call is to vfp_kmode_exception(), > which we only call in exceptional cases. Why would we want to keep > that in close proximity? You're thinking about it in terms of what happens when the branch is taken, rather than also considering that this code path is also traversed for _every_ single time that we enter the support code not just for kernel mode.
On Thu, Oct 22, 2020 at 07:47:57PM +0200, Ard Biesheuvel wrote: > On Thu, 22 Oct 2020 at 19:38, Russell King - ARM Linux admin > <linux@armlinux.org.uk> wrote: > > > > On Thu, Oct 22, 2020 at 07:34:38PM +0300, Dmitry Osipenko wrote: > > > 22.10.2020 19:23, Russell King - ARM Linux admin пишет: > > > > On Thu, Oct 22, 2020 at 06:20:40PM +0200, Ard Biesheuvel wrote: > > > >> On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin > > > >> <linux@armlinux.org.uk> wrote: > > > >>> > > > >>> On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > > > >>>> On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > > > >>>>> > > > >>>>> 22.10.2020 10:06, Ard Biesheuvel пишет: > > > >>>>>> On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > > > >>>>>>> > > > >>>>>>> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > > >>>>>>>> 22.10.2020 02:40, Kees Cook пишет: > > > >>>>>>>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > > >>>>>>>>>> The vfp_kmode_exception() function now is unreachable using relative > > > >>>>>>>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > > >>>>>>>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > > >>>>>>>>>> linker error. Let's use long jump in order to fix the issue. > > > >>>>>>>>> > > > >>>>>>>>> Eek. Is this with gcc or clang? > > > >>>>>>>> > > > >>>>>>>> GCC 9.3.0 > > > >>>>>>>> > > > >>>>>>>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > > >>>>>>>>> > > > >>>>>>>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > > >>>>>>>>> That commit may have implicitly moved the location of .vfp11_veneer, > > > >>>>>>>>> though I thought I had chosen the correct position. > > > >>>>>>>> > > > >>>>>>>> I re-checked that the fixes tag is correct. > > > >>>>>>>> > > > >>>>>>>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > > >>>>>>>>>> --- > > > >>>>>>>>>> arch/arm/vfp/vfphw.S | 3 ++- > > > >>>>>>>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > > >>>>>>>>>> > > > >>>>>>>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > > >>>>>>>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > > >>>>>>>>>> --- a/arch/arm/vfp/vfphw.S > > > >>>>>>>>>> +++ b/arch/arm/vfp/vfphw.S > > > >>>>>>>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > > >>>>>>>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > > >>>>>>>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > > >>>>>>>>>> teq r3, #USR_MODE > > > >>>>>>>>>> - bne vfp_kmode_exception @ Returns through lr > > > >>>>>>>>>> + ldr r1, =vfp_kmode_exception > > > >>>>>>>>>> + bxne r1 @ Returns through lr > > > >>>>>>>>>> > > > >>>>>>>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > > >>>>>>>>>> DBGSTR1 "fpexc %08x", r1 > > > >>>>>>>>> > > > >>>>>>>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > > >>>>>>>>> moving? > > > >>>>>>>>> > > > >>>>>>>> > > > >>>>>>>> I don't know where it needs to be moved. Please feel free to make a > > > >>>>>>>> patch if you have a better idea, I'll be glad to test it. > > > >>>>>>> > > > >>>>>>> I might have just been distracted by the common "vfp" prefix. It's > > > >>>>>>> possible that the text section shuffling just ended up being very large, > > > >>>>>>> so probably this patch is right then! > > > >>>>>>> > > > >>>>>> > > > >>>>>> I already sent a fix for this issue: > > > >>>>>> > > > >>>>>> https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > >>>>>> > > > >>>>> > > > >>>>> The offending commit contains stable tag, so I assume that fixes tag is > > > >>>>> mandatory. Yours patch misses the fixes tag. > > > >>>> > > > >>>> Russell, mind adding that? Or would you like me to update the patch in > > > >>>> the patch system? > > > >>> > > > >>> Rather than adding the IT, I'm suggesting that we solve it a different > > > >>> way - ensuring that the two bits of code are co-located. There's no > > > >>> reason for them to be separated, and the assembly code entry point is > > > >>> already called indirectly. > > > >>> > > > >>> The problem is the assembly ends up in the .text section which ends up > > > >>> at the start of the binary, but depending on the compiler, functions > > > >>> in .c files end up in their own sections. It would be good if, as > > > >>> Dmitry has shown that it is indeed possible, to have them co-located. > > > >> > > > >> Why is that better? I provided a minimal fix which has zero impact on > > > >> ARM builds, and minimal impact on Thumb2 builds, given that it retains > > > >> the exact same semantics as before, but using a different opcode. > > > > > > > > I think you just described the reason there. Why should we force > > > > everything to use a different opcode when a short jump _should_ > > > > suffice? > > > > > > > > Your patch may be a single line, but it has a slightly greater > > > > impact than the alternative two line solution. > > > > > > > > > > But the two line change isn't portable to stable kernels as-is, isn't it? > > > > Why not? > > > > In any case, I'd prefer not to dump VFP exception handling code into > the .vfp11_veneer section, which is documented as below, and typically > empty in our case, given that the only FP code we have in the kernel > is NEON code. This is getting out of hand, and really getting beyond a joke. I didn't say put it in the ".vfp11_veneer" section.
On Thu, 22 Oct 2020 at 19:50, Russell King - ARM Linux admin <linux@armlinux.org.uk> wrote: > > On Thu, Oct 22, 2020 at 07:47:57PM +0200, Ard Biesheuvel wrote: > > On Thu, 22 Oct 2020 at 19:38, Russell King - ARM Linux admin > > <linux@armlinux.org.uk> wrote: > > > > > > On Thu, Oct 22, 2020 at 07:34:38PM +0300, Dmitry Osipenko wrote: > > > > 22.10.2020 19:23, Russell King - ARM Linux admin пишет: > > > > > On Thu, Oct 22, 2020 at 06:20:40PM +0200, Ard Biesheuvel wrote: > > > > >> On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin > > > > >> <linux@armlinux.org.uk> wrote: > > > > >>> > > > > >>> On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > > > > >>>> On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > > > > >>>>> > > > > >>>>> 22.10.2020 10:06, Ard Biesheuvel пишет: > > > > >>>>>> On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > > > > >>>>>>> > > > > >>>>>>> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > > > >>>>>>>> 22.10.2020 02:40, Kees Cook пишет: > > > > >>>>>>>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > > > >>>>>>>>>> The vfp_kmode_exception() function now is unreachable using relative > > > > >>>>>>>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > > > >>>>>>>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > > > >>>>>>>>>> linker error. Let's use long jump in order to fix the issue. > > > > >>>>>>>>> > > > > >>>>>>>>> Eek. Is this with gcc or clang? > > > > >>>>>>>> > > > > >>>>>>>> GCC 9.3.0 > > > > >>>>>>>> > > > > >>>>>>>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > > > >>>>>>>>> > > > > >>>>>>>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > > > >>>>>>>>> That commit may have implicitly moved the location of .vfp11_veneer, > > > > >>>>>>>>> though I thought I had chosen the correct position. > > > > >>>>>>>> > > > > >>>>>>>> I re-checked that the fixes tag is correct. > > > > >>>>>>>> > > > > >>>>>>>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > > > >>>>>>>>>> --- > > > > >>>>>>>>>> arch/arm/vfp/vfphw.S | 3 ++- > > > > >>>>>>>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > > > >>>>>>>>>> > > > > >>>>>>>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > > > >>>>>>>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > > > >>>>>>>>>> --- a/arch/arm/vfp/vfphw.S > > > > >>>>>>>>>> +++ b/arch/arm/vfp/vfphw.S > > > > >>>>>>>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > > > >>>>>>>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > > > >>>>>>>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > > > >>>>>>>>>> teq r3, #USR_MODE > > > > >>>>>>>>>> - bne vfp_kmode_exception @ Returns through lr > > > > >>>>>>>>>> + ldr r1, =vfp_kmode_exception > > > > >>>>>>>>>> + bxne r1 @ Returns through lr > > > > >>>>>>>>>> > > > > >>>>>>>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > > > >>>>>>>>>> DBGSTR1 "fpexc %08x", r1 > > > > >>>>>>>>> > > > > >>>>>>>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > > > >>>>>>>>> moving? > > > > >>>>>>>>> > > > > >>>>>>>> > > > > >>>>>>>> I don't know where it needs to be moved. Please feel free to make a > > > > >>>>>>>> patch if you have a better idea, I'll be glad to test it. > > > > >>>>>>> > > > > >>>>>>> I might have just been distracted by the common "vfp" prefix. It's > > > > >>>>>>> possible that the text section shuffling just ended up being very large, > > > > >>>>>>> so probably this patch is right then! > > > > >>>>>>> > > > > >>>>>> > > > > >>>>>> I already sent a fix for this issue: > > > > >>>>>> > > > > >>>>>> https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > > >>>>>> > > > > >>>>> > > > > >>>>> The offending commit contains stable tag, so I assume that fixes tag is > > > > >>>>> mandatory. Yours patch misses the fixes tag. > > > > >>>> > > > > >>>> Russell, mind adding that? Or would you like me to update the patch in > > > > >>>> the patch system? > > > > >>> > > > > >>> Rather than adding the IT, I'm suggesting that we solve it a different > > > > >>> way - ensuring that the two bits of code are co-located. There's no > > > > >>> reason for them to be separated, and the assembly code entry point is > > > > >>> already called indirectly. > > > > >>> > > > > >>> The problem is the assembly ends up in the .text section which ends up > > > > >>> at the start of the binary, but depending on the compiler, functions > > > > >>> in .c files end up in their own sections. It would be good if, as > > > > >>> Dmitry has shown that it is indeed possible, to have them co-located. > > > > >> > > > > >> Why is that better? I provided a minimal fix which has zero impact on > > > > >> ARM builds, and minimal impact on Thumb2 builds, given that it retains > > > > >> the exact same semantics as before, but using a different opcode. > > > > > > > > > > I think you just described the reason there. Why should we force > > > > > everything to use a different opcode when a short jump _should_ > > > > > suffice? > > > > > > > > > > Your patch may be a single line, but it has a slightly greater > > > > > impact than the alternative two line solution. > > > > > > > > > > > > > But the two line change isn't portable to stable kernels as-is, isn't it? > > > > > > Why not? > > > > > > > In any case, I'd prefer not to dump VFP exception handling code into > > the .vfp11_veneer section, which is documented as below, and typically > > empty in our case, given that the only FP code we have in the kernel > > is NEON code. > > This is getting out of hand, and really getting beyond a joke. I > didn't say put it in the ".vfp11_veneer" section. > No, but that is what Dmitry's patch proposes.
On Thu, 22 Oct 2020 at 19:48, Russell King - ARM Linux admin <linux@armlinux.org.uk> wrote: > > On Thu, Oct 22, 2020 at 06:33:17PM +0200, Ard Biesheuvel wrote: > > On Thu, 22 Oct 2020 at 18:23, Russell King - ARM Linux admin > > <linux@armlinux.org.uk> wrote: > > > > > > On Thu, Oct 22, 2020 at 06:20:40PM +0200, Ard Biesheuvel wrote: > > > > On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin > > > > <linux@armlinux.org.uk> wrote: > > > > > > > > > > On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > > > > > > On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > > > > > > > > > > > > > > 22.10.2020 10:06, Ard Biesheuvel пишет: > > > > > > > > On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > > > > > > > >> > > > > > > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > > > > > > >>> 22.10.2020 02:40, Kees Cook пишет: > > > > > > > >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > > > > > > >>>>> The vfp_kmode_exception() function now is unreachable using relative > > > > > > > >>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > > > > > > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > > > > > > >>>>> linker error. Let's use long jump in order to fix the issue. > > > > > > > >>>> > > > > > > > >>>> Eek. Is this with gcc or clang? > > > > > > > >>> > > > > > > > >>> GCC 9.3.0 > > > > > > > >>> > > > > > > > >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > > > > > > >>>> > > > > > > > >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > > > > > > >>>> That commit may have implicitly moved the location of .vfp11_veneer, > > > > > > > >>>> though I thought I had chosen the correct position. > > > > > > > >>> > > > > > > > >>> I re-checked that the fixes tag is correct. > > > > > > > >>> > > > > > > > >>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > > > > > > >>>>> --- > > > > > > > >>>>> arch/arm/vfp/vfphw.S | 3 ++- > > > > > > > >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > >>>>> > > > > > > > >>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > > > > > > >>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > > > > > > >>>>> --- a/arch/arm/vfp/vfphw.S > > > > > > > >>>>> +++ b/arch/arm/vfp/vfphw.S > > > > > > > >>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > > > > > > >>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > > > > > > >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > > > > > > >>>>> teq r3, #USR_MODE > > > > > > > >>>>> - bne vfp_kmode_exception @ Returns through lr > > > > > > > >>>>> + ldr r1, =vfp_kmode_exception > > > > > > > >>>>> + bxne r1 @ Returns through lr > > > > > > > >>>>> > > > > > > > >>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > > > > > > >>>>> DBGSTR1 "fpexc %08x", r1 > > > > > > > >>>> > > > > > > > >>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > > > > > > >>>> moving? > > > > > > > >>>> > > > > > > > >>> > > > > > > > >>> I don't know where it needs to be moved. Please feel free to make a > > > > > > > >>> patch if you have a better idea, I'll be glad to test it. > > > > > > > >> > > > > > > > >> I might have just been distracted by the common "vfp" prefix. It's > > > > > > > >> possible that the text section shuffling just ended up being very large, > > > > > > > >> so probably this patch is right then! > > > > > > > >> > > > > > > > > > > > > > > > > I already sent a fix for this issue: > > > > > > > > > > > > > > > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > > > > > > > > > > > > > > > > > > > > The offending commit contains stable tag, so I assume that fixes tag is > > > > > > > mandatory. Yours patch misses the fixes tag. > > > > > > > > > > > > Russell, mind adding that? Or would you like me to update the patch in > > > > > > the patch system? > > > > > > > > > > Rather than adding the IT, I'm suggesting that we solve it a different > > > > > way - ensuring that the two bits of code are co-located. There's no > > > > > reason for them to be separated, and the assembly code entry point is > > > > > already called indirectly. > > > > > > > > > > The problem is the assembly ends up in the .text section which ends up > > > > > at the start of the binary, but depending on the compiler, functions > > > > > in .c files end up in their own sections. It would be good if, as > > > > > Dmitry has shown that it is indeed possible, to have them co-located. > > > > > > > > Why is that better? I provided a minimal fix which has zero impact on > > > > ARM builds, and minimal impact on Thumb2 builds, given that it retains > > > > the exact same semantics as before, but using a different opcode. > > > > > > I think you just described the reason there. Why should we force > > > everything to use a different opcode when a short jump _should_ > > > suffice? > > > > > > > Why should a short jump suffice? The call is to vfp_kmode_exception(), > > which we only call in exceptional cases. Why would we want to keep > > that in close proximity? > > You're thinking about it in terms of what happens when the branch is > taken, rather than also considering that this code path is also > traversed for _every_ single time that we enter the support code > not just for kernel mode. > True. If 2 bytes of additional opcode are the concern here, we can change the current sequence 6: f093 0f10 teq r3, #16 a: f47f affe bne.w 0 <vfp_kmode_exception> to 6: 2b10 cmp r3, #16 8: bf18 it ne a: f7ff bffe bne.w 0 <vfp_kmode_exception> which takes up the exact same space.
22.10.2020 20:38, Russell King - ARM Linux admin пишет: ... >> But the two line change isn't portable to stable kernels as-is, isn't it? > > Why not? > I assume we will need to define a new section, no?
On Thu, 22 Oct 2020 at 19:59, Ard Biesheuvel <ardb@kernel.org> wrote: > > On Thu, 22 Oct 2020 at 19:48, Russell King - ARM Linux admin > <linux@armlinux.org.uk> wrote: > > > > On Thu, Oct 22, 2020 at 06:33:17PM +0200, Ard Biesheuvel wrote: > > > On Thu, 22 Oct 2020 at 18:23, Russell King - ARM Linux admin > > > <linux@armlinux.org.uk> wrote: > > > > > > > > On Thu, Oct 22, 2020 at 06:20:40PM +0200, Ard Biesheuvel wrote: > > > > > On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin > > > > > <linux@armlinux.org.uk> wrote: > > > > > > > > > > > > On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > > > > > > > On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > > > > > > > > > > > > > > > > 22.10.2020 10:06, Ard Biesheuvel пишет: > > > > > > > > > On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > > > > > > > > >> > > > > > > > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > > > > > > > >>> 22.10.2020 02:40, Kees Cook пишет: > > > > > > > > >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > > > > > > > >>>>> The vfp_kmode_exception() function now is unreachable using relative > > > > > > > > >>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > > > > > > > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > > > > > > > >>>>> linker error. Let's use long jump in order to fix the issue. > > > > > > > > >>>> > > > > > > > > >>>> Eek. Is this with gcc or clang? > > > > > > > > >>> > > > > > > > > >>> GCC 9.3.0 > > > > > > > > >>> > > > > > > > > >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > > > > > > > >>>> > > > > > > > > >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > > > > > > > >>>> That commit may have implicitly moved the location of .vfp11_veneer, > > > > > > > > >>>> though I thought I had chosen the correct position. > > > > > > > > >>> > > > > > > > > >>> I re-checked that the fixes tag is correct. > > > > > > > > >>> > > > > > > > > >>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > > > > > > > >>>>> --- > > > > > > > > >>>>> arch/arm/vfp/vfphw.S | 3 ++- > > > > > > > > >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > >>>>> > > > > > > > > >>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > > > > > > > >>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > > > > > > > >>>>> --- a/arch/arm/vfp/vfphw.S > > > > > > > > >>>>> +++ b/arch/arm/vfp/vfphw.S > > > > > > > > >>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > > > > > > > >>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > > > > > > > >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > > > > > > > >>>>> teq r3, #USR_MODE > > > > > > > > >>>>> - bne vfp_kmode_exception @ Returns through lr > > > > > > > > >>>>> + ldr r1, =vfp_kmode_exception > > > > > > > > >>>>> + bxne r1 @ Returns through lr > > > > > > > > >>>>> > > > > > > > > >>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > > > > > > > >>>>> DBGSTR1 "fpexc %08x", r1 > > > > > > > > >>>> > > > > > > > > >>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > > > > > > > >>>> moving? > > > > > > > > >>>> > > > > > > > > >>> > > > > > > > > >>> I don't know where it needs to be moved. Please feel free to make a > > > > > > > > >>> patch if you have a better idea, I'll be glad to test it. > > > > > > > > >> > > > > > > > > >> I might have just been distracted by the common "vfp" prefix. It's > > > > > > > > >> possible that the text section shuffling just ended up being very large, > > > > > > > > >> so probably this patch is right then! > > > > > > > > >> > > > > > > > > > > > > > > > > > > I already sent a fix for this issue: > > > > > > > > > > > > > > > > > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > > > > > > > > > > > > > > > > > > > > > > > The offending commit contains stable tag, so I assume that fixes tag is > > > > > > > > mandatory. Yours patch misses the fixes tag. > > > > > > > > > > > > > > Russell, mind adding that? Or would you like me to update the patch in > > > > > > > the patch system? > > > > > > > > > > > > Rather than adding the IT, I'm suggesting that we solve it a different > > > > > > way - ensuring that the two bits of code are co-located. There's no > > > > > > reason for them to be separated, and the assembly code entry point is > > > > > > already called indirectly. > > > > > > > > > > > > The problem is the assembly ends up in the .text section which ends up > > > > > > at the start of the binary, but depending on the compiler, functions > > > > > > in .c files end up in their own sections. It would be good if, as > > > > > > Dmitry has shown that it is indeed possible, to have them co-located. > > > > > > > > > > Why is that better? I provided a minimal fix which has zero impact on > > > > > ARM builds, and minimal impact on Thumb2 builds, given that it retains > > > > > the exact same semantics as before, but using a different opcode. > > > > > > > > I think you just described the reason there. Why should we force > > > > everything to use a different opcode when a short jump _should_ > > > > suffice? > > > > > > > > > > Why should a short jump suffice? The call is to vfp_kmode_exception(), > > > which we only call in exceptional cases. Why would we want to keep > > > that in close proximity? > > > > You're thinking about it in terms of what happens when the branch is > > taken, rather than also considering that this code path is also > > traversed for _every_ single time that we enter the support code > > not just for kernel mode. > > > > True. If 2 bytes of additional opcode are the concern here, we can > change the current sequence > > 6: f093 0f10 teq r3, #16 > a: f47f affe bne.w 0 <vfp_kmode_exception> > > to > > 6: 2b10 cmp r3, #16 > 8: bf18 it ne > a: f7ff bffe bne.w 0 <vfp_kmode_exception> > > which takes up the exact same space. BTW this code path looks slightly broken for Thumb-2 in any case: if a FP exception is taken in kernel mode on a Thumb2 kernel, we enter the emulation sequence via call_fpe, which will use the wrong set of value/mask pairs to match the opcode. The minimal fix is to move the call_fpe label to the right place, but I think it might be better to move the check for a FP exception in kernel mode to the handling of __und_svc.
On Mon, 26 Oct 2020 at 09:58, Ard Biesheuvel <ardb@kernel.org> wrote: > > On Thu, 22 Oct 2020 at 19:59, Ard Biesheuvel <ardb@kernel.org> wrote: > > > > On Thu, 22 Oct 2020 at 19:48, Russell King - ARM Linux admin > > <linux@armlinux.org.uk> wrote: > > > > > > On Thu, Oct 22, 2020 at 06:33:17PM +0200, Ard Biesheuvel wrote: > > > > On Thu, 22 Oct 2020 at 18:23, Russell King - ARM Linux admin > > > > <linux@armlinux.org.uk> wrote: > > > > > > > > > > On Thu, Oct 22, 2020 at 06:20:40PM +0200, Ard Biesheuvel wrote: > > > > > > On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin > > > > > > <linux@armlinux.org.uk> wrote: > > > > > > > > > > > > > > On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > > > > > > > > On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > > > > > > > > > > > > > > > > > > 22.10.2020 10:06, Ard Biesheuvel пишет: > > > > > > > > > > On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > > > > > > > > > >> > > > > > > > > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > > > > > > > > >>> 22.10.2020 02:40, Kees Cook пишет: > > > > > > > > > >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > > > > > > > > >>>>> The vfp_kmode_exception() function now is unreachable using relative > > > > > > > > > >>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > > > > > > > > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > > > > > > > > >>>>> linker error. Let's use long jump in order to fix the issue. > > > > > > > > > >>>> > > > > > > > > > >>>> Eek. Is this with gcc or clang? > > > > > > > > > >>> > > > > > > > > > >>> GCC 9.3.0 > > > > > > > > > >>> > > > > > > > > > >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > > > > > > > > >>>> > > > > > > > > > >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > > > > > > > > >>>> That commit may have implicitly moved the location of .vfp11_veneer, > > > > > > > > > >>>> though I thought I had chosen the correct position. > > > > > > > > > >>> > > > > > > > > > >>> I re-checked that the fixes tag is correct. > > > > > > > > > >>> > > > > > > > > > >>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > > > > > > > > >>>>> --- > > > > > > > > > >>>>> arch/arm/vfp/vfphw.S | 3 ++- > > > > > > > > > >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > >>>>> > > > > > > > > > >>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > > > > > > > > >>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > > > > > > > > >>>>> --- a/arch/arm/vfp/vfphw.S > > > > > > > > > >>>>> +++ b/arch/arm/vfp/vfphw.S > > > > > > > > > >>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > > > > > > > > >>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > > > > > > > > >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > > > > > > > > >>>>> teq r3, #USR_MODE > > > > > > > > > >>>>> - bne vfp_kmode_exception @ Returns through lr > > > > > > > > > >>>>> + ldr r1, =vfp_kmode_exception > > > > > > > > > >>>>> + bxne r1 @ Returns through lr > > > > > > > > > >>>>> > > > > > > > > > >>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > > > > > > > > >>>>> DBGSTR1 "fpexc %08x", r1 > > > > > > > > > >>>> > > > > > > > > > >>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > > > > > > > > >>>> moving? > > > > > > > > > >>>> > > > > > > > > > >>> > > > > > > > > > >>> I don't know where it needs to be moved. Please feel free to make a > > > > > > > > > >>> patch if you have a better idea, I'll be glad to test it. > > > > > > > > > >> > > > > > > > > > >> I might have just been distracted by the common "vfp" prefix. It's > > > > > > > > > >> possible that the text section shuffling just ended up being very large, > > > > > > > > > >> so probably this patch is right then! > > > > > > > > > >> > > > > > > > > > > > > > > > > > > > > I already sent a fix for this issue: > > > > > > > > > > > > > > > > > > > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > > > > > > > > > > > > > > > > > > > > > > > > > > The offending commit contains stable tag, so I assume that fixes tag is > > > > > > > > > mandatory. Yours patch misses the fixes tag. > > > > > > > > > > > > > > > > Russell, mind adding that? Or would you like me to update the patch in > > > > > > > > the patch system? > > > > > > > > > > > > > > Rather than adding the IT, I'm suggesting that we solve it a different > > > > > > > way - ensuring that the two bits of code are co-located. There's no > > > > > > > reason for them to be separated, and the assembly code entry point is > > > > > > > already called indirectly. > > > > > > > > > > > > > > The problem is the assembly ends up in the .text section which ends up > > > > > > > at the start of the binary, but depending on the compiler, functions > > > > > > > in .c files end up in their own sections. It would be good if, as > > > > > > > Dmitry has shown that it is indeed possible, to have them co-located. > > > > > > > > > > > > Why is that better? I provided a minimal fix which has zero impact on > > > > > > ARM builds, and minimal impact on Thumb2 builds, given that it retains > > > > > > the exact same semantics as before, but using a different opcode. > > > > > > > > > > I think you just described the reason there. Why should we force > > > > > everything to use a different opcode when a short jump _should_ > > > > > suffice? > > > > > > > > > > > > > Why should a short jump suffice? The call is to vfp_kmode_exception(), > > > > which we only call in exceptional cases. Why would we want to keep > > > > that in close proximity? > > > > > > You're thinking about it in terms of what happens when the branch is > > > taken, rather than also considering that this code path is also > > > traversed for _every_ single time that we enter the support code > > > not just for kernel mode. > > > > > > > True. If 2 bytes of additional opcode are the concern here, we can > > change the current sequence > > > > 6: f093 0f10 teq r3, #16 > > a: f47f affe bne.w 0 <vfp_kmode_exception> > > > > to > > > > 6: 2b10 cmp r3, #16 > > 8: bf18 it ne > > a: f7ff bffe bne.w 0 <vfp_kmode_exception> > > > > which takes up the exact same space. > > BTW this code path looks slightly broken for Thumb-2 in any case: if a > FP exception is taken in kernel mode on a Thumb2 kernel, we enter the > emulation sequence via call_fpe, which will use the wrong set of > value/mask pairs to match the opcode. The minimal fix is to move the > call_fpe label to the right place, but I think it might be better to > move the check for a FP exception in kernel mode to the handling of > __und_svc. Do we have a resolution here? This is causing breakage in kernelci https://kernelci.org/build/id/5f9a834c5ed3c05dd538101b/
On Thu, 29 Oct 2020 at 10:56, Ard Biesheuvel <ardb@kernel.org> wrote: > > On Mon, 26 Oct 2020 at 09:58, Ard Biesheuvel <ardb@kernel.org> wrote: > > > > On Thu, 22 Oct 2020 at 19:59, Ard Biesheuvel <ardb@kernel.org> wrote: > > > > > > On Thu, 22 Oct 2020 at 19:48, Russell King - ARM Linux admin > > > <linux@armlinux.org.uk> wrote: > > > > > > > > On Thu, Oct 22, 2020 at 06:33:17PM +0200, Ard Biesheuvel wrote: > > > > > On Thu, 22 Oct 2020 at 18:23, Russell King - ARM Linux admin > > > > > <linux@armlinux.org.uk> wrote: > > > > > > > > > > > > On Thu, Oct 22, 2020 at 06:20:40PM +0200, Ard Biesheuvel wrote: > > > > > > > On Thu, 22 Oct 2020 at 18:11, Russell King - ARM Linux admin > > > > > > > <linux@armlinux.org.uk> wrote: > > > > > > > > > > > > > > > > On Thu, Oct 22, 2020 at 06:06:32PM +0200, Ard Biesheuvel wrote: > > > > > > > > > On Thu, 22 Oct 2020 at 17:57, Dmitry Osipenko <digetx@gmail.com> wrote: > > > > > > > > > > > > > > > > > > > > 22.10.2020 10:06, Ard Biesheuvel пишет: > > > > > > > > > > > On Thu, 22 Oct 2020 at 05:30, Kees Cook <keescook@chromium.org> wrote: > > > > > > > > > > >> > > > > > > > > > > >> On Thu, Oct 22, 2020 at 03:00:06AM +0300, Dmitry Osipenko wrote: > > > > > > > > > > >>> 22.10.2020 02:40, Kees Cook пишет: > > > > > > > > > > >>>> On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote: > > > > > > > > > > >>>>> The vfp_kmode_exception() function now is unreachable using relative > > > > > > > > > > >>>>> branching in THUMB2 kernel configuration, resulting in a "relocation > > > > > > > > > > >>>>> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" > > > > > > > > > > >>>>> linker error. Let's use long jump in order to fix the issue. > > > > > > > > > > >>>> > > > > > > > > > > >>>> Eek. Is this with gcc or clang? > > > > > > > > > > >>> > > > > > > > > > > >>> GCC 9.3.0 > > > > > > > > > > >>> > > > > > > > > > > >>>>> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") > > > > > > > > > > >>>> > > > > > > > > > > >>>> Are you sure it wasn't 512dd2eebe55 ("arm/build: Add missing sections") ? > > > > > > > > > > >>>> That commit may have implicitly moved the location of .vfp11_veneer, > > > > > > > > > > >>>> though I thought I had chosen the correct position. > > > > > > > > > > >>> > > > > > > > > > > >>> I re-checked that the fixes tag is correct. > > > > > > > > > > >>> > > > > > > > > > > >>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> > > > > > > > > > > >>>>> --- > > > > > > > > > > >>>>> arch/arm/vfp/vfphw.S | 3 ++- > > > > > > > > > > >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > >>>>> > > > > > > > > > > >>>>> diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S > > > > > > > > > > >>>>> index 4fcff9f59947..6e2b29f0c48d 100644 > > > > > > > > > > >>>>> --- a/arch/arm/vfp/vfphw.S > > > > > > > > > > >>>>> +++ b/arch/arm/vfp/vfphw.S > > > > > > > > > > >>>>> @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) > > > > > > > > > > >>>>> ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions > > > > > > > > > > >>>>> and r3, r3, #MODE_MASK @ are supported in kernel mode > > > > > > > > > > >>>>> teq r3, #USR_MODE > > > > > > > > > > >>>>> - bne vfp_kmode_exception @ Returns through lr > > > > > > > > > > >>>>> + ldr r1, =vfp_kmode_exception > > > > > > > > > > >>>>> + bxne r1 @ Returns through lr > > > > > > > > > > >>>>> > > > > > > > > > > >>>>> VFPFMRX r1, FPEXC @ Is the VFP enabled? > > > > > > > > > > >>>>> DBGSTR1 "fpexc %08x", r1 > > > > > > > > > > >>>> > > > > > > > > > > >>>> This seems like a workaround though? I suspect the vfp11_veneer needs > > > > > > > > > > >>>> moving? > > > > > > > > > > >>>> > > > > > > > > > > >>> > > > > > > > > > > >>> I don't know where it needs to be moved. Please feel free to make a > > > > > > > > > > >>> patch if you have a better idea, I'll be glad to test it. > > > > > > > > > > >> > > > > > > > > > > >> I might have just been distracted by the common "vfp" prefix. It's > > > > > > > > > > >> possible that the text section shuffling just ended up being very large, > > > > > > > > > > >> so probably this patch is right then! > > > > > > > > > > >> > > > > > > > > > > > > > > > > > > > > > > I already sent a fix for this issue: > > > > > > > > > > > > > > > > > > > > > > https://www.armlinux.org.uk/developer/patches/viewpatch.php?id=9018/1 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The offending commit contains stable tag, so I assume that fixes tag is > > > > > > > > > > mandatory. Yours patch misses the fixes tag. > > > > > > > > > > > > > > > > > > Russell, mind adding that? Or would you like me to update the patch in > > > > > > > > > the patch system? > > > > > > > > > > > > > > > > Rather than adding the IT, I'm suggesting that we solve it a different > > > > > > > > way - ensuring that the two bits of code are co-located. There's no > > > > > > > > reason for them to be separated, and the assembly code entry point is > > > > > > > > already called indirectly. > > > > > > > > > > > > > > > > The problem is the assembly ends up in the .text section which ends up > > > > > > > > at the start of the binary, but depending on the compiler, functions > > > > > > > > in .c files end up in their own sections. It would be good if, as > > > > > > > > Dmitry has shown that it is indeed possible, to have them co-located. > > > > > > > > > > > > > > Why is that better? I provided a minimal fix which has zero impact on > > > > > > > ARM builds, and minimal impact on Thumb2 builds, given that it retains > > > > > > > the exact same semantics as before, but using a different opcode. > > > > > > > > > > > > I think you just described the reason there. Why should we force > > > > > > everything to use a different opcode when a short jump _should_ > > > > > > suffice? > > > > > > > > > > > > > > > > Why should a short jump suffice? The call is to vfp_kmode_exception(), > > > > > which we only call in exceptional cases. Why would we want to keep > > > > > that in close proximity? > > > > > > > > You're thinking about it in terms of what happens when the branch is > > > > taken, rather than also considering that this code path is also > > > > traversed for _every_ single time that we enter the support code > > > > not just for kernel mode. > > > > > > > > > > True. If 2 bytes of additional opcode are the concern here, we can > > > change the current sequence > > > > > > 6: f093 0f10 teq r3, #16 > > > a: f47f affe bne.w 0 <vfp_kmode_exception> > > > > > > to > > > > > > 6: 2b10 cmp r3, #16 > > > 8: bf18 it ne > > > a: f7ff bffe bne.w 0 <vfp_kmode_exception> > > > > > > which takes up the exact same space. > > > > BTW this code path looks slightly broken for Thumb-2 in any case: if a > > FP exception is taken in kernel mode on a Thumb2 kernel, we enter the > > emulation sequence via call_fpe, which will use the wrong set of > > value/mask pairs to match the opcode. The minimal fix is to move the > > call_fpe label to the right place, but I think it might be better to > > move the check for a FP exception in kernel mode to the handling of > > __und_svc. > > Do we have a resolution here? This is causing breakage in kernelci > > https://kernelci.org/build/id/5f9a834c5ed3c05dd538101b/ Still broken today https://kernelci.org/build/id/5fa0c1a74bdb1ea4063fe7e4/ So the options are a) merge my patch that adds 2 bytes of opcode to the Thumb2 build b) merge Dmitry's patch that adds an unconditional literal load to all builds c) remove kernel mode handling from vfp_support_entry() [my other patch] d) move sections around so that vfp_kmode_exception is guaranteed to be in range. e) do nothing Given the lack of reports about this issue, it is pretty clear that few people use the Thumb2 build (which I find odd, tbh, since it really is much smaller). However, that means that a) is a reasonable fix, since nobody will notice the potential performance hit either, and it can easily be backported to wherever the breakage was introduced. (Note that eff8728fe698, which created the problem is marked cc:stable itself). Going forward, I can refine d) so that we can get rid of the kernel mode path entirely.
03.11.2020 10:24, Ard Biesheuvel пишет: > Still broken today > > https://kernelci.org/build/id/5fa0c1a74bdb1ea4063fe7e4/ > > So the options are > > a) merge my patch that adds 2 bytes of opcode to the Thumb2 build > b) merge Dmitry's patch that adds an unconditional literal load to all builds > c) remove kernel mode handling from vfp_support_entry() [my other patch] > d) move sections around so that vfp_kmode_exception is guaranteed to > be in range. > e) do nothing > > Given the lack of reports about this issue, it is pretty clear that > few people use the Thumb2 build (which I find odd, tbh, since it > really is much smaller). I waited for about a month, hoping that somebody will fix this problem before bothering with bisection, which took quite some time and effort because intermediate commits were broken, and then with creating and sending a patch :) Thumb2 usually is untested by CI farms and in a case of personal use it's easier to wait for a fix. Hence no much reports, I suppose. > However, that means that a) is a reasonable > fix, since nobody will notice the potential performance hit either, > and it can easily be backported to wherever the breakage was > introduced. (Note that eff8728fe698, which created the problem is > marked cc:stable itself). The performance argument is questionable to me, to be honest. In practice the performance difference should be absolutely negligible for either of the proposed options, it should stay in a noise even if somebody thoroughly counting cycles, IMO. I'm still thinking that the best option will be to apply a). > Going forward, I can refine d) so that we can get rid of the kernel > mode path entirely. And then improve it using d).
On Tue, 3 Nov 2020 at 09:43, Dmitry Osipenko <digetx@gmail.com> wrote: > > 03.11.2020 10:24, Ard Biesheuvel пишет: > > Still broken today > > > > https://kernelci.org/build/id/5fa0c1a74bdb1ea4063fe7e4/ > > Still broken today https://kernelci.org/build/id/5fa898baa00b5f3167db8857/ > > So the options are > > > > a) merge my patch that adds 2 bytes of opcode to the Thumb2 build > > b) merge Dmitry's patch that adds an unconditional literal load to all builds > > c) remove kernel mode handling from vfp_support_entry() [my other patch] > > d) move sections around so that vfp_kmode_exception is guaranteed to > > be in range. > > e) do nothing > > > > Given the lack of reports about this issue, it is pretty clear that > > few people use the Thumb2 build (which I find odd, tbh, since it > > really is much smaller). > > I waited for about a month, hoping that somebody will fix this problem > before bothering with bisection, which took quite some time and effort > because intermediate commits were broken, and then with creating and > sending a patch :) > > Thumb2 usually is untested by CI farms and in a case of personal use > it's easier to wait for a fix. Hence no much reports, I suppose. > > > However, that means that a) is a reasonable > > fix, since nobody will notice the potential performance hit either, > > and it can easily be backported to wherever the breakage was > > introduced. (Note that eff8728fe698, which created the problem is > > marked cc:stable itself). > > The performance argument is questionable to me, to be honest. In > practice the performance difference should be absolutely negligible for > either of the proposed options, it should stay in a noise even if > somebody thoroughly counting cycles, IMO. > > I'm still thinking that the best option will be to apply a). > Can we take that as an acked-by? > > Going forward, I can refine d) so that we can get rid of the kernel > > mode path entirely. > > And then improve it using d).
09.11.2020 10:25, Ard Biesheuvel пишет: ... >>> So the options are >>> >>> a) merge my patch that adds 2 bytes of opcode to the Thumb2 build >>> b) merge Dmitry's patch that adds an unconditional literal load to all builds >>> c) remove kernel mode handling from vfp_support_entry() [my other patch] >>> d) move sections around so that vfp_kmode_exception is guaranteed to >>> be in range. >>> e) do nothing ... >> The performance argument is questionable to me, to be honest. In >> practice the performance difference should be absolutely negligible for >> either of the proposed options, it should stay in a noise even if >> somebody thoroughly counting cycles, IMO. >> >> I'm still thinking that the best option will be to apply a). >> > > Can we take that as an acked-by? Are you asking me for the ack? I think this is a more appropriate question to Russel. I'm not arm/ maintainer, but could give r-b and t-b. If you're going to follow approach that I'm suggesting with a) + d), then could you please resend the two patches in a single series? The first one-line patch-fix should contain the fixes tag.
On Tue, 10 Nov 2020 at 08:44, Dmitry Osipenko <digetx@gmail.com> wrote: > > 09.11.2020 10:25, Ard Biesheuvel пишет: > ... > >>> So the options are > >>> > >>> a) merge my patch that adds 2 bytes of opcode to the Thumb2 build > >>> b) merge Dmitry's patch that adds an unconditional literal load to all builds > >>> c) remove kernel mode handling from vfp_support_entry() [my other patch] > >>> d) move sections around so that vfp_kmode_exception is guaranteed to > >>> be in range. > >>> e) do nothing > ... > >> The performance argument is questionable to me, to be honest. In > >> practice the performance difference should be absolutely negligible for > >> either of the proposed options, it should stay in a noise even if > >> somebody thoroughly counting cycles, IMO. > >> > >> I'm still thinking that the best option will be to apply a). > >> > > > > Can we take that as an acked-by? > > Are you asking me for the ack? Yes. > I think this is a more appropriate > question to Russel. I'm not arm/ maintainer, but could give r-b and t-b. > R-b and acked-by are basically the same thing. > If you're going to follow approach that I'm suggesting with a) + d), > then could you please resend the two patches in a single series? The > first one-line patch-fix should contain the fixes tag. Ok
diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S index 4fcff9f59947..6e2b29f0c48d 100644 --- a/arch/arm/vfp/vfphw.S +++ b/arch/arm/vfp/vfphw.S @@ -82,7 +82,8 @@ ENTRY(vfp_support_entry) ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions and r3, r3, #MODE_MASK @ are supported in kernel mode teq r3, #USR_MODE - bne vfp_kmode_exception @ Returns through lr + ldr r1, =vfp_kmode_exception + bxne r1 @ Returns through lr VFPFMRX r1, FPEXC @ Is the VFP enabled? DBGSTR1 "fpexc %08x", r1
The vfp_kmode_exception() function now is unreachable using relative branching in THUMB2 kernel configuration, resulting in a "relocation truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'" linker error. Let's use long jump in order to fix the issue. Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") Signed-off-by: Dmitry Osipenko <digetx@gmail.com> --- arch/arm/vfp/vfphw.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)