| Message ID | 1312971223-28165-6-git-send-email-dave.martin@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, 2011-08-10 at 11:13 +0100, Dave Martin wrote: > +#if __LINUX_ARM_ARCH__ < 7 > +/* If the target CPU may not be Thumb-2-capable, a run-time check is needed: */ > +#define NEED_CPU_ARCHITECTURE > + ldr r5, .LCcpu_architecture > + ldr r5, [r5] > + cmp r5, #CPU_ARCH_ARMv7 > + blo __und_usr_unknown > +/* > + * The following code won't get run unless the running CPU really is v7, so > + * coding round the lack of ldrht on older arches is pointless. Temporarily > + * override the assembler target arch with the minimum required instead: > + */ > + .arch armv6t2 > +#endif > 2: > ARM( ldrht r5, [r4], #2 ) > THUMB( ldrht r5, [r4] ) > @@ -449,7 +470,16 @@ __und_usr: > 3: ldrht r0, [r4] > add r2, r2, #2 @ r2 is PC + 2, make it PC + 4 > orr r0, r0, r5, lsl #16 > + > +#if __LINUX_ARM_ARCH__ < 7 > +/* If the target arch was overridden, change it back: */ > +#ifdef CONFIG_CPU_32v6K > + .arch armv6k > #else > + .arch armv6 > +#endif Are we confident that there will be no other v6 architectures supported in future? Looks like a bit of a hazard otherwise. Looking at the assembler manual, MIPS and PowerPC have push/pop operations for changing things like arch settings, pity ARM doesn't.
On Wed, Aug 10, 2011 at 12:55:52PM +0100, Tixy wrote: > On Wed, 2011-08-10 at 11:13 +0100, Dave Martin wrote: > > +#if __LINUX_ARM_ARCH__ < 7 > > +/* If the target CPU may not be Thumb-2-capable, a run-time check is needed: */ > > +#define NEED_CPU_ARCHITECTURE > > + ldr r5, .LCcpu_architecture > > + ldr r5, [r5] > > + cmp r5, #CPU_ARCH_ARMv7 > > + blo __und_usr_unknown > > +/* > > + * The following code won't get run unless the running CPU really is v7, so > > + * coding round the lack of ldrht on older arches is pointless. Temporarily > > + * override the assembler target arch with the minimum required instead: > > + */ > > + .arch armv6t2 > > +#endif > > 2: > > ARM( ldrht r5, [r4], #2 ) > > THUMB( ldrht r5, [r4] ) > > @@ -449,7 +470,16 @@ __und_usr: > > 3: ldrht r0, [r4] > > add r2, r2, #2 @ r2 is PC + 2, make it PC + 4 > > orr r0, r0, r5, lsl #16 > > + > > +#if __LINUX_ARM_ARCH__ < 7 > > +/* If the target arch was overridden, change it back: */ > > +#ifdef CONFIG_CPU_32v6K > > + .arch armv6k > > #else > > + .arch armv6 > > +#endif > > Are we confident that there will be no other v6 architectures supported > in future? Looks like a bit of a hazard otherwise. More or less. armv6Z is theoretically possible, but highly unlikely to affect this file. armv6T2 is only rarely deployed and has not gone upstream. Neither __LINUX_ARM_ARCH__ nor cpu_architecture has a value corresponding to this architecture. Without CONFIG_THUMB2_KERNEL, I think assembling entry-armv.S will just work as-is; with CONFIG_THUMB2_KERNEL there would be build failures, giving someone an opportunity to fix it. Since v6T2 would only happen in some specialised niches anyway, it's less likely that someone would be building this into a combined kernel, even if it were supported. An alternative route is to change arch/arm/Makefile to pass a command-line #define for the "real" architecture so we can restore to it. My attempts to do that seemed at least as fragile, though... > > Looking at the assembler manual, MIPS and PowerPC have push/pop > operations for changing things like arch settings, pity ARM doesn't. There have been discussions with people (i.e., me) advocating a similar option for the assembler on ARM. I wasn't aware that it actually existed for some arches... interesting. My searches didn't find these. Unfortunately, those save/restore features seem have been done in a somewhat gross, target-specific way (maybe inherited from those targets' native assemblers) where it could profitably have been made generic... Either way, even if it gets implemented it will be some time before everyone using gas has that feature, so we can't really rely on it in ARM-land. Cheers ---Dave
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S index b7236d4..bc41ebd 100644 --- a/arch/arm/kernel/entry-armv.S +++ b/arch/arm/kernel/entry-armv.S @@ -24,6 +24,7 @@ #include <asm/unwind.h> #include <asm/unistd.h> #include <asm/tls.h> +#include <asm/system.h> #include "entry-header.S" #include <asm/entry-macro-multi.S> @@ -439,7 +440,27 @@ __und_usr: #endif beq call_fpe @ Thumb instruction -#if __LINUX_ARM_ARCH__ >= 7 +#if CONFIG_ARM_THUMB && __LINUX_ARM_ARCH__ >= 6 && CONFIG_CPU_V7 +/* + * Thumb-2 instruction handling. Note that because pre-v6 and >= v6 platforms + * can never be supported in a single kernel, this code is not applicable at + * all when __LINUX_ARM_ARCH__ < 6. This allows simplifying assumptions to be + * made about .arch directives. + */ +#if __LINUX_ARM_ARCH__ < 7 +/* If the target CPU may not be Thumb-2-capable, a run-time check is needed: */ +#define NEED_CPU_ARCHITECTURE + ldr r5, .LCcpu_architecture + ldr r5, [r5] + cmp r5, #CPU_ARCH_ARMv7 + blo __und_usr_unknown +/* + * The following code won't get run unless the running CPU really is v7, so + * coding round the lack of ldrht on older arches is pointless. Temporarily + * override the assembler target arch with the minimum required instead: + */ + .arch armv6t2 +#endif 2: ARM( ldrht r5, [r4], #2 ) THUMB( ldrht r5, [r4] ) @@ -449,7 +470,16 @@ __und_usr: 3: ldrht r0, [r4] add r2, r2, #2 @ r2 is PC + 2, make it PC + 4 orr r0, r0, r5, lsl #16 + +#if __LINUX_ARM_ARCH__ < 7 +/* If the target arch was overridden, change it back: */ +#ifdef CONFIG_CPU_32v6K + .arch armv6k #else + .arch armv6 +#endif +#endif /* __LINUX_ARM_ARCH__ < 7 */ +#else /* !(CONFIG_ARM_THUMB && __LINUX_ARM_ARCH__ >= 6 && CONFIG_CPU_V7) */ b __und_usr_unknown #endif UNWIND(.fnend ) @@ -576,6 +606,12 @@ call_fpe: movw_pc lr @ CP#14 (Debug) movw_pc lr @ CP#15 (Control) +#ifdef NEED_CPU_ARCHITECTURE + .align 2 +.LCcpu_architecture: + .word cpu_architecture +#endif + #ifdef CONFIG_NEON .align 6
When v6 and >=v7 boards are supported in the same kernel, the __und_usr code currently makes a build-time assumption that Thumb-2 instructions occurring in userspace don't need to be supported. Strictly speaking this is incorrect. This patch fixes the above case by doing a run-time check on the CPU architecture in these cases. This only affects kernels which support v6 and >=v7 CPUs together: plain v6 and plain v7 kernels are unaffected. Signed-off-by: Dave Martin <dave.martin@linaro.org> --- arch/arm/kernel/entry-armv.S | 38 +++++++++++++++++++++++++++++++++++++- 1 files changed, 37 insertions(+), 1 deletions(-)