| Message ID | CAFrcx1=eAHsGZDsedGvvNai7Vrnf5p8RKLGFPS+cn5yGp7UQJw@mail.gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Jan 16, 2014 at 12:26:53PM +0000, Jean Pihet wrote: > On 16 January 2014 12:56, Will Deacon <will.deacon@arm.com> wrote: > > In your previous series, compat backtracing is actually split out into a > > separate function (compat_user_backtrace), so it would be more consistent to > > have a compat_user_stack_pointer macro, rather than add this check here. > > Do you mean this change instead? I don't think so... > diff --git a/kernel/events/internal.h b/kernel/events/internal.h > index 569b2187..9b88d2e 100644 > --- a/kernel/events/internal.h > +++ b/kernel/events/internal.h > @@ -185,7 +185,8 @@ static inline bool arch_perf_have_user_stack_dump(void) > return true; > } > > -#define perf_user_stack_pointer(regs) user_stack_pointer(regs) > +#define perf_user_stack_pointer(regs) \ > + (!compat_user_mode(regs)) ? ((regs)->sp) : ((regs)->compat_sp) This doesn't belong in core code; compat_user_mode and the fields of regs are arm64-specific. So I suppose you need to rework your original patch to call compat_user_stack_pointer (which we already define in compat.h for arm64) if compat_user_mode(regs)). The problem there is the inconsistency with respect to the regs argument: user_stack_pointer(regs) // Returns user stack pointer for regs current_user_stack_pointer() // Returns current user stack pointer compat_user_stack_pointer() // Doesn't take a regs argument! On top of that, x86 treats those last two functions differently when current is a compat task. So the simplest thing would be to make compat_user_stack_pointer expand to user_stack_pointer(current_pt_regs()) on arm64 and merge that in with your original patch fixing user_stack_pointer. Will
Will, On 16 January 2014 13:57, Will Deacon <will.deacon@arm.com> wrote: > On Thu, Jan 16, 2014 at 12:26:53PM +0000, Jean Pihet wrote: >> On 16 January 2014 12:56, Will Deacon <will.deacon@arm.com> wrote: >> > In your previous series, compat backtracing is actually split out into a >> > separate function (compat_user_backtrace), so it would be more consistent to >> > have a compat_user_stack_pointer macro, rather than add this check here. The compat_user_backtrace function is used to unwind using the frame pointer, it is not used to unwind using the dwarf info (which uses the user stack pointer). >> >> Do you mean this change instead? > > I don't think so... > >> diff --git a/kernel/events/internal.h b/kernel/events/internal.h >> index 569b2187..9b88d2e 100644 >> --- a/kernel/events/internal.h >> +++ b/kernel/events/internal.h >> @@ -185,7 +185,8 @@ static inline bool arch_perf_have_user_stack_dump(void) >> return true; >> } >> >> -#define perf_user_stack_pointer(regs) user_stack_pointer(regs) >> +#define perf_user_stack_pointer(regs) \ >> + (!compat_user_mode(regs)) ? ((regs)->sp) : ((regs)->compat_sp) > > This doesn't belong in core code; compat_user_mode and the fields of regs > are arm64-specific. Right. > So I suppose you need to rework your original patch to > call compat_user_stack_pointer (which we already define in compat.h for > arm64) if compat_user_mode(regs)). The perf core code calls perf_user_stack_pointer(regs) to retrieve the stack pointer, with perf_user_stack_pointer(regs) defined as user_stack_pointer(regs). The problem is that perf is not aware of the compat mode, so every arch has to implement user_stack_pointer(regs) correctly. For this reason I think the first patch proposal is the right one unless the perf core code is redesigned to handle different ABIs. Do you see a better implementation? > > The problem there is the inconsistency with respect to the regs argument: > > user_stack_pointer(regs) // Returns user stack pointer for regs > current_user_stack_pointer() // Returns current user stack pointer > compat_user_stack_pointer() // Doesn't take a regs argument! > > On top of that, x86 treats those last two functions differently when current > is a compat task. > > So the simplest thing would be to make compat_user_stack_pointer expand to > user_stack_pointer(current_pt_regs()) on arm64 and merge that in with your > original patch fixing user_stack_pointer. > > Will Thx! Jean
Hi Will, Some more thoughts below On 16 January 2014 14:47, Jean Pihet <jean.pihet@linaro.org> wrote: > Will, > > On 16 January 2014 13:57, Will Deacon <will.deacon@arm.com> wrote: >> On Thu, Jan 16, 2014 at 12:26:53PM +0000, Jean Pihet wrote: >>> On 16 January 2014 12:56, Will Deacon <will.deacon@arm.com> wrote: >>> > In your previous series, compat backtracing is actually split out into a >>> > separate function (compat_user_backtrace), so it would be more consistent to >>> > have a compat_user_stack_pointer macro, rather than add this check here. > The compat_user_backtrace function is used to unwind using the frame > pointer, it is not used to unwind using the dwarf info (which uses the > user stack pointer). > >>> >>> Do you mean this change instead? >> >> I don't think so... >> >>> diff --git a/kernel/events/internal.h b/kernel/events/internal.h >>> index 569b2187..9b88d2e 100644 >>> --- a/kernel/events/internal.h >>> +++ b/kernel/events/internal.h >>> @@ -185,7 +185,8 @@ static inline bool arch_perf_have_user_stack_dump(void) >>> return true; >>> } >>> >>> -#define perf_user_stack_pointer(regs) user_stack_pointer(regs) >>> +#define perf_user_stack_pointer(regs) \ >>> + (!compat_user_mode(regs)) ? ((regs)->sp) : ((regs)->compat_sp) >> >> This doesn't belong in core code; compat_user_mode and the fields of regs >> are arm64-specific. > Right. > >> So I suppose you need to rework your original patch to >> call compat_user_stack_pointer (which we already define in compat.h for >> arm64) if compat_user_mode(regs)). > The perf core code calls perf_user_stack_pointer(regs) to retrieve the > stack pointer, with perf_user_stack_pointer(regs) defined as > user_stack_pointer(regs). > The problem is that perf is not aware of the compat mode, so every > arch has to implement user_stack_pointer(regs) correctly. > > For this reason I think the first patch proposal is the right one > unless the perf core code is redesigned to handle different ABIs. Do > you see a better implementation? > >> >> The problem there is the inconsistency with respect to the regs argument: >> >> user_stack_pointer(regs) // Returns user stack pointer for regs >> current_user_stack_pointer() // Returns current user stack pointer >> compat_user_stack_pointer() // Doesn't take a regs argument! >> >> On top of that, x86 treats those last two functions differently when current >> is a compat task. >> >> So the simplest thing would be to make compat_user_stack_pointer expand to >> user_stack_pointer(current_pt_regs()) on arm64 and merge that in with your >> original patch fixing user_stack_pointer. I see 2 issues in your proposal: 1) user_stack_pointer(regs) calls compat_user_stack_pointer if compat_user_mode(regs)) and compat_user_stack_pointer expands to user_stack_pointer. I see a circular dependency in the macros. 2) current_pt_regs() returns the current task regs although perf passes a regs struct that had been recorded previously. Am I missing something? Thx, Jean >> >> Will > > Thx! > Jean
On Fri, Jan 17, 2014 at 09:00:09AM +0000, Jean Pihet wrote: > On 16 January 2014 14:47, Jean Pihet <jean.pihet@linaro.org> wrote: > >> So the simplest thing would be to make compat_user_stack_pointer expand to > >> user_stack_pointer(current_pt_regs()) on arm64 and merge that in with your > >> original patch fixing user_stack_pointer. > > I see 2 issues in your proposal: > > 1) user_stack_pointer(regs) calls compat_user_stack_pointer if > compat_user_mode(regs)) and compat_user_stack_pointer expands to > user_stack_pointer. I see a circular dependency in the macros. Not today it doesn't, so you just need to avoid writing the circular dependency and instead make user_stack_pointer access (regs)->compat_sp instead. > 2) current_pt_regs() returns the current task regs although perf > passes a regs struct that had been recorded previously. Yes, but compat_user_stack_pointer doesn't take a regs paramater anyway, so there's no change in behaviour here. Will
diff --git a/kernel/events/internal.h b/kernel/events/internal.h index 569b2187..9b88d2e 100644 --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -185,7 +185,8 @@ static inline bool arch_perf_have_user_stack_dump(void) return true; } -#define perf_user_stack_pointer(regs) user_stack_pointer(regs) +#define perf_user_stack_pointer(regs) \ + (!compat_user_mode(regs)) ? ((regs)->sp) : ((regs)->compat_sp) #else static inline bool arch_perf_have_user_stack_dump(void) {