Will, On 16 January 2014 13:57, Will Deacon <[email protected]> wrote: > On Thu, Jan 16, 2014 at 12:26:53PM +0000, Jean Pihet wrote: >> On 16 January 2014 12:56, Will Deacon <[email protected]> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
