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SubjectRe: [PATCH] ARM64: perf: support dwarf unwinding in compat mode
On Mon, Jan 20, 2014 at 05:05:14PM +0000, Jean Pihet wrote:
> Hi Will,
>
> Here is an updated version of the change, which uses compat_sp at only
> one place.
> The drawback is that compat_user_mode is checked when calling
> compat_user_stack_pointer, which seems unnecessary. Unfortunately the
> check is not optimized out by the complier as I could check with
> objdump -S.
>
> What do you think?

I think that's cleaner and really wouldn't worry about the couple of extra
instructions.

Cheers,

Will

> diff --git a/arch/arm64/include/asm/compat.h b/arch/arm64/include/asm/compat.h
> index fda2704..e71f81f 100644
> --- a/arch/arm64/include/asm/compat.h
> +++ b/arch/arm64/include/asm/compat.h
> @@ -228,7 +228,7 @@ static inline compat_uptr_t ptr_to_compat(void __user *uptr)
> return (u32)(unsigned long)uptr;
> }
>
> -#define compat_user_stack_pointer() (current_pt_regs()->compat_sp)
> +#define compat_user_stack_pointer() (user_stack_pointer(current_pt_regs()))
>
> static inline void __user *arch_compat_alloc_user_space(long len)
> {
> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
> index fbb0020..86d5b54 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -133,7 +133,7 @@ struct pt_regs {
> (!((regs)->pstate & PSR_F_BIT))
>
> #define user_stack_pointer(regs) \
> - ((regs)->sp)
> + (!compat_user_mode(regs)) ? ((regs)->sp) : ((regs)->compat_sp)
>
> /*
> * Are the current registers suitable for user mode? (used to maintain


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