Re: [PATCH] ARM64: perf: support dwarf unwinding in compat mode

From: Will Deacon
Date: Fri Jan 17 2014 - 05:08:14 EST

On Fri, Jan 17, 2014 at 09:00:09AM +0000, Jean Pihet wrote:
> On 16 January 2014 14:47, Jean Pihet <jean.pihet@xxxxxxxxxx> 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

> 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.

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