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

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Date:	Thu, 16 Jan 2014 11:56:34 +0000
From:	Will Deacon <will.deacon@....com>
To:	Jean Pihet <jean.pihet@...aro.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Arnaldo <acme@...stprotocols.net>,
	"patches@...aro.org" <patches@...aro.org>,
	Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] ARM64: perf: support dwarf unwinding in compat mode

Hi Jean,

On Thu, Jan 16, 2014 at 10:45:23AM +0000, Jean Pihet wrote:
> Add support for unwinding using the dwarf information in compat
> mode. Using the correct user stack pointer allows perf to record
> the frames correctly in the native and compat modes.
> 
> Note that although the dwarf frame unwinding works ok using
> libunwind in native mode (on ARMv7 & ARMv8), some changes are
> required to the libunwind code for the compat mode. Those changes
> are posted separately on the libunwind mailing list.
> 
> Tested on ARMv8 platform with v8 and compat v7 binaries, the latter
> are statically built.

I guess it makes sense to include this with your earlier series adding
support for compat backtracing?

> Signed-off-by: Jean Pihet <jean.pihet@...aro.org>
> ---
>  arch/arm64/include/asm/ptrace.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> 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)

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.

Will
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