linux-kernel - Re: [PATCH v1]: perf/x86: store user space frame-pointer value on a sample

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Message-ID: <df5f38d8-9b35-0309-527a-c7b7b35c635b@linux.intel.com>
Date:   Fri, 6 Apr 2018 22:06:26 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1]: perf/x86: store user space frame-pointer value on a
 sample

On 06.04.2018 18:31, Andi Kleen wrote:
>> diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
>> index e47b2dbbdef3..9284048cf5b0 100644
>> --- a/arch/x86/kernel/perf_regs.c
>> +++ b/arch/x86/kernel/perf_regs.c
>> @@ -157,6 +157,15 @@ void perf_get_regs_user(struct perf_regs *regs_user,
>>  	 */
>>  	regs_user_copy->bx = -1;
>>  	regs_user_copy->bp = -1;
>> +	if (user_64bit_mode(user_regs)) {
> 
> Why is it 64bit only? Should work on 32bit too.

bp register is a part of i386 syscall ABI 
(http://man7.org/linux/man-pages/man2/syscall.2.html) 
so not sure if it will make any sense for 32bit processes. 

-Alexey

> 
> -Andi
> 
>> +		/*
>> +		 * Store user space frame-pointer value on sample
>> +		 * to facilitate stack unwinding for cases when
>> +		 * user space x86_64 executable code has such
>> +		 * support enabled at compile time;
>> +		 */
>> +		regs_user_copy->bp = user_regs->bp;
>> +	}
>>  	regs_user_copy->r12 = -1;
>>  	regs_user_copy->r13 = -1;
>>  	regs_user_copy->r14 = -1;
>