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

[Alexey Budankov]

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;
>