linux-kernel - Re: [PATCH] perf: x86: fix callgraphs of 32-bit processes on 64-bit kernels V2.

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Date:	Wed, 17 Mar 2010 10:48:54 +0200
From:	Török Edwin <edwintorok@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: x86: fix callgraphs of 32-bit processes on 64-bit
 kernels V2.

On 03/16/2010 07:05 PM, Ingo Molnar wrote:
> * T??r??k Edwin <edwintorok@...il.com> wrote:
> 
>> When profiling a 32-bit process on a 64-bit kernel, callgraph tracing
>> stopped after the first function, because it has seen a garbage memory address
>> (tried to interpret the frame pointer, and return address as a 64-bit pointer).
>>
>> Fix this by using a struct stack_frame with 32-bit pointers when the TIF_IA32 flag is set.
>>
>> Note that TIF_IA32 flag must be used, and not is_compat_task(), because the
>> latter is only set when the 32-bit process is executing a syscall,
>> which may not always be the case (when tracing page fault events for example).
>>
>> Signed-off-by: T??r??k Edwin <edwintorok@...il.com>
>> ---
>>  arch/x86/kernel/cpu/perf_event.c |   33 +++++++++++++++++++++++++++++++++
>>  1 files changed, 33 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
>> index 8c1c070..b85ea9f 100644
>> --- a/arch/x86/kernel/cpu/perf_event.c
>> +++ b/arch/x86/kernel/cpu/perf_event.c
>> @@ -2401,6 +2401,20 @@ static int copy_stack_frame(const void __user *fp, struct stack_frame *frame)
>>  	return bytes == sizeof(*frame);
>>  }
>>  
>> +struct stack_frame_ia32 {
>> +    u32 next_frame;
>> +    u32 return_address;
>> +};
> 
> Please put such new data type definitions not into the middle of a .c file but 
> next to where struct stack_frame is defined.

Ok.

> 
>> +
>> +static int copy_stack_frame_ia32(u32 fp, struct stack_frame_ia32 *frame)
>> +{
>> +	unsigned long bytes;
>> +
>> +	bytes = copy_from_user_nmi(frame, (const void __user*)(unsigned long)fp, sizeof(*frame));
>> +
>> +	return bytes == sizeof(*frame);
>> +}
>>
> 
> Single-use - should be inline i guess.
> 

So should be copy_stack_frame() then.

>> +
>>  static void
>>  perf_callchain_user(struct pt_regs *regs, struct perf_callchain_entry *entry)
>>  {
>> @@ -2414,6 +2428,25 @@ perf_callchain_user(struct pt_regs *regs, struct perf_callchain_entry *entry)
>>  
>>  	callchain_store(entry, PERF_CONTEXT_USER);
>>  	callchain_store(entry, regs->ip);
>> +	if (test_thread_flag(TIF_IA32)) {
>> +	    /* 32-bit process in 64-bit kernel. */
>> +	    u32 fp = regs->bp;
>> +	    struct stack_frame_ia32 frame;
>> +	    while (entry->nr < PERF_MAX_STACK_DEPTH) {
> 
> Please put newlines after local variable definition so that they are clearly 
> delimited.
> 
> Also, the tabulation is weird - please run it through scripts/checkpatch.pl.

I forgot to change shiftwidth to 8 (I usually use 4).
I cleaned the checkpatch warnings now.

> 
>> +		frame.next_frame     = 0;
>> +		frame.return_address = 0;
>> +
>> +		if (!copy_stack_frame_ia32(fp, &frame))
>> +			break;
>> +
>> +		if (fp < (u32)regs->sp)
>> +			break;
>> +
>> +		callchain_store(entry, frame.return_address);
>> +		fp = frame.next_frame;
>> +	    }
>> +	    return;
> 
> This whole new block should probably be in a helper inline?

To reduce indenting, or why?

> 
> Also, it should probably be #ifdef CONFIG_COMPAT or so.

Ok, see V3 of my patch.

Best regards,
--Edwin
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