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SubjectRe: [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@gmail.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@gmail.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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