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

* 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.

> +
> +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.

> +
> 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.

> + 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?

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

Thanks,

Ingo


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