Messages in this thread | | | Date | Tue, 16 Mar 2010 17:04:34 +0200 | From | Török Edwin <> | Subject | Re: [PATCH] perf: x86: fix callgraphs of 32-bit processes on 64-bit kernels. |
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On 03/16/2010 04:49 PM, Frederic Weisbecker wrote: > On Mon, Mar 15, 2010 at 05:34:20PM +0200, Török Edwin 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: Török 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..13ee83a 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; >> +}; >> + >> +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); >> +} >> + >> 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) { >> + frame.next_frame = 0; >> + frame.return_address = 0; >> + >> + if (!copy_stack_frame_ia32(fp, &frame)) >> + break; >> + >> + if ((unsigned long)fp < regs->sp) >> + break; > > > > Shouldn't it be this? > > if (fp < (u32)regs->sp) > > As the high part of fp is zeroed in the cast but > the high part of regs->sp remains. I don't know what could be > there, but since the user doesn't use it, perhaps just garbage? > And that could messup the comparison.
Agreed. I sent a new patch with that change.
> > Otherwise the rest looks pretty good to me, nice catch. >
Thanks.
Best regards, --Edwin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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