Re: [PATCH V5 1/3] riscv: Add perf callchain support

[Guo Ren]

We need know the values of *regs, eg: regs->sepc, regs->ra, regs->fp,
regs->sp, regs->tp

void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
   struct pt_regs *regs)
{
...
 walk_stackframe(&fr, entry);

// May be we could detect error here and print the regs' value
}

On Mon, Aug 26, 2019 at 4:03 PM Greentime Hu <green.hu@xxxxxxxxx> wrote:
>
> Hi Guo,
>
> Guo Ren <guoren@xxxxxxxxxx> æ 2019å8æ24æ éå äå8:54åéï
> >
> > Please check CONFIG_FRAME_POINTER
> >
> > 1 *frame = *((struct stackframe *)frame->fp - 1);
> > This code is origionally from riscv/kernel/stacktrace.c: walk_stackframe
> >
> > In linux/Makefile it'll involve the options for gcc to definitely
> > store ra & prev_fp in fp pointer.
> > ifdef CONFIG_FRAME_POINTER
> > KBUILD_CFLAGS += -fno-omit-frame-pointer -fno-optimize-sibling-calls
> >
> > So --call-graph fp need depends on CONFIG_FRAME_POINTER.
> >
>
> I am pretty sure CONFIG_FRAME_POINTER is Y
> # zcat /proc/config.gz |grep CONFIG_FRAME_POINTER
> CONFIG_FRAME_POINTER=y
>
> This is not going to go wrong every time, the probability of error is
> about one tenth or one quarter. randomly
> There may be some conditions that we have not considered.
>
> I add one more condition to check if it is a valid virtual address and
> it( ./perf record -e cpu-clock --call-graph fp ls) passes 1000 times
> without failure in Unleashed board based on 5.3-rc5.
> Here is my patch. Please have  a look at it. I am not sure if it is a
> good solution.
>
> diff --git a/arch/riscv/kernel/perf_callchain.c
> b/arch/riscv/kernel/perf_callchain.c
> index d75d15c13dc7..4717942435df 100644
> --- a/arch/riscv/kernel/perf_callchain.c
> +++ b/arch/riscv/kernel/perf_callchain.c
> @@ -18,6 +18,8 @@ static int unwind_frame_kernel(struct stackframe *frame)
>                 return -EPERM;
>         if (frame->fp < CONFIG_PAGE_OFFSET)
>                 return -EPERM;
> +       if (!virt_addr_valid(frame->fp))
> +               return -EPERM;
>
>         *frame = *((struct stackframe *)frame->fp - 1);
>         if (__kernel_text_address(frame->ra)) {
>
> It could catch cases called in this way.
>
> [ 1381.936586] frame->fp=:ffffffff00547550
> [ 1382.038542] CPU: 1 PID: 135 Comm: ls Not tainted
> 5.3.0-rc5-00003-gb008f6bcd67c-dirty #14
> [ 1382.307440] Call Trace:
> [ 1382.388947] [<ffffffe0002a2d8e>] walk_stackframe+0x0/0x9a
> [ 1382.568053] [<ffffffe0002a2f5a>] show_stack+0x2a/0x34
> [ 1382.735960] [<ffffffe00083dcd6>] dump_stack+0x62/0x7c
> [ 1382.903863] [<ffffffe0002a49e0>] perf_callchain_kernel+0xd8/0x102
> [ 1383.106558] [<ffffffe000340a6e>] get_perf_callchain+0x136/0x1f2
> [ 1383.303128] [<ffffffe00033d480>] perf_callchain+0x52/0x6e
> [ 1383.482553] [<ffffffe00033d50a>] perf_prepare_sample+0x6e/0x476
> [ 1383.679357] [<ffffffe00033d92e>] perf_event_output_forward+0x1c/0x50
> [ 1383.890633] [<ffffffe000338b4c>] __perf_event_overflow+0x6a/0xa4
> [ 1384.090279] [<ffffffe000338c40>] perf_swevent_hrtimer+0xba/0x106
> [ 1384.290094] [<ffffffe0002f307c>] __hrtimer_run_queues+0x84/0x108
> [ 1384.489694] [<ffffffe0002f36b8>] hrtimer_interrupt+0xca/0x1ce
> [ 1384.680974] [<ffffffe00072f572>] riscv_timer_interrupt+0x32/0x3a
> [ 1384.880449] [<ffffffe000854b34>] do_IRQ+0x64/0xbe
> [ 1385.036698] [<ffffffe0002a1c5c>] ret_from_exception+0x0/0xc
>
> [13915.697989] frame->fp=:fffffffffffff000
> [13915.799937] CPU: 2 PID: 663 Comm: ls Not tainted
> 5.3.0-rc5-00003-gb008f6bcd67c-dirty #14
> [13916.068832] Call Trace:
> [13916.150380] [<ffffffe0002a2d8e>] walk_stackframe+0x0/0x9a
> [13916.329450] [<ffffffe0002a2f5a>] show_stack+0x2a/0x34
> [13916.497360] [<ffffffe00083dcd6>] dump_stack+0x62/0x7c
> [13916.665265] [<ffffffe0002a49e0>] perf_callchain_kernel+0xd8/0x102
> [13916.867949] [<ffffffe000340a6e>] get_perf_callchain+0x136/0x1f2
> [13917.064526] [<ffffffe00033d480>] perf_callchain+0x52/0x6e
> [13917.243950] [<ffffffe00033d50a>] perf_prepare_sample+0x6e/0x476
> [13917.440759] [<ffffffe00033d92e>] perf_event_output_forward+0x1c/0x50
> [13917.652021] [<ffffffe000338b4c>] __perf_event_overflow+0x6a/0xa4
> [13917.851683] [<ffffffe000338c40>] perf_swevent_hrtimer+0xba/0x106
> [13918.051494] [<ffffffe0002f307c>] __hrtimer_run_queues+0x84/0x108
> [13918.251094] [<ffffffe0002f36b8>] hrtimer_interrupt+0xca/0x1ce
> [13918.442379] [<ffffffe00072f572>] riscv_timer_interrupt+0x32/0x3a
> [13918.641840] [<ffffffe000854b34>] do_IRQ+0x64/0xbe
> [13918.798082] [<ffffffe0002a1c5c>] ret_from_exception+0x0/0xc



-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/