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SubjectRe: [PATCH] tracing: use %pF in trace_dump_stack()
On Tue,  9 May 2017 10:50:04 +0200
Vegard Nossum <vegard.nossum@oracle.com> wrote:

> When using trace_dump_stack() you currently just get a list of function
> names.
>
> It can be very useful to know exactly where a call came from, especially
> if there are multiple calls from one function to another.
>
> By switching trace_dump_stack() to use %pF we get the function name and
> the offset, which can also be further processed to give exact line number
> information, like this:
>
> <...>-1087 3.... 3270529us : <stack trace>
> => pty_write+0x45/0x50
> => n_tty_write+0x358/0x470
> => tty_write+0x189/0x2f0
> => __vfs_write+0x23/0x120
> => vfs_write+0xb3/0x1b0
> => SyS_write+0x44/0xa0
> => entry_SYSCALL_64_fastpath+0x18/0xad
>
> $ scripts/faddr2line vmlinux tty_write+0x189/0x2f0
> tty_write+0x189/0x2f0:
> do_tty_write at drivers/tty/tty_io.c:1174
> (inlined by) tty_write at drivers/tty/tty_io.c:1257

I prefer not to see it by default. If you want to see it:

echo 1 > /sys/kernel/debug/tracing/options/sym-offset

NACK.

-- Steve

>
> Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
> ---
> kernel/trace/trace_output.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index 02a4aeb22c47..879909efed33 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -1073,9 +1073,7 @@ static enum print_line_t trace_stack_print(struct trace_iterator *iter,
> if (trace_seq_has_overflowed(s))
> break;
>
> - trace_seq_puts(s, " => ");
> - seq_print_ip_sym(s, *p, flags);
> - trace_seq_putc(s, '\n');
> + trace_seq_printf(s, " => %pF\n", (void *) *p);
> }
>
> return trace_handle_return(s);

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