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Subject[PATCH] tracing: use %pF in trace_dump_stack()
Date
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

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);
--
2.12.0.rc0
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