Re: [PATCH -tip 6/7] perf bts trace: print function+offset

Frederic Weisbecker
2010-12-06T02:42:52Z

On Fri, Dec 03, 2010 at 01:00:15PM +0900, Akihiro Nagai wrote:
> Provide the function to print function+offset.
> And, set it as the default behavior of 'perf bts trace'.
> To use this function, users can also specify the option '-s' or '--symbol'.
>
> Example: 'perf bts -as trace'
> This command prints address and function+offset.
>
> Output sample:
> address function+offset
> 0xffffffff8146fe0e irq_return+0x0 => 0x00007fd4038e3b20 _start+0x0
> ...
> 0x000000380661ee79 __libc_start_main+0xf9 => 0x00000000004035c3 main+0x0
> 0xffffffff8146ef4e irq_return+0x0 => 0x00000000004035c3 main+0x0
> 0x00000000004035e8 main+0x25 => 0x000000000040bca0 set_program_name+0x0
> 0xffffffff8146ef4e irq_return+0x0 => 0x000000000040bca0 set_program_name+0x0
> 0x000000000040bcae set_program_name+0xe => 0x00000000004023d0 strrchr@plt+0x0
> 0x00000000004023d0 strrchr@plt+0x0 => 0x00000000004023d6 strrchr@plt+0x6
> ...
> 0x0000000000403e0c main+0x849 => 0x00000000004021f0 exit@plt+0x0
> 0x00000000004021f0 exit@plt+0x0 => 0x00000000004021f6 exit@plt+0x6
> 0x00000000004021fb exit@plt+0xb => 0x00000000004020d0 _init+0x18
> 0x00000000004020d6 _init+0x1e => 0x00000038062149d0 _dl_runtime_resolve+0x0
> ...

There is another kind of mode that I suspect would be very useful: something like
a userspace function graph tracer (you can have a look into the kernel function
graph tracer we have in ftrace to get an overview).

So, the idea would be to rebuild the whole function call flow:

main() {
func1()
func2() {
func3()
}
}

This would require to deref the instructions into the dso addresses from
the bts trace, keep only the "call" and the "ret" (there would be a small arch
backend for this mode) and rebuild the whole tree of calls.
We already have all the dso address mapping API in place with perf.

I really think this could be a very useful tool. Also we can even later
expand this to the branches, as Peter suggested. But starting with calls
would a very great start already.

Thanks.