Re: Wrong Perf Backtraces

On Freitag, 27. März 2020 13:58:33 CET ahmadkhorrami wrote:
> Hi,
> Thanks Milian. So if I am right, I should do the following:
> 1) Run "perf buildid-list" and catch all the <file path, build-ids>
> pairs.
> 2) First check for the existence of the file path.
> 3) If failed, concatenate "~/.debug", file path, "/" and buildid and use
> it as the alternative.

you missed the trailing "/elf" but otherwise yes :)

> I thought that GDB is smart enough to detect these situations in the
> same way that it detects debug info files.
> Should I check any directory other than ~/.debug?

Hmm good point, GDB should indeed do that by default but maybe it doesn't do 
it for the `file` command for some reason? I cannot answer this, sorry.

Cheers

> On 2020-03-27 16:40, Milian Wolff wrote:
> > On Freitag, 27. März 2020 12:04:20 CET ahmadkhorrami wrote:
> >> I do the following:
> >> If this line is in the perf script backtrace:
> >> 7f21ffe256db g_main_context_iteration+0x2b
> >> (/usr/lib/x86_64-linux-gnu/libglib-2.0.so.0.5600.4)
> >> I run the following command:
> >> gdb -batch -ex 'file
> >> /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0.5600.4'
> >> -ex 'disass g_main_context_iteration'.
> > 
> > You can try to parse the output of `perf buildid-list` to get a mapping
> > that
> > can be used to run this on another person's machine. E.g.
> > 
> > ```
> > $ perf buildid-list
> > 5837b1e7495db791f9a3a56fb6ca29958da75b0c [kernel.kallsyms]
> > 845f98f6a3019620c37a2f611b2f20c27de83d5b
> > /home/milian/projects/kdab/rnd/
> > hotspot/build/tests/test-clients/cpp-parallel/cpp-parallel
> > f6ca5853dae87d9f0503a9ef230f6d1fa15a832d /usr/lib/ld-2.30.so
> > 92883b06055e8e21ded8eb0cd5a61f5704531152 [vdso]
> > 8b04d1825b63d9a600e3d57ac71058935e7ad757 /usr/lib/libpthread-2.30.so
> > 09639b80a8fad179004f2484608764d2b336dd4a /usr/lib/libstdc++.so.6.0.27
> > 33d1f350f13728651d74dd2a56bad1e4e4648f5e /usr/lib/libc-2.30.so
> > $ file
> > ~/.debug/usr/lib/ld-2.30.so/f6ca5853dae87d9f0503a9ef230f6d1fa15a832d/
> > elf
> > /home/milian/.debug/usr/lib/ld-2.30.so/
> > f6ca5853dae87d9f0503a9ef230f6d1fa15a832d/elf: ELF 64-bit LSB shared
> > object,
> > x86-64, version 1 (SYSV), statically linked,
> > BuildID[sha1]=f6ca5853dae87d9f0503a9ef230f6d1fa15a832d, not stripped
> > ```
> > 
> > I'm afraid to say that I currently don't have the time required to be
> > of more
> > help in debugging this issue in general.
> > 
> > Good luck!


-- 
Milian Wolff | [email protected] | Senior Software Engineer
KDAB (Deutschland) GmbH, a KDAB Group company
Tel: +49-30-521325470
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