Re: [PATCH] perf dso: Fix dso comparison

[Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>]

Em Tue, Mar 24, 2020 at 10:00:52AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Tue, Mar 24, 2020 at 11:48:43AM +0100, Jiri Olsa escreveu:
> > On Tue, Mar 24, 2020 at 09:54:24AM +0530, Ravi Bangoria wrote:
> > > Perf gets dso details from two different sources. 1st, from builid
> > > headers in perf.data and 2nd from MMAP2 samples. Dso from buildid
> > > header does not have dso_id detail. And dso from MMAP2 samples does
> > > not have buildid information. If detail of the same dso is present
> > > at both the places, filename is common.
> > > 
> > > Previously, __dsos__findnew_link_by_longname_id() used to compare only
> > > long or short names, but Commit 0e3149f86b99 ("perf dso: Move dso_id
> > > from 'struct map' to 'struct dso'") also added a dso_id comparison.
> > > Because of that, now perf is creating two different dso objects of the
> > > same file, one from buildid header (with dso_id but without buildid)
> > > and second from MMAP2 sample (with buildid but without dso_id).
> > > 
> > > This is causing issues with archive, buildid-list etc subcommands. Fix
> > > this by comparing dso_id only when it's present. And incase dso is
> > > present in 'dsos' list without dso_id, inject dso_id detail as well.
> > > 
> > > Before:
> > > 
> > >   $ sudo ./perf buildid-list -H
> > >   0000000000000000000000000000000000000000 /usr/bin/ls
> > >   0000000000000000000000000000000000000000 /usr/lib64/ld-2.30.so
> > >   0000000000000000000000000000000000000000 /usr/lib64/libc-2.30.so
> > > 
> > >   $ ./perf archive
> > >   perf archive: no build-ids found
> > > 
> > > After:
> > > 
> > >   $ ./perf buildid-list -H
> > >   b6b1291d0cead046ed0fa5734037fa87a579adee /usr/bin/ls
> > >   641f0c90cfa15779352f12c0ec3c7a2b2b6f41e8 /usr/lib64/ld-2.30.so
> > >   675ace3ca07a0b863df01f461a7b0984c65c8b37 /usr/lib64/libc-2.30.so
> > > 
> > >   $ ./perf archive
> > >   Now please run:
> > > 
> > >   $ tar xvf perf.data.tar.bz2 -C ~/.debug
> > > 
> > >   wherever you need to run 'perf report' on.

This improves the situation, but something else is still amiss:

[root@five ~]# perf buildid-list -H | grep ^000000000000 | while read -a line ; do path=${line[1]} ; nlines=$(perf buildid-list -H -i perf.data | grep $path | tee /tmp/lines | wc -l) ;[ $nlines -eq 2 ] && cat /tmp/lines ; done
641f0c90cfa15779352f12c0ec3c7a2b2b6f41e8 /usr/lib64/ld-2.30.so
0000000000000000000000000000000000000000 /usr/lib64/ld-2.30.so
d40c8da7371d8adea464ae2b099590b2c4465574 /usr/lib64/libpthread-2.30.so
0000000000000000000000000000000000000000 /usr/lib64/libpthread-2.30.so
aec38b95c2b305c9f1943b2dd988aeb58c17a5d9 /usr/lib64/libm-2.30.so
0000000000000000000000000000000000000000 /usr/lib64/libm-2.30.so
675ace3ca07a0b863df01f461a7b0984c65c8b37 /usr/lib64/libc-2.30.so
0000000000000000000000000000000000000000 /usr/lib64/libc-2.30.so
8286f22591b0be26730eea306a22a0f30475590b /usr/bin/bash
0000000000000000000000000000000000000000 /usr/bin/bash
[root@five ~]#

I.e. DSOs that have not changed:

[root@five ~]# grep libpthread /proc/*/maps | cut -d' ' -f6- | sort  | uniq -c
    690                    /usr/lib64/libpthread-2.30.so
[root@five ~]#

[root@five ~]# file /usr/lib64/libpthread-2.30.so
/usr/lib64/libpthread-2.30.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=d40c8da7371d8adea464ae2b099590b2c4465574, for GNU/Linux 3.2.0, not stripped
[root@five ~]#
[root@five ~]# perf buildid-list -i /usr/lib64/libpthread-2.30.so
d40c8da7371d8adea464ae2b099590b2c4465574
[root@five ~]#

Appear with/without build-id in 'perf buildid-list'.

I'm checking a bit more to see if I figure this out, I'll keep your
patch in, maybe this is a diferent issue, will combine if needed.

- Arnaldo