Re: Symbols not found for some files

[Paul Menzel]

Dear Arnaldo,


Am 03.10.2018 um 22:57 schrieb Arnaldo Carvalho de Melo:
> Em Wed, Oct 03, 2018 at 10:42:39PM +0200, Paul Menzel escreveu:

> > For profiling the boot on my Debian Sid/unstable system (32-bit user space),
> > the following service unit is used.
>
> You forgot to mention what is the version of the perf tool in that
> system, so that I could check if this got fixed somehow after that
> version.
>
> Can you please provide it?

Sorry for not mentioning it. I built it from Linusâ Linux master branch.

    $ perf --version
    perf version 4.19.rc5.gd7887c


Kind regards,

Paul


> > ```
> > $ systemctl cat perf
> > # /etc/systemd/system/perf.service
> >
> > [Unit]
> > Description=Perf 10 s
> > DefaultDependencies=no
> >
> > [Service]
> > ExecStart=/usr/local/bin/perf record -F 999 -g -a -o /dev/shm/perf.data
> > sleep 10
> >
> > [Install]
> > WantedBy=sysinit.target
> > ```
> >
> > Running `perf.data` through `perf script`, the messages below are shown.
> >
> > ```
> > [vdso] with build id 69dd0f0c522f0d3e2a87722d70245ab9725c8b42 not found,
> > continuing without symbols
> > /lib/systemd/libsystemd-shared-239.so with build id
> > 196c7922a15fa971d68775522dd16e82da46ebb3 not found, continuing without
> > symbols
> > /lib/systemd/systemd-journald with build id
> > 9e31591e8c9bb88de06e96a251f34d8a7e201f6c not found, continuing without
> > symbols
> > /lib/systemd/systemd with build id 1b92f342a959b6ff370b82092bfadaf1d470a7b9
> > not found, continuing without symbols
> > /lib/systemd/systemd-networkd with build id
> > 9fa8f6abc1f2e5c1018d0a33be058c22e25efaff not found, continuing without
> > symbols
> > /lib/systemd/systemd-logind with build id
> > 63d664b5f8f8e85274aff6730ec9e924d74c8fed not found, continuing without
> > symbols
> > ```
> >
> > But, the debug symbol packages are installed (`systemd-dbgsym`), and GDB
> > loads the debug symbols just fine.
> >
> > ```
> > $ gdb --quiet /lib/systemd/libsystemd-shared-239.so
> > Reading symbols from /lib/systemd/libsystemd-shared-239.so...Reading symbols
> > from /usr/lib/debug/.build-id/19/6c7922a15fa971d68775522dd16e82da46ebb3.debug...done.
> > done.
> > (gdb)
> > ```
> >
> > Tracing `perf`, it also seems to find them, but does not use them.
> >
> > ```
> > stat64("/home/kodi/.debug/.build-id/a2/03af6935d5ab00f79fe12b4098d27d3f70c19f",
> > 0xbfbd54ac) = -1 ENOENT (No such file or directory)
> > stat64("/home/kodi/.debug/.build-id/a2/03af6935d5ab00f79fe12b4098d27d3f70c19f/elf",
> > 0xbfbd75bc) = -1 ENOENT (No such file or directory)
> > stat64("03af6935d5ab00f79fe12b4098d27d3f70c19f.debug", 0xbfbd1bfc) = -1
> > ENOENT (No such file or directory)
> > stat64("/lib/i386-linux-gnu/03af6935d5ab00f79fe12b4098d27d3f70c19f.debug",
> > 0xbfbd1bfc) = -1 ENOENT (No such file or directory)
> > stat64("/lib/i386-linux-gnu/.debug/03af6935d5ab00f79fe12b4098d27d3f70c19f.debug",
> > 0xbfbd1bfc) = -1 ENOENT (No such file or directory)
> > stat64("/usr/lib/debug/lib/i386-linux-gnu/03af6935d5ab00f79fe12b4098d27d3f70c19f.debug",
> > 0xbfbd1bfc) = -1 ENOENT (No such file or directory)
> > stat64("/home/kodi/.debug/.build-id/a2/03af6935d5ab00f79fe12b4098d27d3f70c19f",
> > 0xbfbd1b5c) = -1 ENOENT (No such file or directory)
> > stat64("/home/kodi/.debug/.build-id/a2/03af6935d5ab00f79fe12b4098d27d3f70c19f/elf",
> > 0xbfbd3c6c) = -1 ENOENT (No such file or directory)
> > stat64("/home/kodi/.debug/.build-id/a2/03af6935d5ab00f79fe12b4098d27d3f70c19f",
> > 0xbfbd1b5c) = -1 ENOENT (No such file or directory)
> > stat64("/home/kodi/.debug/.build-id/a2/03af6935d5ab00f79fe12b4098d27d3f70c19f/debug",
> > 0xbfbd3c6c) = -1 ENOENT (No such file or directory)
> > stat64("/usr/lib/debug/.build-id/a2/03af6935d5ab00f79fe12b4098d27d3f70c19f.debug",
> > {st_mode=S_IFREG|0644, st_size=4524336, ...}) = 0
> > openat(AT_FDCWD,
> > "/usr/lib/debug/.build-id/a2/03af6935d5ab00f79fe12b4098d27d3f70c19f.debug",
> > O_RDONLY|O_LARGEFILE) = 91
> > ```
> >
> > Looking into `perf` with GDB, the code in `util/symbol.c` below is not
> > setting `runtime_ss`, because `symsrc__possibly_runtime(ss)` returns false.
> > Then the for loop is not quit, and continues.
> >
> > ```
> >                  if (!syms_ss && symsrc__has_symtab(ss)) {
> >                          syms_ss = ss;
> >                          next_slot = true;
> >                          if (!dso->symsrc_filename)
> >                                  dso->symsrc_filename = strdup(name);
> >                  }
> >
> >                  if (!runtime_ss && symsrc__possibly_runtime(ss)) {
> >                          runtime_ss = ss;
> >                          next_slot = true;
> >                  }
> >
> >                  if (next_slot) {
> >                          ss_pos++;
> >
> >                          if (syms_ss && runtime_ss)
> >                                  break;
> >                  } else {
> >                          symsrc__destroy(ss);
> >                  }
> >
> > ```
> >
> > Do you have an idea, why the files from the systemd Debian package cause
> > problems for `perf` but not GDB? The Debian maintainers mentioned, that LTO
> > is enabled for the Debian package.
> >
> > Please tell me, if you need other information to look into the problem.
> >
> >
> > Kind regards,
> >
> > Paul