On Thu, Apr 25, 2019 at 4:42 AM Masahiro Yamada <[email protected]> wrote: > > Hi Andy, > > On Sat, Jun 21, 2014 at 4:23 AM Andy Lutomirski <[email protected]> wrote: > > > > With this change, doing 'make vdso_install' and telling gdb: > > > > set debug-file-directory /lib/modules/KVER/vdso > > > > will enable vdso debugging with symbols. This is useful for > > testing, but kernel RPM builds will probably want to manually delete > > these symlinks or otherwise do something sensible when they strip > > the vdso/*.so files. > > > > If ld does not support --build-id, then the symlinks will not be > > created. > > > > Note that kernel packagers that use vdso_install may need to adjust > > their packaging scripts to accomdate this change. For example, > > Fedora's scripts create build-id symlinks themselves in a different > > location, so the spec should probably be updated to remove the > > symlinks created by make vdso_install. > > > > Signed-off-by: Andy Lutomirski <[email protected]> > > --- > > I was looking into this, but > I am not familiar enough with this area. > > > Could you tell me how it works? > > > I use Ubuntu 18.04 LTS. > Luckily, it has build-id symlinks by default, > so I should be able to test it easily. > > > > masahiro@pug:~$ uname -r > 4.15.0-47-generic > masahiro@pug:~$ cd /lib/modules/4.15.0-47-generic/vdso/ > masahiro@pug:/lib/modules/4.15.0-47-generic/vdso$ file vdso64.so > vdso64.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), > dynamically linked, > BuildID[sha1]=d742540fb9ded5c3650dbe9ae20c0f39e386464c, with > debug_info, not stripped > masahiro@pug:/lib/modules/4.15.0-47-generic/vdso$ ls -l > .build-id/d7/42540fb9ded5c3650dbe9ae20c0f39e386464c.debug > lrwxrwxrwx 1 root root 15 Mar 13 13:37 > .build-id/d7/42540fb9ded5c3650dbe9ae20c0f39e386464c.debug -> > ../../vdso64.so > > > I dumped the vdso embedded in the kernel, > and I confirmed its build-id matches > to the one of unstripped vdso. > > > So, I expect the vdso with symbol info will be automatically loaded > by setting debug-file-directory to /lib/modules/4.15.0-47-generic/vdso. > Am I right? > > If it works as expected, how should it look like? > > I started gdb like this: > > $ gdb date > > Then, I did: > > (gdb) set debug-file-directory > /usr/lib/debug:/lib/modules/4.15.0-47-generic/vdso > (gdb) show debug-file-directory > The directory where separate debug symbols are searched for is > "/usr/lib/debug:/lib/modules/4.15.0-47-generic/vdso". > (gdb) run > > > The list of shared library looks like follows: > > > (gdb) info sharedlibrary > From To Syms Read Shared Object Library > 0x00007ffff7dd5f10 0x00007ffff7df4b20 Yes > /lib64/ld-linux-x86-64.so.2 > 0x00007ffff7a052d0 0x00007ffff7b7dc3c Yes > /lib/x86_64-linux-gnu/libc.so.6 > No linux-vdso.so.1 > > > > The first two shared objects shows "Yes" because debug info > is available under /usr/lib/debug/lib/x86_64-linux-gnu/ > and associated by .gnu_debuglink. > > > linux-vdso.so.1 shows "No". > Does it mean no symbol was included ? >
It's been a long time since I've looked at this, and I don't remember all the details. I think your best bet may be to run gdb under strace and to try to figure out what it's doing.
