Re: vdso

[Jan Kratochvil <jan.kratochvil@redhat.com>]

On Wed, 03 Jul 2013 10:34:43 +0200, vijay nag wrote:
> cat /proc/15896/smaps | grep vdso
> 778:b7fff000-b8000000 r-xp b7fff000 00:00 0          [vdso]
> 
> Does vdso come with symbols ?

For basic ELF symbols it does. Try:
	dump memory /tmp/vdso.so 0xb7fff000 0xb8000000
	readelf -Ws /tmp/vdso.so

and .dynsym section there should contain the symbols:
     4: ffffffffff700ba0   404 FUNC    GLOBAL DEFAULT   15 __vdso_gettimeofday@@LINUX_2.6
     5: ffffffffff700d60    61 FUNC    GLOBAL DEFAULT   15 __vdso_getcpu@@LINUX_2.6
etc.

Then there are also DWARF symbols to see even filenames / line numbers but
those .debug_* sections at least Fedora ships only on disk in kernel-debuginfo
rpm. The symbols get loaded automatically by GDB:
lrwxrwxrwx 1 root root 61 Jul  2 00:43 /usr/lib/debug/.build-id/92/0bba09195bde2b45a7a4eaec1dc78c3157c0f5 -> ../../../../../lib/modules/3.9.8-200.fc18.x86_64/vdso/vdso.so*
lrwxrwxrwx 1 root root 58 Jul  2 00:43 /usr/lib/debug/.build-id/92/0bba09195bde2b45a7a4eaec1dc78c3157c0f5.debug -> ../../lib/modules/3.9.8-200.fc18.x86_64/vdso/vdso.so.debug
-rwxr-xr-x 1 root root   4856 Jun 28 16:56 /lib/modules/3.9.8-200.fc18.x86_64/vdso/vdso.so*
-r--r--r-- 1 root root 104848 Jun 28 16:56 /usr/lib/debug/lib/modules/3.9.8-200.fc18.x86_64/vdso/vdso.so.debug
$ rpm -qf /lib/modules/3.9.8-200.fc18.x86_64/vdso/vdso.so /usr/lib/debug/lib/modules/3.9.8-200.fc18.x86_64/vdso/vdso.so.debug
kernel-3.9.8-200.fc18.x86_64
kernel-debuginfo-3.9.8-200.fc18.x86_64


You should check first /tmp/vdso.so to see whether your Linux kernel or GDB is
the problem.


Jan