Re: [Libunwind-devel] vdso and libunwind

[Lassi Tuura]

Hi,

>> Did you look at the ia64 version of libunwind?  It does handle VDSO.  
>> Frankly, I don't remember the details off hand, but if it doesn't make sense 
>> to you, let me know and I'll refresh my memory.
> 
> I didn't before, but did now. It's a good example - except that it uses 
> getunwind() which appears to be ia64-only syscall. The man page points me to 
> look at AT_SYSINFO_EHDR, so assuming I can lay my hands somehow on the auxv, 
> it should be possible grab this. Will investigate. Thanks, this was useful!

Muttering to myself:

On x86_64 linux AT_SYSINFO_EHDR is in /proc/self/auxv starting with kernel 
2.6.23. I understood GLIBC handles this automatically. Our RHEL5 kernels don't 
have it - which begs the question what I ran into originally. Turns out I was 
looking at vsyscall page (vgettimeofday, vtime), not vdso (__vdso_gettimeofday).

On x86_64 linux vsyscall page seems to be given by <asm/vsyscall.h> which 
defines VSYSCALL_{START,END,SIZE}. As far as I know even GLIBC just hard-codes 
the values. I'll try to add handling for this, and will try to find a system 
which has vdso just to make sure it gets handled correctly too.

Regards,
Lassi