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Re: vDSO support for 32-bit x86?
On Tue, Feb 12, 2013 at 5:14 PM, Roland McGrath <roland@hack.frob.com> wrote:
> I don't know how you could miss it. It was the first machine to have a
> vDSO. nptl/sysdeps/unix/sysv/linux/i386/i686/dl-sysdep.h defines
> NEED_DL_SYSINFO, which is the baseline of "has vDSO support".
>
> There is no i386-specific code that uses _dl_vdso_vsym, because the i386
> vDSO does not contain any interesting secondary entrypoints like several
> other machines now do. It only has the syscall entrypoint, which is found
> by the e_entry field in the vDSO's ELF header rather than by symbol lookup;
> and the signal handling trampoline, which is used directly by the kernel.
That explains it then, I was looking for much more to be implemented than
simply the subtle setting of NEED_DL_SYSINFO which triggers the use of
the vDSO.
For avoidance of doubt the reason I ask is that I've run across a couple of
use cases where 32-bit programs running on a 64-bit kernel could make use
of a faster gettimeofday. It seems like it would certainly be doable.
Cheers,
Carlos.