Re: [RFC][PATCH] linux-2.6.2-rc2_vsyscall-gtod_B1.patch

[Jamie Lokier <jamie@shareable.org>]

Ulrich Drepper wrote:
> ~ alternatively use the symbol table the vdso has.  Export the new code
> only via the symbol table.  No fixed address for the function, the
> runtime gets it from the symbol table.  glibc will use weak symbol
> references; if the symbol isn't there, the old code is used.  This will
> require that every single optimized syscall needs to be handled special.
> 
> 
> I personally like the first approach better.  The indirection table can
> maintained in sync with the syscall table inside the kernel.  It all
> comes at all times from the same source.  The overhead of the memory
> load should be neglectable.

I like the second approach more.  You can change glibc to look up the
weak symbol for _all_ syscalls, then none of them are special and it
will work with future kernel optimisations.

-- Jamie