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