Re: Basic STT_GNU_IFUNC question(s)

[Richard Sandiford <rdsandiford at googlemail dot com>]

Jack Carter <Jack.Carter@imgtec.com> writes:
> Hi,
>
> I've been trying to do the MIPs port for IFUNC based on the ARM port and keep
> stumbling.
>
> For a pure shared object with just the defining ifunc routines, there seems to
> be neither .iplt stubs nor R_ARM_IRELATIVE relocations which leads me to
> believe that ld.so upon loading runs the function pointed to by the
> STT_GNU_IFUNC dynamic symbol and updates its tables from the resulting address.
>
> Is this true or have I missed something?

Yeah, it's true.

> If that is true, then what triggers ld.so to behave differently for this case?

In the ARM case we can use a PLT, so it gets done by the elf_ifunc_invoke
call in _dl_fixup.  I would have expected the same to be true for MIPS
if you're using -mplt.  But remember that MIPS has its own traditional
lazy-binding stubs, which use a different routine (dl-trampoline.c:
__dl_runtime_resolve).  You'll need to add similar code there.

You also need to call elf_ifunc_invoke in the MIPS elf_machine_rel and
elf_machine_rela functions.

Richard