Re: [ppc64-linux]: skip linkage functions

Daniel Jacobowitz
2003-06-06T13:11:28Z

On Fri, Jun 06, 2003 at 01:22:27AM -0500, Jim Blandy wrote:
> Daniel Jacobowitz <drow@mvista.com> writes:
>
> > On Thu, Jun 05, 2003 at 06:54:57PM -0500, Jim Blandy wrote:
> > >
> > > 2003-06-05 Jim Blandy <jimb@redhat.com>
> > >
> > > Recognize and skip 64-bit PowerPC Linux linkage functions.
> > > * ppc-linux-tdep.c (insn_d, insn_ds, insn_xfx, read_insn, struct
> > > insn_pattern, insns_match_pattern, d_field, ds_field): New
> > > functions, macros, and types for working with PPC instructions.
> > > (ppc64_standard_linkage, PPC64_STANDARD_LINKAGE_LEN,
> > > ppc64_in_solib_call_trampoline, ppc64_standard_linkage_target,
> > > ppc64_skip_trampoline_code): New functions, variables, and macros
> > > for recognizing and skipping linkage functions.
> > > (ppc_linux_init_abi): Use ppc64_in_solib_call_trampoline and
> > > ppc64_skip_trampoline_code for the 64-bit PowerPC Linux ABI.
> >
> > Hmm. Probably not good enough for our needs, but is the
> > DW_AT_trampoline attribute useful here?
>
> I'll say it, so nobody else has to feel bad saying it: that patch is
> complete shite. I just can't see any other way to do it with the info
> I have.
>
> DW_AT_trampoline would allow me to implement in_solib_call_trampoline
> and skip_trampoline_code simply by consulting the debugging info,
> which would be eons better. And in generic code, to boot. The only
> thing is, the trampolines are generated by the linker, not the
> compiler. Could the linker contribute its own Dwarf compilation unit
> to .debug_info and .debug_abbrev? How should it decide which
> debugging format to use, and whether to emit anything at all?
>
> If we could get this working, we could start using it on other
> architectures, too.

Hmm. I believe it could be done. It would probably require adding
a --gdwarf2 to the linker, matching the one added to GAS. It's
certainly practical for the linker to add a CU.

As always, it wouldn't free us from the need to grub through assembly
trampolines by hand. There's always something without debug info. But
it would make that code a little less important...

--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer