Re: [ppc64-linux]: skip linkage functions

[Daniel Jacobowitz <drow@mvista.com>]

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