cmd/link: generate PPC64 ABI register save/restore functions if needed

They are usually needed when internally linking gcc code
compiled with -Os. These are typically generated by ld
or gold, but are missing when linking internally.

The PPC64 ELF ABI describes a set of functions to save/restore
non-volatile, callee-save registers using R1/R0/R12:

 _savegpr0_n: Save Rn-R31 relative to R1, save LR (in R0), return
 _restgpr0_n: Restore Rn-R31 from R1, and return to saved LR
  _savefpr_n: Save Fn-F31 based on R1, and save LR (in R0), return
  _restfpr_n: Restore Fn-F31 from R1, and return to 16(R1)
 _savegpr1_n: Save Rn-R31 based on R12, return
 _restgpr1_n: Restore Rn-R31 based on R12, return
   _savevr_m: Save VRm-VR31 based on R0, R12 is scratch, return
   _restvr_m: Restore VRm-VR31 based on R0, R12 is scratch, return

 m is a value 20<=m<=31
 n is a value 14<=n<=31

Add several new functions similar to those suggested by the
PPC64 ELFv2 ABI. And update the linker to scan external relocs
for these calls, and redirect them to runtime.elf_<func>+offset
in runtime/asm_ppc64x.go.

Similarly, code which generates plt stubs is moved into
a dedicated function. This avoids an extra scan of relocs.

fixes #52336

Change-Id: I2f0f8b5b081a7b294dff5c92b4b1db8eba9a9400
Reviewed-on: https://go-review.googlesource.com/c/go/+/400796
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Paul Murphy <murp@ibm.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

0 files changed, 0 insertions, 0 deletions