[release-branch.go1.14] cmd/compile, runtime: mark R12 clobbered for write barrier call on PPC64
When external linking, for large binaries, the external linker
may insert a trampoline for the write barrier call, which looks
0000000005a98cc8 <__long_branch_runtime.gcWriteBarrier>:
5a98cc8: 86 01 82 3d addis r12,r2,390
5a98ccc: d8 bd 8c e9 ld r12,-16936(r12)
5a98cd0: a6 03 89 7d mtctr r12
5a98cd4: 20 04 80 4e bctr
It clobbers R12 (and CTR, which is never live across a call).
As at compile time we don't know whether the binary is big and
what link mode will be used, I think we need to mark R12 as
clobbered for write barrier call. For extra safety (future-proof)
we mark caller-saved register that cannot be used for function
arguments, which includes R11, as potentially clobbered as well.
Updates #40851.
Fixes #40938.
Change-Id: Iedd901c5072f1127cc59b0a48cfeb4aaec81b519
Reviewed-on: https://go-review.googlesource.com/c/go/+/248917
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
(cherry picked from commit
b58d29741650c7bf10b17f455666e2727e1cdd2e)
Reviewed-on: https://go-review.googlesource.com/c/go/+/249697