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| author | Austin Clements <austin@google.com> | 2017-10-22 21:37:05 -0400 |
|---|---|---|
| committer | Austin Clements <austin@google.com> | 2017-10-29 17:56:08 +0000 |
| commit | 3beaf26e4fbf1bfd166fc3b5b7584a58b11e726c (patch) | |
| tree | e48654f465fb74c541abea00c94d0ea8420c3bfb /src/runtime/asm_s390x.s | |
| parent | ca0f303f2b332aa19b80e1b9ea4fc3c6e3b8aeb7 (diff) | |
| download | go-3beaf26e4fbf1bfd166fc3b5b7584a58b11e726c.tar.gz go-3beaf26e4fbf1bfd166fc3b5b7584a58b11e726c.zip | |
runtime: remove write barriers from newstack, gogo
Currently, newstack and gogo have write barriers for maintaining the
context register saved in g.sched.ctxt. This is troublesome, because
newstack can be called from go:nowritebarrierrec places that can't
allow write barriers. It happens to be benign because g.sched.ctxt
will always be nil on entry to newstack *and* it so happens the
incoming ctxt will also always be nil in these contexts (I
think/hope), but this is playing with fire. It's also desirable to
mark newstack go:nowritebarrierrec to prevent any other, non-benign
write barriers from creeping in, but we can't do that right now
because of this one write barrier.
Fix all of this by observing that g.sched.ctxt is really just a saved
live pointer register. Hence, we can shade it when we scan g's stack
and otherwise move it back and forth between the actual context
register and g.sched.ctxt without write barriers. This means we can
save it in morestack along with all of the other g.sched, eliminate
the save from newstack along with its troublesome write barrier, and
eliminate the shenanigans in gogo to invoke the write barrier when
restoring it.
Once we've done all of this, we can mark newstack
go:nowritebarrierrec.
Fixes #22385.
For #22460.
Change-Id: I43c24958e3f6785b53c1350e1e83c2844e0d1522
Reviewed-on: https://go-review.googlesource.com/72553
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Diffstat (limited to 'src/runtime/asm_s390x.s')
| -rw-r--r-- | src/runtime/asm_s390x.s | 18 |
1 files changed, 3 insertions, 15 deletions
diff --git a/src/runtime/asm_s390x.s b/src/runtime/asm_s390x.s index 241be17842..524b866b21 100644 --- a/src/runtime/asm_s390x.s +++ b/src/runtime/asm_s390x.s @@ -116,17 +116,6 @@ TEXT runtime·gosave(SB), NOSPLIT, $-8-8 // restore state from Gobuf; longjmp TEXT runtime·gogo(SB), NOSPLIT, $16-8 MOVD buf+0(FP), R5 - - // If ctxt is not nil, invoke deletion barrier before overwriting. - MOVD gobuf_ctxt(R5), R1 - CMPBEQ R1, $0, nilctxt - MOVD $gobuf_ctxt(R5), R1 - MOVD R1, 8(R15) - MOVD R0, 16(R15) - BL runtime·writebarrierptr_prewrite(SB) - MOVD buf+0(FP), R5 - -nilctxt: MOVD gobuf_g(R5), g // make sure g is not nil BL runtime·save_g(SB) @@ -272,7 +261,7 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0 MOVD LR, R8 MOVD R8, (g_sched+gobuf_pc)(g) MOVD R5, (g_sched+gobuf_lr)(g) - // newstack will fill gobuf.ctxt. + MOVD R12, (g_sched+gobuf_ctxt)(g) // Called from f. // Set m->morebuf to f's caller. @@ -285,9 +274,8 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0 BL runtime·save_g(SB) MOVD (g_sched+gobuf_sp)(g), R15 // Create a stack frame on g0 to call newstack. - MOVD $0, -16(R15) // Zero saved LR in frame - SUB $16, R15 - MOVD R12, 8(R15) // ctxt argument + MOVD $0, -8(R15) // Zero saved LR in frame + SUB $8, R15 BL runtime·newstack(SB) // Not reached, but make sure the return PC from the call to newstack |