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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_arm.s | |
| parent | ca0f303f2b332aa19b80e1b9ea4fc3c6e3b8aeb7 (diff) | |
| download | go-3beaf26e4fbf1bfd166fc3b5b7584a58b11e726c.tar.xz | |
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_arm.s')
| -rw-r--r-- | src/runtime/asm_arm.s | 18 |
1 files changed, 2 insertions, 16 deletions
diff --git a/src/runtime/asm_arm.s b/src/runtime/asm_arm.s index 47fa565c52..caa96cc4b3 100644 --- a/src/runtime/asm_arm.s +++ b/src/runtime/asm_arm.s @@ -227,19 +227,6 @@ TEXT runtime·gosave(SB),NOSPLIT,$-4-4 // restore state from Gobuf; longjmp TEXT runtime·gogo(SB),NOSPLIT,$8-4 MOVW buf+0(FP), R1 - - // If ctxt is not nil, invoke deletion barrier before overwriting. - MOVW gobuf_ctxt(R1), R0 - CMP $0, R0 - B.EQ nilctxt - MOVW $gobuf_ctxt(R1), R0 - MOVW R0, 4(R13) - MOVW $0, R0 - MOVW R0, 8(R13) - BL runtime·writebarrierptr_prewrite(SB) - MOVW buf+0(FP), R1 - -nilctxt: MOVW gobuf_g(R1), R0 BL setg<>(SB) @@ -412,7 +399,7 @@ TEXT runtime·morestack(SB),NOSPLIT,$-4-0 MOVW R13, (g_sched+gobuf_sp)(g) MOVW LR, (g_sched+gobuf_pc)(g) MOVW R3, (g_sched+gobuf_lr)(g) - // newstack will fill gobuf.ctxt. + MOVW R7, (g_sched+gobuf_ctxt)(g) // Called from f. // Set m->morebuf to f's caller. @@ -426,8 +413,7 @@ TEXT runtime·morestack(SB),NOSPLIT,$-4-0 BL setg<>(SB) MOVW (g_sched+gobuf_sp)(g), R13 MOVW $0, R0 - MOVW.W R0, -8(R13) // create a call frame on g0 - MOVW R7, 4(R13) // ctxt argument + MOVW.W R0, -4(R13) // create a call frame on g0 (saved LR) BL runtime·newstack(SB) // Not reached, but make sure the return PC from the call to newstack |