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cmd/compile: don't clobber dead slots in runtime.wbBufFlush

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runtime.wbBufFlush must not modify its arguments, because the
argument slots are also used as spill slots in runtime.gcWriteBarrier.
So, GOEXPERIMENT=clobberdead must not clobber them.

Updates #27326.

Change-Id: Id02bb22a45201eecee748d89e7bdb3df7e4940e4
Reviewed-on: https://go-review.googlesource.com/131957
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Cherry Zhang 2018-08-29 12:09:34 -04:00
parent c8545722a1
commit 360771e422
1 changed files with 4 additions and 1 deletions
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5
src/cmd/compile/internal/gc/plive.go
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@ -1203,13 +1203,16 @@ func (lv *Liveness) clobber() {
}
fmt.Printf("\t\t\tCLOBBERDEAD %s\n", lv.fn.funcname())
}
if lv.f.Name == "forkAndExecInChild" {
if lv.f.Name == "forkAndExecInChild" || lv.f.Name == "wbBufFlush" {
// forkAndExecInChild calls vfork (on linux/amd64, anyway).
// The code we add here clobbers parts of the stack in the child.
// When the parent resumes, it is using the same stack frame. But the
// child has clobbered stack variables that the parent needs. Boom!
// In particular, the sys argument gets clobbered.
// Note to self: GOCLOBBERDEADHASH=011100101110
//
// runtime.wbBufFlush must not modify its arguments. See the comments
// in runtime/mwbbuf.go:wbBufFlush.
return
}