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cmd/internal/obj/x86: mark 2-instruction TLS access nonpreemptible 

The 2-instruction TLS access sequence
	MOVQ TLS, BX
	MOVQ 0(BX)(TLS*1), BX
is not async preemptible, as if it is preempted and resumed on a
different thread, the TLS address may become invalid.

May fix #35349. (This is a rare failure and I haven't been able
to reproduce it.)

Change-Id: Ie1a366fd0d7d73627dc62ee2de01c0aa09365f2b
Reviewed-on: https://go-review.googlesource.com/c/go/+/206903
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Cherry Zhang 2019-11-13 15:05:17 -05:00
parent 03c58c9dcc
commit 498eaee461
1 changed files with 16 additions and 0 deletions
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16
src/cmd/internal/obj/x86/asm6.go
View File

@ -1984,6 +1984,22 @@ func span6(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
fmt.Printf(" rel %#.4x/%d %s%+d\n", uint32(r.Off), r.Siz, r.Sym.Name, r.Add)
}
}
// Mark nonpreemptible instruction sequences.
// The 2-instruction TLS access sequence
// MOVQ TLS, BX
// MOVQ 0(BX)(TLS*1), BX
// is not async preemptible, as if it is preempted and resumed on
// a different thread, the TLS address may become invalid.
if !CanUse1InsnTLS(ctxt) {
useTLS := func(p *obj.Prog) bool {
// Only need to mark the second instruction, which has
// REG_TLS as Index. (It is okay to interrupt and restart
// the first instruction.)
return p.From.Index == REG_TLS
}
obj.MarkUnsafePoints(ctxt, s.Func.Text, newprog, useTLS)
}
}
func instinit(ctxt *obj.Link) {