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>
diff --git a/src/cmd/internal/obj/x86/asm6.go b/src/cmd/internal/obj/x86/asm6.go
index 3a33bc3..cfeb179 100644
--- a/src/cmd/internal/obj/x86/asm6.go
+++ b/src/cmd/internal/obj/x86/asm6.go
@@ -1984,6 +1984,22 @@
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) {
