sync/atomic: update comment for ARM 64-bit atomics

They don't work on older chips, just like the x86-32 64-bit atomics.

Update #6134

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/12880043

diff --git a/src/pkg/sync/atomic/doc.go b/src/pkg/sync/atomic/doc.go
index 4651e2e8c2b752468a6f26faa9c6388afbf287a8..34a2bc1390b2f258f35770576b8fb7ee40ee8cc4 100644 (file)
--- a/src/pkg/sync/atomic/doc.go
+++ b/src/pkg/sync/atomic/doc.go
@@ -47,6 +47,8 @@ import (
 
 // BUG(rsc): On x86-32, the 64-bit functions use instructions unavailable before the Pentium MMX.
 //
+// On non-Linux ARM, the 64-bit functions use instructions unavailable before the ARMv6k core.
+//
 // On both ARM and x86-32, it is the caller's responsibility to arrange for 64-bit
 // alignment of 64-bit words accessed atomically. The first word in a global
 // variable or in an allocated struct or slice can be relied upon to be