From 3873e5497d21979910a1ec7cf90a34577fa1f6ae Mon Sep 17 00:00:00 2001 From: Cherry Zhang Date: Sun, 20 Oct 2019 17:23:02 -0400 Subject: [PATCH] runtime: don't async preempt NO_LOCAL_POINTERS assembly functions We don't async preempt assembly functions. We do that by checking whether the function has a local pointer map, and assume it is an assembly (or, non-Go) function if there isn't one. However, assembly functions marked with NO_LOCAL_POINTERS still have local pointer maps, and we wouldn't identify them. For them, check for the special pointer map runtime.no_pointers_stackmap as well, and treat them as not async preemptible. Change-Id: I1301e3b4d35893c31c4c5a5147a0d775987bd6f4 Reviewed-on: https://go-review.googlesource.com/c/go/+/202337 Reviewed-by: Austin Clements --- src/runtime/preempt.go | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/src/runtime/preempt.go b/src/runtime/preempt.go index 71c3089830..544c251a9f 100644 --- a/src/runtime/preempt.go +++ b/src/runtime/preempt.go @@ -55,6 +55,7 @@ package runtime import ( "runtime/internal/atomic" "runtime/internal/sys" + "unsafe" ) type suspendGState struct { @@ -369,9 +370,12 @@ func isAsyncSafePoint(gp *g, pc, sp uintptr) bool { // functions (except at calls). return false } - if funcdata(f, _FUNCDATA_LocalsPointerMaps) == nil { + if fd := funcdata(f, _FUNCDATA_LocalsPointerMaps); fd == nil || fd == unsafe.Pointer(&no_pointers_stackmap) { // This is assembly code. Don't assume it's - // well-formed. + // well-formed. We identify assembly code by + // checking that it has either no stack map, or + // no_pointers_stackmap, which is the stack map + // for ones marked as NO_LOCAL_POINTERS. // // TODO: Are there cases that are safe but don't have a // locals pointer map, like empty frame functions? @@ -395,3 +399,5 @@ func isAsyncSafePoint(gp *g, pc, sp uintptr) bool { return true } + +var no_pointers_stackmap uint64 // defined in assembly, for NO_LOCAL_POINTERS macro -- 2.50.0