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runtime: don't async preempt NO_LOCAL_POINTERS assembly functions

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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 <austin@google.com>
This commit is contained in:
Cherry Zhang 2019-10-20 17:23:02 -04:00 committed by Austin Clements
parent 7955ecebfc
commit 3873e5497d
1 changed files with 8 additions and 2 deletions
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10
src/runtime/preempt.go
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@ -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