4 files changed, 23 insertions, 13 deletions
diff --git a/src/runtime/extern.go b/src/runtime/extern.go
index d346362773..cdb66ba24e 100644
--- a/src/runtime/extern.go
+++ b/src/runtime/extern.go
@@ -47,6 +47,9 @@ It is a comma-separated list of name=val pairs setting these named variables:
 	that allow the garbage collector to avoid repeating a stack scan during the
 	mark termination phase.
 
+	gcstackbarrierall: setting gcstackbarrierall=1 installs stack barriers
+	in every stack frame, rather than in exponentially-spaced frames.
+
 	gcstoptheworld: setting gcstoptheworld=1 disables concurrent garbage collection,
 	making every garbage collection a stop-the-world event. Setting gcstoptheworld=2
 	also disables concurrent sweeping after the garbage collection finishes.
diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index f7fd4e51d5..82b12b6c09 100644
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -133,18 +133,7 @@ const (
 	_RootFlushCaches = 4
 	_RootCount       = 5
 
-	// firstStackBarrierOffset is the approximate byte offset at
-	// which to place the first stack barrier from the current SP.
-	// This is a lower bound on how much stack will have to be
-	// re-scanned during mark termination. Subsequent barriers are
-	// placed at firstStackBarrierOffset * 2^n offsets.
-	//
-	// For debugging, this can be set to 0, which will install a
-	// stack barrier at every frame. If you do this, you may also
-	// have to raise _StackMin, since the stack barrier
-	// bookkeeping will use a large amount of each stack.
-	firstStackBarrierOffset = 1024
-	debugStackBarrier       = false
+	debugStackBarrier = false
 
 	// sweepMinHeapDistance is a lower bound on the heap distance
 	// (in bytes) reserved for concurrent sweeping between GC
@@ -152,6 +141,18 @@ const (
 	sweepMinHeapDistance = 1024 * 1024
 )
 
+// firstStackBarrierOffset is the approximate byte offset at
+// which to place the first stack barrier from the current SP.
+// This is a lower bound on how much stack will have to be
+// re-scanned during mark termination. Subsequent barriers are
+// placed at firstStackBarrierOffset * 2^n offsets.
+//
+// For debugging, this can be set to 0, which will install a
+// stack barrier at every frame. If you do this, you may also
+// have to raise _StackMin, since the stack barrier
+// bookkeeping will use a large amount of each stack.
+var firstStackBarrierOffset = 1024
+
 // heapminimum is the minimum heap size at which to trigger GC.
 // For small heaps, this overrides the usual GOGC*live set rule.
 //
diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go
index 650d03862e..44f951269b 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -341,7 +341,7 @@ func scanstack(gp *g) {
 	switch gcphase {
 	case _GCscan:
 		// Install stack barriers during stack scan.
-		barrierOffset = firstStackBarrierOffset
+		barrierOffset = uintptr(firstStackBarrierOffset)
 		nextBarrier = sp + barrierOffset
 
 		if debug.gcstackbarrieroff > 0 {
diff --git a/src/runtime/runtime1.go b/src/runtime/runtime1.go
index a50e5b618c..134c999088 100644
--- a/src/runtime/runtime1.go
+++ b/src/runtime/runtime1.go
@@ -310,6 +310,7 @@ var debug struct {
 	gcpacertrace      int32
 	gcshrinkstackoff  int32
 	gcstackbarrieroff int32
+	gcstackbarrierall int32
 	gcstoptheworld    int32
 	gctrace           int32
 	invalidptr        int32
@@ -327,6 +328,7 @@ var dbgvars = []dbgVar{
 	{"gcpacertrace", &debug.gcpacertrace},
 	{"gcshrinkstackoff", &debug.gcshrinkstackoff},
 	{"gcstackbarrieroff", &debug.gcstackbarrieroff},
+	{"gcstackbarrierall", &debug.gcstackbarrierall},
 	{"gcstoptheworld", &debug.gcstoptheworld},
 	{"gctrace", &debug.gctrace},
 	{"invalidptr", &debug.invalidptr},
@@ -382,6 +384,10 @@ func parsedebugvars() {
 	if islibrary || isarchive {
 		traceback_cache |= 1
 	}
+
+	if debug.gcstackbarrierall > 0 {
+		firstStackBarrierOffset = 0
+	}
 }
 
 // Poor mans 64-bit division.