runtime: add GODEBUG for stack barriers at every frame
Currently enabling the debugging mode where stack barriers are
installed at every frame requires recompiling the runtime. However,
this is potentially useful for field debugging and for runtime tests,
so make this mode a GODEBUG.
Updates #12238.
Change-Id: I6fb128f598b19568ae723a612e099c0ed96917f5
Reviewed-on: https://go-review.googlesource.com/13947
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/src/runtime/extern.go b/src/runtime/extern.go
index d346362..cdb66ba 100644
--- a/src/runtime/extern.go
+++ b/src/runtime/extern.go
@@ -47,6 +47,9 @@
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 f7fd4e5..82b12b6 100644
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -133,18 +133,7 @@
_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 @@
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 650d038..44f9512 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -341,7 +341,7 @@
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 a50e5b6..134c999 100644
--- a/src/runtime/runtime1.go
+++ b/src/runtime/runtime1.go
@@ -310,6 +310,7 @@
gcpacertrace int32
gcshrinkstackoff int32
gcstackbarrieroff int32
+ gcstackbarrierall int32
gcstoptheworld int32
gctrace int32
invalidptr int32
@@ -327,6 +328,7 @@
{"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 @@
if islibrary || isarchive {
traceback_cache |= 1
}
+
+ if debug.gcstackbarrierall > 0 {
+ firstStackBarrierOffset = 0
+ }
}
// Poor mans 64-bit division.
