runtime: add GODEBUG=gccheckmark=0/1
Previously, gccheckmark could only be enabled or disabled by calling
runtime.GCcheckmarkenable/GCcheckmarkdisable. This was a necessary
hack because GODEBUG was broken.
Now that GODEBUG works again, move control over gccheckmark to a
GODEBUG variable and remove these runtime functions. Currently,
gccheckmark is enabled by default (and will probably remain so for
much of the 1.5 development cycle).
Change-Id: I2bc6f30c21b795264edf7dbb6bd7354b050673ab
Reviewed-on: https://go-review.googlesource.com/2603
Reviewed-by: Rick Hudson <rlh@golang.org>
diff --git a/api/next.txt b/api/next.txt
index b94bda1..eb21e80 100644
--- a/api/next.txt
+++ b/api/next.txt
@@ -247,5 +247,3 @@
pkg runtime (openbsd-amd64-cgo), const EWOULDBLOCK ideal-int
pkg runtime (openbsd-amd64-cgo), const HW_NCPU = 3
pkg runtime (openbsd-amd64-cgo), const HW_NCPU ideal-int
-pkg runtime, func GCcheckmarkdisable()
-pkg runtime, func GCcheckmarkenable()
diff --git a/src/runtime/extern.go b/src/runtime/extern.go
index f295b9b..58acbb3 100644
--- a/src/runtime/extern.go
+++ b/src/runtime/extern.go
@@ -66,6 +66,12 @@
problem with allocfreetrace=1 in order to understand the type
of the badly updated word.
+ gccheckmark: setting gccheckmark=1 enables verification of the
+ garbage collector's concurrent mark phase by performing a
+ second mark pass while the world is stopped. If the second
+ pass finds a reachable object that was not found by concurrent
+ mark, the garbage collector will panic.
+
The GOMAXPROCS variable limits the number of operating system threads that
can execute user-level Go code simultaneously. There is no limit to the number of threads
that can be blocked in system calls on behalf of Go code; those do not count against
diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index bc14d22..fa59ce4 100644
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -611,14 +611,6 @@
}
}
-func GCcheckmarkenable() {
- systemstack(gccheckmarkenable_m)
-}
-
-func GCcheckmarkdisable() {
- systemstack(gccheckmarkdisable_m)
-}
-
// gctimes records the time in nanoseconds of each phase of the concurrent GC.
type gctimes struct {
sweepterm int64 // stw
diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index 4d0900a..6d2470d 100644
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -236,10 +236,7 @@
// When marking an object if the bool checkmark is true one uses the above
// encoding, otherwise one uses the bitMarked bit in the lower two bits
// of the nibble.
-var (
- checkmark = false
- gccheckmarkenable = true
-)
+var checkmark = false
// inheap reports whether b is a pointer into a (potentially dead) heap object.
// It returns false for pointers into stack spans.
@@ -559,7 +556,7 @@
continue
}
- if mheap_.shadow_enabled && debug.wbshadow >= 2 && gccheckmarkenable && checkmark {
+ if mheap_.shadow_enabled && debug.wbshadow >= 2 && debug.gccheckmark > 0 && checkmark {
checkwbshadow((*uintptr)(unsafe.Pointer(b + i)))
}
@@ -1856,7 +1853,7 @@
// bitMarked bit that is not set then we throw.
//go:nowritebarrier
func gccheckmark_m(startTime int64, eagersweep bool) {
- if !gccheckmarkenable {
+ if debug.gccheckmark == 0 {
return
}
@@ -1870,16 +1867,6 @@
}
//go:nowritebarrier
-func gccheckmarkenable_m() {
- gccheckmarkenable = true
-}
-
-//go:nowritebarrier
-func gccheckmarkdisable_m() {
- gccheckmarkenable = false
-}
-
-//go:nowritebarrier
func finishsweep_m() {
// The world is stopped so we should be able to complete the sweeps
// quickly.
@@ -1987,6 +1974,9 @@
}
if !checkmark {
+ // TODO(austin) This is a noop beceause we should
+ // already have swept everything to the current
+ // sweepgen.
finishsweep_m() // skip during checkmark debug phase.
}
@@ -2107,7 +2097,7 @@
sysFree(unsafe.Pointer(&work.spans[0]), uintptr(len(work.spans))*unsafe.Sizeof(work.spans[0]), &memstats.other_sys)
}
- if gccheckmarkenable {
+ if debug.gccheckmark > 0 {
if !checkmark {
// first half of two-pass; don't set up sweep
unlock(&mheap_.lock)
diff --git a/src/runtime/runtime1.go b/src/runtime/runtime1.go
index e6510a8..6056a8d 100644
--- a/src/runtime/runtime1.go
+++ b/src/runtime/runtime1.go
@@ -317,6 +317,7 @@
scheddetail int32
schedtrace int32
wbshadow int32
+ gccheckmark int32
}
var dbgvars = []dbgVar{
@@ -329,9 +330,13 @@
{"scheddetail", &debug.scheddetail},
{"schedtrace", &debug.schedtrace},
{"wbshadow", &debug.wbshadow},
+ {"gccheckmark", &debug.gccheckmark},
}
func parsedebugvars() {
+ // gccheckmark is enabled by default for the 1.5 dev cycle
+ debug.gccheckmark = 1
+
for p := gogetenv("GODEBUG"); p != ""; {
field := ""
i := index(p, ",")
