runtime: eliminate all writebarrierptr* calls
Calls to writebarrierptr can simply be actual pointer writes. Calls to
writebarrierptr_prewrite need to go through the write barrier buffer.
Updates #22460.
Change-Id: I92cee4da98c5baa499f1977563757c76f95bf0ca
Reviewed-on: https://go-review.googlesource.com/92704
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Rick Hudson <rlh@golang.org>
diff --git a/src/runtime/atomic_pointer.go b/src/runtime/atomic_pointer.go
index 292b351..09cfbda 100644
--- a/src/runtime/atomic_pointer.go
+++ b/src/runtime/atomic_pointer.go
@@ -16,11 +16,24 @@
// Instead, these are wrappers around the actual atomics (casp1 and so on)
// that use noescape to convey which arguments do not escape.
+// atomicwb performs a write barrier before an atomic pointer write.
+// The caller should guard the call with "if writeBarrier.enabled".
+//
+//go:nosplit
+func atomicwb(ptr *unsafe.Pointer, new unsafe.Pointer) {
+ slot := (*uintptr)(unsafe.Pointer(ptr))
+ if !getg().m.p.ptr().wbBuf.putFast(*slot, uintptr(new)) {
+ wbBufFlush(slot, uintptr(new))
+ }
+}
+
// atomicstorep performs *ptr = new atomically and invokes a write barrier.
//
//go:nosplit
func atomicstorep(ptr unsafe.Pointer, new unsafe.Pointer) {
- writebarrierptr_prewrite((*uintptr)(ptr), uintptr(new))
+ if writeBarrier.enabled {
+ atomicwb((*unsafe.Pointer)(ptr), new)
+ }
atomic.StorepNoWB(noescape(ptr), new)
}
@@ -29,7 +42,9 @@
// The write barrier is only necessary if the CAS succeeds,
// but since it needs to happen before the write becomes
// public, we have to do it conservatively all the time.
- writebarrierptr_prewrite((*uintptr)(unsafe.Pointer(ptr)), uintptr(new))
+ if writeBarrier.enabled {
+ atomicwb(ptr, new)
+ }
return atomic.Casp1((*unsafe.Pointer)(noescape(unsafe.Pointer(ptr))), noescape(old), new)
}
@@ -43,7 +58,9 @@
//go:linkname sync_atomic_StorePointer sync/atomic.StorePointer
//go:nosplit
func sync_atomic_StorePointer(ptr *unsafe.Pointer, new unsafe.Pointer) {
- writebarrierptr_prewrite((*uintptr)(unsafe.Pointer(ptr)), uintptr(new))
+ if writeBarrier.enabled {
+ atomicwb(ptr, new)
+ }
sync_atomic_StoreUintptr((*uintptr)(unsafe.Pointer(ptr)), uintptr(new))
}
@@ -53,7 +70,9 @@
//go:linkname sync_atomic_SwapPointer sync/atomic.SwapPointer
//go:nosplit
func sync_atomic_SwapPointer(ptr *unsafe.Pointer, new unsafe.Pointer) unsafe.Pointer {
- writebarrierptr_prewrite((*uintptr)(unsafe.Pointer(ptr)), uintptr(new))
+ if writeBarrier.enabled {
+ atomicwb(ptr, new)
+ }
old := unsafe.Pointer(sync_atomic_SwapUintptr((*uintptr)(noescape(unsafe.Pointer(ptr))), uintptr(new)))
return old
}
@@ -64,6 +83,8 @@
//go:linkname sync_atomic_CompareAndSwapPointer sync/atomic.CompareAndSwapPointer
//go:nosplit
func sync_atomic_CompareAndSwapPointer(ptr *unsafe.Pointer, old, new unsafe.Pointer) bool {
- writebarrierptr_prewrite((*uintptr)(unsafe.Pointer(ptr)), uintptr(new))
+ if writeBarrier.enabled {
+ atomicwb(ptr, new)
+ }
return sync_atomic_CompareAndSwapUintptr((*uintptr)(noescape(unsafe.Pointer(ptr))), uintptr(old), uintptr(new))
}
diff --git a/src/runtime/chan.go b/src/runtime/chan.go
index 41ae803..678128b 100644
--- a/src/runtime/chan.go
+++ b/src/runtime/chan.go
@@ -310,6 +310,8 @@
// So make sure that no preemption points can happen between read & use.
dst := sg.elem
typeBitsBulkBarrier(t, uintptr(dst), uintptr(src), t.size)
+ // No need for cgo write barrier checks because dst is always
+ // Go memory.
memmove(dst, src, t.size)
}
diff --git a/src/runtime/hashmap_fast.go b/src/runtime/hashmap_fast.go
index 2de3814..f978d1b 100644
--- a/src/runtime/hashmap_fast.go
+++ b/src/runtime/hashmap_fast.go
@@ -1002,7 +1002,8 @@
// Copy key.
if sys.PtrSize == 4 && t.key.kind&kindNoPointers == 0 && writeBarrier.enabled {
- writebarrierptr((*uintptr)(dst.k), *(*uintptr)(k))
+ // Write with a write barrier.
+ *(*unsafe.Pointer)(dst.k) = *(*unsafe.Pointer)(k)
} else {
*(*uint32)(dst.k) = *(*uint32)(k)
}
@@ -1103,7 +1104,8 @@
// Copy key.
if t.key.kind&kindNoPointers == 0 && writeBarrier.enabled {
if sys.PtrSize == 8 {
- writebarrierptr((*uintptr)(dst.k), *(*uintptr)(k))
+ // Write with a write barrier.
+ *(*unsafe.Pointer)(dst.k) = *(*unsafe.Pointer)(k)
} else {
// There are three ways to squeeze at least one 32 bit pointer into 64 bits.
// Give up and call typedmemmove.
diff --git a/src/runtime/mbitmap.go b/src/runtime/mbitmap.go
index 3a88f17..8e03505 100644
--- a/src/runtime/mbitmap.go
+++ b/src/runtime/mbitmap.go
@@ -550,6 +550,8 @@
// make sure the underlying allocation contains pointers, usually
// by checking typ.kind&kindNoPointers.
//
+// Callers must perform cgo checks if writeBarrier.cgo.
+//
//go:nosplit
func bulkBarrierPreWrite(dst, src, size uintptr) {
if (dst|src|size)&(sys.PtrSize-1) != 0 {
@@ -649,7 +651,7 @@
}
}
-// typeBitsBulkBarrier executes writebarrierptr_prewrite for every
+// typeBitsBulkBarrier executes a write barrier for every
// pointer that would be copied from [src, src+size) to [dst,
// dst+size) by a memmove using the type bitmap to locate those
// pointer slots.
@@ -663,6 +665,8 @@
// Must not be preempted because it typically runs right before memmove,
// and the GC must observe them as an atomic action.
//
+// Callers must perform cgo checks if writeBarrier.cgo.
+//
//go:nosplit
func typeBitsBulkBarrier(typ *_type, dst, src, size uintptr) {
if typ == nil {
@@ -680,6 +684,7 @@
return
}
ptrmask := typ.gcdata
+ buf := &getg().m.p.ptr().wbBuf
var bits uint32
for i := uintptr(0); i < typ.ptrdata; i += sys.PtrSize {
if i&(sys.PtrSize*8-1) == 0 {
@@ -691,7 +696,9 @@
if bits&1 != 0 {
dstx := (*uintptr)(unsafe.Pointer(dst + i))
srcx := (*uintptr)(unsafe.Pointer(src + i))
- writebarrierptr_prewrite(dstx, *srcx)
+ if !buf.putFast(*dstx, *srcx) {
+ wbBufFlush(nil, 0)
+ }
}
}
}
