3 files changed, 36 insertions, 2 deletions
diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go
index 714b9a51df..f58b98bd7f 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -967,6 +967,11 @@ func scanstack(gp *g, gcw *gcWork) int64 {
 		scanblock(uintptr(unsafe.Pointer(&gp.sched.ctxt)), goarch.PtrSize, &oneptrmask[0], gcw, &state)
 	}
 
+	// Scan conservatively the extended register state.
+	if gp.asyncSafePoint {
+		xRegScan(gp, gcw, &state)
+	}
+
 	// Scan the stack. Accumulate a list of stack objects.
 	var u unwinder
 	for u.init(gp, 0); u.valid(); u.next() {
diff --git a/src/runtime/preempt_noxreg.go b/src/runtime/preempt_noxreg.go
index 977bf0bcec..ee6f879779 100644
--- a/src/runtime/preempt_noxreg.go
+++ b/src/runtime/preempt_noxreg.go
@@ -25,3 +25,5 @@ func xRegSave(gp *g) {}
 func xRegRestore(gp *g) {}
 
 func (*xRegPerP) free() {}
+
+func xRegScan(gp *g, gcw *gcWork, state *stackScanState) {}
diff --git a/src/runtime/preempt_xreg.go b/src/runtime/preempt_xreg.go
index cc52c5f3c4..8e7c13338c 100644
--- a/src/runtime/preempt_xreg.go
+++ b/src/runtime/preempt_xreg.go
@@ -10,8 +10,8 @@
 // While asynchronous preemption stores general-purpose (GP) registers on the
 // preempted goroutine's own stack, extended register state can be used to save
 // non-GP state off the stack. In particular, this is meant for large vector
-// register files. Currently, we assume this contains only scalar data, though
-// we could change this constraint by conservatively scanning this memory.
+// register files. This memory is conservatively scanned to enable using
+// non-GP registers for operations that may involve pointers.
 //
 // For an architecture to support extended register state, it must provide a Go
 // definition of an xRegState type for storing the state, and its asyncPreempt
@@ -20,6 +20,7 @@
 package runtime
 
 import (
+	"internal/abi"
 	"internal/runtime/sys"
 	"unsafe"
 )
@@ -135,3 +136,29 @@ func (xRegs *xRegPerP) free() {
 		unlock(&xRegAlloc.lock)
 	}
 }
+
+// xRegScan conservatively scans the extended register state.
+//
+// This is supposed to be called only by scanstack when it handles async preemption.
+func xRegScan(gp *g, gcw *gcWork, state *stackScanState) {
+	// Regular async preemption always provides the extended register state.
+	if gp.xRegs.state == nil {
+		var u unwinder
+		for u.init(gp, 0); u.valid(); u.next() {
+			if u.frame.fn.valid() && u.frame.fn.funcID == abi.FuncID_debugCallV2 {
+				return
+			}
+		}
+		println("runtime: gp=", gp, ", goid=", gp.goid)
+		throw("gp.xRegs.state == nil on a scanstack attempt during async preemption")
+	}
+	b := uintptr(unsafe.Pointer(&gp.xRegs.state.regs))
+	n := uintptr(unsafe.Sizeof(gp.xRegs.state.regs))
+	if debugScanConservative {
+		print("begin scan xRegs of goroutine ", gp.goid, " at [", hex(b), ",", hex(b+n), ")\n")
+	}
+	scanConservative(b, n, nil, gcw, state)
+	if debugScanConservative {
+		print("end scan xRegs of goroutine ", gp.goid, "\n")
+	}
+}