diff --git a/src/runtime/os3_plan9.go b/src/runtime/os3_plan9.go
index 0b313d75e3..b05965b63d 100644
--- a/src/runtime/os3_plan9.go
+++ b/src/runtime/os3_plan9.go
@@ -121,7 +121,7 @@ func sighandler(_ureg *ureg, note *byte, gp *g) int {
 Throw:
 	_g_.m.throwing = 1
 	_g_.m.caughtsig.set(gp)
-	startpanic()
+	startpanic_m()
 	print(notestr, "\n")
 	print("PC=", hex(c.pc()), "\n")
 	print("\n")
diff --git a/src/runtime/panic.go b/src/runtime/panic.go
index 715e802d10..cd2b18cc51 100644
--- a/src/runtime/panic.go
+++ b/src/runtime/panic.go
@@ -542,15 +542,9 @@ func gopanic(e interface{}) {
 	// the world, we call preprintpanics to invoke all necessary Error
 	// and String methods to prepare the panic strings before startpanic.
 	preprintpanics(gp._panic)
-	startpanic()
 
-	// startpanic set panicking, which will block main from exiting,
-	// so now OK to decrement runningPanicDefers.
-	atomic.Xadd(&runningPanicDefers, -1)
-
-	printpanics(gp._panic)
-	dopanic(0)       // should not return
-	*(*int)(nil) = 0 // not reached
+	fatalpanic(gp._panic) // should not return
+	*(*int)(nil) = 0      // not reached
 }
 
 // getargp returns the location where the caller
@@ -585,22 +579,6 @@ func gorecover(argp uintptr) interface{} {
 	return nil
 }
 
-//go:nosplit
-func startpanic() {
-	systemstack(startpanic_m)
-}
-
-//go:nosplit
-func dopanic(unused int) {
-	pc := getcallerpc()
-	sp := getcallersp(unsafe.Pointer(&unused))
-	gp := getg()
-	systemstack(func() {
-		dopanic_m(gp, pc, sp) // should never return
-	})
-	*(*int)(nil) = 0
-}
-
 //go:linkname sync_throw sync.throw
 func sync_throw(s string) {
 	throw(s)
@@ -613,8 +591,7 @@ func throw(s string) {
 	if gp.m.throwing == 0 {
 		gp.m.throwing = 1
 	}
-	startpanic()
-	dopanic(0)
+	fatalpanic(nil)
 	*(*int)(nil) = 0 // not reached
 }
 
@@ -655,13 +632,48 @@ func recovery(gp *g) {
 	gogo(&gp.sched)
 }
 
+// fatalpanic implements an unrecoverable panic. It freezes the
+// system, prints panic messages if msgs != nil, prints stack traces
+// starting from its caller, and terminates the process.
+//
+// If msgs != nil, it also decrements runningPanicDefers once main is
+// blocked from exiting.
+//
+//go:nosplit
+func fatalpanic(msgs *_panic) {
+	pc := getcallerpc()
+	sp := getcallersp(unsafe.Pointer(&msgs))
+	gp := getg()
+	// Switch to the system stack to avoid any stack growth, which
+	// may make things worse if the runtime is in a bad state.
+	systemstack(func() {
+		if startpanic_m() && msgs != nil {
+			// There were panic messages and startpanic_m
+			// says it's okay to try to print them.
+
+			// startpanic_m set panicking, which will
+			// block main from exiting, so now OK to
+			// decrement runningPanicDefers.
+			atomic.Xadd(&runningPanicDefers, -1)
+
+			printpanics(msgs)
+		}
+
+		dopanic_m(gp, pc, sp) // should never return
+	})
+	*(*int)(nil) = 0 // not reached
+}
+
 // startpanic_m prepares for an unrecoverable panic.
 //
+// It returns true if panic messages should be printed, or false if
+// the runtime is in bad shape and should just print stacks.
+//
 // It can have write barriers because the write barrier explicitly
 // ignores writes once dying > 0.
 //
 //go:yeswritebarrierrec
-func startpanic_m() {
+func startpanic_m() bool {
 	_g_ := getg()
 	if mheap_.cachealloc.size == 0 { // very early
 		print("runtime: panic before malloc heap initialized\n")
@@ -682,15 +694,13 @@ func startpanic_m() {
 			schedtrace(true)
 		}
 		freezetheworld()
-		return
+		return true
 	case 1:
-		// Something failed while panicking, probably the print of the
-		// argument to panic().  Just print a stack trace and exit.
+		// Something failed while panicking.
+		// Just print a stack trace and exit.
 		_g_.m.dying = 2
 		print("panic during panic\n")
-		dopanic(0)
-		exit(3)
-		fallthrough
+		return false
 	case 2:
 		// This is a genuine bug in the runtime, we couldn't even
 		// print the stack trace successfully.
@@ -701,6 +711,7 @@ func startpanic_m() {
 	default:
 		// Can't even print! Just exit.
 		exit(5)
+		return false // Need to return something.
 	}
 }
 
diff --git a/src/runtime/signal_sighandler.go b/src/runtime/signal_sighandler.go
index bf2237c981..13448929bc 100644
--- a/src/runtime/signal_sighandler.go
+++ b/src/runtime/signal_sighandler.go
@@ -83,7 +83,7 @@ func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	_g_.m.caughtsig.set(gp)
 
 	if crashing == 0 {
-		startpanic()
+		startpanic_m()
 	}
 
 	if sig < uint32(len(sigtable)) {