proc: fix stacktraces on freebsd/amd64/go1.20 (#3458)

TestStacktraceGoroutine failed intermittently on freebsd/amd64/go1.20.

This happens because of two windows, in the scheduler (right after
parking a goroutine and just before resuming a parked goroutine) where
a thread is associated with a goroutine but running in the system stack
and there is no systemstack_switch frame to connect the two stacks.

pkg/proc/amd64_arch.go

@@ -200,11 +200,19 @@ func amd64SwitchStack(it *stackIterator, _ *op.DwarfRegisters) bool {
 
 		return true
 
-	case "runtime.goexit", "runtime.rt0_go", "runtime.mcall":
+	case "runtime.goexit", "runtime.rt0_go":
 		// Look for "top of stack" functions.
 		it.atend = true
 		return true
 
+	case "runtime.mcall":
+		if it.systemstack && it.g != nil {
+			it.switchToGoroutineStack()
+			return true
+		}
+		it.atend = true
+		return true
+
 	case "runtime.mstart":
 		// Calls to runtime.systemstack will switch to the systemstack then:
 		// 1. alter the goroutine stack so that it looks like systemstack_switch

pkg/proc/arm64_arch.go

@@ -217,10 +217,19 @@ func arm64SwitchStack(it *stackIterator, callFrameRegs *op.DwarfRegisters) bool
 			return true
 		}
 
-	case "runtime.goexit", "runtime.rt0_go", "runtime.mcall":
+	case "runtime.goexit", "runtime.rt0_go":
 		// Look for "top of stack" functions.
 		it.atend = true
 		return true
+
+	case "runtime.mcall":
+		if it.systemstack && it.g != nil {
+			it.switchToGoroutineStack()
+			return true
+		}
+		it.atend = true
+		return true
+
 	case "crosscall2":
 		// The offsets get from runtime/cgo/asm_arm64.s:10
 		bpoff := uint64(14)

pkg/proc/i386_arch.go

@@ -127,11 +127,19 @@ func i386SwitchStack(it *stackIterator, _ *op.DwarfRegisters) bool {
 	switch it.frame.Current.Fn.Name {
 	case "runtime.asmcgocall", "runtime.cgocallback_gofunc": // TODO(chainhelen), need to support cgo stacktraces.
 		return false
-	case "runtime.goexit", "runtime.rt0_go", "runtime.mcall":
+	case "runtime.goexit", "runtime.rt0_go":
 		// Look for "top of stack" functions.
 		it.atend = true
 		return true
 
+	case "runtime.mcall":
+		if it.systemstack && it.g != nil {
+			it.switchToGoroutineStack()
+			return true
+		}
+		it.atend = true
+		return true
+
 	case "runtime.mstart":
 		// Calls to runtime.systemstack will switch to the systemstack then:
 		// 1. alter the goroutine stack so that it looks like systemstack_switch

pkg/proc/ppc64le_arch.go

@@ -106,10 +106,17 @@ func ppc64leSwitchStack(it *stackIterator, callFrameRegs *op.DwarfRegisters) boo
 		switch it.frame.Current.Fn.Name {
 		case "runtime.asmcgocall", "runtime.cgocallback_gofunc", "runtime.sigpanic", "runtime.cgocallback":
 			//do nothing
-		case "runtime.goexit", "runtime.rt0_go", "runtime.mcall":
+		case "runtime.goexit", "runtime.rt0_go":
 			// Look for "top of stack" functions.
 			it.atend = true
 			return true
+		case "runtime.mcall":
+			if it.systemstack && it.g != nil {
+				it.switchToGoroutineStack()
+				return true
+			}
+			it.atend = true
+			return true
 		case "crosscall2":
 			//The offsets get from runtime/cgo/asm_ppc64x.s:10
 			newsp, _ := readUintRaw(it.mem, it.regs.SP()+8*24, int64(it.bi.Arch.PtrSize()))