fix StepInstruction on 1 byte instruction with a software breackpoint (#3084)

_fixtures/break/break_amd64.s

@@ -0,0 +1,5 @@
+#include "textflag.h"
+
+TEXT ·asmBrk(SB),0,$0-0
+	BYTE	$0xcc
+	RET

_fixtures/break/main.go

@@ -0,0 +1,7 @@
+package main
+
+func asmBrk()
+
+func main() {
+	asmBrk()
+}

pkg/proc/proc_test.go

@@ -2691,6 +2691,26 @@ func TestStepOutDeferReturnAndDirectCall(t *testing.T) {
 		{contStepout, 28}})
 }
 
+func TestStepInstructionOnBreakpoint(t *testing.T) {
+	if runtime.GOARCH != "amd64" {
+		t.Skipf("skipping since not amd64")
+	}
+	// StepInstruction should step one instruction forward when
+	// PC is on a 1 byte instruction with a software breakpoint.
+	protest.AllowRecording(t)
+	withTestProcess("break/", t, func(p *proc.Target, fixture protest.Fixture) {
+		setFileBreakpoint(p, t, filepath.ToSlash(filepath.Join(fixture.BuildDir, "break_amd64.s")), 4)
+
+		assertNoError(p.Continue(), t, "Continue()")
+
+		pc := getRegisters(p, t).PC()
+		assertNoError(p.StepInstruction(), t, "StepInstruction()")
+		if pc == getRegisters(p, t).PC() {
+			t.Fatal("Could not step a single instruction")
+		}
+	})
+}
+
 func TestStepOnCallPtrInstr(t *testing.T) {
 	protest.AllowRecording(t)
 	withTestProcess("teststepprog", t, func(p *proc.Target, fixture protest.Fixture) {

pkg/proc/target_exec.go

@@ -433,7 +433,7 @@ func (grp *TargetGroup) StepInstruction() (err error) {
 		return err
 	}
 	thread.Breakpoint().Clear()
-	err = thread.SetCurrentBreakpoint(true)
+	err = thread.SetCurrentBreakpoint(false)
 	if err != nil {
 		return err
 	}