proc: make nested function calls work when stopped at a sw breakpoint (#2232)

evalFunctionCall needs to remove the breakpoint from the current thread
after starting the function call injection, otherwise Continue will
think that the thread is stopped at a breakpoint and return to the user
instead of continuing the call injection.

_fixtures/fncall.go

@@ -193,7 +193,7 @@ func main() {
 
 	d := &Derived{3, Base{4}}
 
-	runtime.Breakpoint()
+	runtime.Breakpoint() // breakpoint here
 	call1(one, two)
 	fn2clos(2)
 	strings.LastIndexByte(stringslice[1], 'w')

pkg/proc/fncall.go

@@ -316,6 +316,7 @@ func evalFunctionCall(scope *EvalScope, node *ast.CallExpr) (*Variable, error) {
 
 	fncallLog("function call initiated %v frame size %d goroutine %d (thread %d)", fncall.fn, fncall.argFrameSize, scope.g.ID, thread.ThreadID())
 
+	thread.Breakpoint().Clear() // since we moved address in PC the thread is no longer stopped at a breakpoint, leaving the breakpoint set will confuse Continue
 	p.fncallForG[scope.g.ID].startThreadID = thread.ThreadID()
 
 	spoff := int64(scope.Regs.Uint64Val(scope.Regs.SPRegNum)) - int64(scope.g.stack.hi)
@@ -946,6 +947,10 @@ func isCallInjectionStop(t *Target, thread Thread, loc *Location) bool {
 	if !strings.HasPrefix(loc.Fn.Name, debugCallFunctionNamePrefix1) && !strings.HasPrefix(loc.Fn.Name, debugCallFunctionNamePrefix2) {
 		return false
 	}
+	if loc.PC == loc.Fn.Entry {
+		// call injection just started, did not make any progress before being interrupted by a concurrent breakpoint.
+		return false
+	}
 	text, err := disassembleCurrentInstruction(t, thread, -1)
 	if err != nil || len(text) <= 0 {
 		return false

service/test/variables_test.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"go/constant"
+	"io/ioutil"
 	"path/filepath"
 	"runtime"
 	"sort"
@@ -1269,6 +1270,9 @@ func TestCallFunction(t *testing.T) {
 		if err != nil {
 			t.Skip("function calls not supported on this version of go")
 		}
+
+		testCallFunctionSetBreakpoint(t, p, fixture)
+
 		assertNoError(p.Continue(), t, "Continue()")
 		for _, tc := range testcases {
 			testCallFunction(t, p, tc)
@@ -1302,6 +1306,17 @@ func TestCallFunction(t *testing.T) {
 	})
 }
 
+func testCallFunctionSetBreakpoint(t *testing.T, p *proc.Target, fixture protest.Fixture) {
+	buf, err := ioutil.ReadFile(fixture.Source)
+	assertNoError(err, t, "ReadFile")
+	for i, line := range strings.Split(string(buf), "\n") {
+		if strings.Contains(line, "// breakpoint here") {
+			setFileBreakpoint(p, t, fixture, i+1)
+			return
+		}
+	}
+}
+
 func testCallFunction(t *testing.T, p *proc.Target, tc testCaseCallFunction) {
 	const unsafePrefix = "-unsafe "