proc: do not check return args when loading return vals of call injection

When the function we are calling is an autogenerated stub (because, for
example, we are calling it through a function pointer) the declaration
line of variables is meaningless and could cause us to discard valid
return arguments.

pkg/dwarf/reader/variables.go

@@ -23,6 +23,7 @@ const (
 	VariablesOnlyVisible VariablesFlags = 1 << iota
 	VariablesSkipInlinedSubroutines
 	VariablesTrustDeclLine
+	VariablesNoDeclLineCheck
 )
 
 // Variables returns a list of variables contained inside 'root'.
@@ -60,7 +61,7 @@ func variablesInternal(v []Variable, root *godwarf.Tree, depth int, pc uint64, l
 			// are defined.
 			o = 1
 		}
-		if declLine, ok := root.Val(dwarf.AttrDeclLine).(int64); !ok || line >= int(declLine)+o {
+		if declLine, ok := root.Val(dwarf.AttrDeclLine).(int64); (flags&VariablesNoDeclLineCheck != 0) || !ok || line >= int(declLine)+o {
 			return append(v, Variable{root, depth})
 		}
 		return v

pkg/proc/breakpoints.go

@@ -899,7 +899,7 @@ func (rbpi *returnBreakpointInfo) Collect(t *Target, thread Thread) []*Variable
 		return returnInfoError("could not read function entry", err, thread.ProcessMemory())
 	}
 
-	vars, err := scope.Locals()
+	vars, err := scope.Locals(0)
 	if err != nil {
 		return returnInfoError("could not evaluate return variables", err, thread.ProcessMemory())
 	}

pkg/proc/eval.go

@@ -49,13 +49,21 @@ type EvalScope struct {
 	// The goroutine executing the expression evaluation shall signal that the
 	// evaluation is complete by closing the continueRequest channel.
 	callCtx *callContext
-
-	// If trustArgOrder is true function arguments that don't have an address
-	// will have one assigned by looking at their position in the argument
-	// list.
-	trustArgOrder bool
 }
 
+type localsFlags uint8
+
+const (
+	// If localsTrustArgOrder is set function arguments that don't have an
+	// address will have one assigned by looking at their position in the argument
+	// list.
+	localsTrustArgOrder localsFlags = 1 << iota
+
+	// If localsNoDeclLineCheck the declaration line isn't checked at
+	// all to determine if the variable is in scope.
+	localsNoDeclLineCheck
+)
+
 // ConvertEvalScope returns a new EvalScope in the context of the
 // specified goroutine ID and stack frame.
 // If deferCall is > 0 the eval scope will be relative to the specified deferred call.
@@ -201,12 +209,12 @@ func isAssignment(err error) (int, bool) {
 }
 
 // Locals returns all variables in 'scope'.
-func (scope *EvalScope) Locals() ([]*Variable, error) {
+func (scope *EvalScope) Locals(flags localsFlags) ([]*Variable, error) {
 	if scope.Fn == nil {
 		return nil, errors.New("unable to find function context")
 	}
 
-	trustArgOrder := scope.trustArgOrder && scope.BinInfo.Producer() != "" && goversion.ProducerAfterOrEqual(scope.BinInfo.Producer(), 1, 12) && scope.Fn != nil && (scope.PC == scope.Fn.Entry)
+	trustArgOrder := (flags&localsTrustArgOrder != 0) && scope.BinInfo.Producer() != "" && goversion.ProducerAfterOrEqual(scope.BinInfo.Producer(), 1, 12) && scope.Fn != nil && (scope.PC == scope.Fn.Entry)
 
 	dwarfTree, err := scope.image().getDwarfTree(scope.Fn.offset)
 	if err != nil {
@@ -214,6 +222,9 @@ func (scope *EvalScope) Locals() ([]*Variable, error) {
 	}
 
 	variablesFlags := reader.VariablesOnlyVisible
+	if flags&localsNoDeclLineCheck != 0 {
+		variablesFlags = reader.VariablesNoDeclLineCheck
+	}
 	if scope.BinInfo.Producer() != "" && goversion.ProducerAfterOrEqual(scope.BinInfo.Producer(), 1, 15) {
 		variablesFlags |= reader.VariablesTrustDeclLine
 	}
@@ -417,7 +428,7 @@ func (scope *EvalScope) SetVariable(name, value string) error {
 
 // LocalVariables returns all local variables from the current function scope.
 func (scope *EvalScope) LocalVariables(cfg LoadConfig) ([]*Variable, error) {
-	vars, err := scope.Locals()
+	vars, err := scope.Locals(0)
 	if err != nil {
 		return nil, err
 	}
@@ -431,7 +442,7 @@ func (scope *EvalScope) LocalVariables(cfg LoadConfig) ([]*Variable, error) {
 
 // FunctionArguments returns the name, value, and type of all current function arguments.
 func (scope *EvalScope) FunctionArguments(cfg LoadConfig) ([]*Variable, error) {
-	vars, err := scope.Locals()
+	vars, err := scope.Locals(0)
 	if err != nil {
 		return nil, err
 	}
@@ -1134,7 +1145,7 @@ func (scope *EvalScope) evalIdent(node *ast.Ident) (*Variable, error) {
 		return nilVariable, nil
 	}
 
-	vars, err := scope.Locals()
+	vars, err := scope.Locals(0)
 	if err != nil {
 		return nil, err
 	}

pkg/proc/fncall.go

@@ -883,9 +883,13 @@ func funcCallStep(callScope *EvalScope, fncall *functionCallState, thread Thread
 
 		// pretend we are still inside the function we called
 		fakeFunctionEntryScope(retScope, fncall.fn, int64(regs.SP()), regs.SP()-uint64(bi.Arch.PtrSize()))
-		retScope.trustArgOrder = !bi.regabi
+		var flags localsFlags
+		flags |= localsNoDeclLineCheck // if the function we are calling is an autogenerated stub then declaration lines have no meaning
+		if !bi.regabi {
+			flags |= localsTrustArgOrder
+		}
 
-		fncall.retvars, err = retScope.Locals()
+		fncall.retvars, err = retScope.Locals(flags)
 		if err != nil {
 			fncall.err = fmt.Errorf("could not get return values: %v", err)
 			break

pkg/proc/proc_test.go

@@ -3544,7 +3544,7 @@ func testDeclLineCount(t *testing.T, p *proc.Target, lineno int, tgtvars []strin
 	assertLineNumber(p, t, lineno, "Program did not continue to correct next location")
 	scope, err := proc.GoroutineScope(p, p.CurrentThread())
 	assertNoError(err, t, fmt.Sprintf("GoroutineScope (:%d)", lineno))
-	vars, err := scope.Locals()
+	vars, err := scope.Locals(0)
 	assertNoError(err, t, fmt.Sprintf("Locals (:%d)", lineno))
 	if len(vars) != len(tgtvars) {
 		t.Fatalf("wrong number of variables %d (:%d)", len(vars), lineno)