Read string type from memory

proctl/proctl_linux_amd64.go

@@ -12,6 +12,7 @@ import (
 	"os"
 	"strconv"
 	"syscall"
+	"unsafe"
 
 	"github.com/derekparker/dbg/dwarf/frame"
 	"github.com/derekparker/dbg/dwarf/line"
@@ -376,6 +377,8 @@ func (dbp *DebuggedProcess) extractValue(instructions []byte, typ interface{}) (
 	offset := uintptr(int64(regs.Rsp) + off)
 
 	switch typ.(type) {
+	case *dwarf.StructType:
+		return dbp.readString(offset)
 	case *dwarf.IntType:
 		return dbp.readInt(offset)
 	case *dwarf.FloatType:
@@ -385,6 +388,25 @@ func (dbp *DebuggedProcess) extractValue(instructions []byte, typ interface{}) (
 	return "", fmt.Errorf("could not find value for type %s", typ)
 }
 
+func (dbp *DebuggedProcess) readString(addr uintptr) (string, error) {
+	val, err := dbp.readMemory(addr, 8)
+	if err != nil {
+		return "", err
+	}
+
+	// deref the pointer to the string
+	addr = uintptr(binary.LittleEndian.Uint64(val))
+	val, err = dbp.readMemory(addr, 16)
+	if err != nil {
+		return "", err
+	}
+
+	i := bytes.IndexByte(val, 0x0)
+	val = val[:i]
+	str := *(*string)(unsafe.Pointer(&val))
+	return str, nil
+}
+
 func (dbp *DebuggedProcess) readInt(addr uintptr) (string, error) {
 	val, err := dbp.readMemory(addr, 8)
 	if err != nil {

proctl/proctl_test.go

@@ -231,6 +231,7 @@ func TestVariableEvaluation(t *testing.T) {
 		value   string
 		varType string
 	}{
+		{"a1", "foo", "struct string"},
 		{"a2", "6", "int"},
 		{"a3", "7.23", "float64"},
 	}
@@ -257,7 +258,7 @@ func TestVariableEvaluation(t *testing.T) {
 			}
 
 			if variable.Value != tc.value {
-				t.Fatalf("Expected %s got %s\n", tc.value, variable.Value)
+				t.Fatalf("Expected %#v got %#v\n", tc.value, variable.Value)
 			}
 		}
 	})