pkg/proc: use constants to describe variable value

_fixtures/consts.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+	"fmt"
+	"runtime"
+)
+
+type ConstType uint8
+
+const (
+	constZero ConstType = iota
+	constOne
+	constTwo
+	constThree
+)
+
+type BitFieldType uint8
+
+const (
+	bitZero BitFieldType = 1 << iota
+	bitOne
+	bitTwo
+	bitThree
+	bitFour
+)
+
+func main() {
+	a := constTwo
+	b := constThree
+	c := bitZero | bitOne
+	d := BitFieldType(33)
+	e := ConstType(10)
+	f := BitFieldType(0)
+	runtime.Breakpoint()
+	fmt.Println(a, b, c, d, e, f)
+}

pkg/proc/bininfo.go

@@ -53,6 +53,9 @@ type BinaryInfo struct {
 	moduleData         []moduleData
 	nameOfRuntimeType  map[uintptr]nameOfRuntimeTypeEntry
 
+	// consts[off] lists all the constants with the type defined at offset off.
+	consts constantsMap
+
 	loadErrMu sync.Mutex
 	loadErr   error
 }
@@ -83,13 +86,17 @@ type Function struct {
 // or the empty string if there is none.
 // Borrowed from $GOROOT/debug/gosym/symtab.go
 func (fn *Function) PackageName() string {
-	pathend := strings.LastIndex(fn.Name, "/")
+	return packageName(fn.Name)
+}
+
+func packageName(name string) string {
+	pathend := strings.LastIndex(name, "/")
 	if pathend < 0 {
 		pathend = 0
 	}
 
-	if i := strings.Index(fn.Name[pathend:], "."); i != -1 {
-		return fn.Name[:pathend+i]
+	if i := strings.Index(name[pathend:], "."); i != -1 {
+		return name[:pathend+i]
 	}
 	return ""
 }
@@ -119,6 +126,20 @@ func (fn *Function) BaseName() string {
 	return fn.Name
 }
 
+type constantsMap map[dwarf.Offset]*constantType
+
+type constantType struct {
+	initialized bool
+	values      []constantValue
+}
+
+type constantValue struct {
+	name      string
+	fullName  string
+	value     int64
+	singleBit bool
+}
+
 type loclistReader struct {
 	data  []byte
 	cur   int

pkg/proc/eval.go

@@ -184,7 +184,7 @@ func (scope *EvalScope) evalAST(t ast.Expr) (*Variable, error) {
 				return scope.Gvar.clone(), nil
 			} else if maybePkg.Name == "runtime" && node.Sel.Name == "frameoff" {
 				return newConstant(constant.MakeInt64(scope.frameOffset), scope.Mem), nil
-			} else if v, err := scope.packageVarAddr(maybePkg.Name + "." + node.Sel.Name); err == nil {
+			} else if v, err := scope.findGlobal(maybePkg.Name + "." + node.Sel.Name); err == nil {
 				return v, nil
 			}
 		}
@@ -586,7 +586,7 @@ func (scope *EvalScope) evalIdent(node *ast.Ident) (*Variable, error) {
 	// if it's not a local variable then it could be a package variable w/o explicit package name
 	_, _, fn := scope.BinInfo.PCToLine(scope.PC)
 	if fn != nil {
-		if v, err := scope.packageVarAddr(fn.PackageName() + "." + node.Name); err == nil {
+		if v, err := scope.findGlobal(fn.PackageName() + "." + node.Name); err == nil {
 			v.Name = node.Name
 			return v, nil
 		}

pkg/proc/moduledata.go

@@ -17,7 +17,7 @@ func loadModuleData(bi *BinaryInfo, mem MemoryReadWriter) (err error) {
 	bi.loadModuleDataOnce.Do(func() {
 		scope := &EvalScope{0, op.DwarfRegisters{}, mem, nil, bi, 0}
 		var md *Variable
-		md, err = scope.packageVarAddr("runtime.firstmoduledata")
+		md, err = scope.findGlobal("runtime.firstmoduledata")
 		if err != nil {
 			return
 		}
@@ -122,7 +122,7 @@ func resolveNameOff(bi *BinaryInfo, typeAddr uintptr, off uintptr, mem MemoryRea
 
 func reflectOffsMapAccess(bi *BinaryInfo, off uintptr, mem MemoryReadWriter) (*Variable, error) {
 	scope := &EvalScope{0, op.DwarfRegisters{}, mem, nil, bi, 0}
-	reflectOffs, err := scope.packageVarAddr("runtime.reflectOffs")
+	reflectOffs, err := scope.findGlobal("runtime.reflectOffs")
 	if err != nil {
 		return nil, err
 	}

pkg/proc/types.go

@@ -177,6 +177,7 @@ func (bi *BinaryInfo) loadDebugInfoMaps(debugLineBytes []byte, wg *sync.WaitGrou
 	bi.packageVars = make(map[string]dwarf.Offset)
 	bi.Functions = []Function{}
 	bi.compileUnits = []*compileUnit{}
+	bi.consts = make(map[dwarf.Offset]*constantType)
 	reader := bi.DwarfReader()
 	var cu *compileUnit = nil
 	for entry, err := reader.Next(); entry != nil; entry, err = reader.Next() {
@@ -224,6 +225,22 @@ func (bi *BinaryInfo) loadDebugInfoMaps(debugLineBytes []byte, wg *sync.WaitGrou
 				bi.packageVars[n] = entry.Offset
 			}
 
+		case dwarf.TagConstant:
+			name, okName := entry.Val(dwarf.AttrName).(string)
+			typ, okType := entry.Val(dwarf.AttrType).(dwarf.Offset)
+			val, okVal := entry.Val(dwarf.AttrConstValue).(int64)
+			if okName && okType && okVal {
+				if !cu.isgo {
+					name = "C." + name
+				}
+				ct := bi.consts[typ]
+				if ct == nil {
+					ct = &constantType{}
+					bi.consts[typ] = ct
+				}
+				ct.values = append(ct.values, constantValue{name: name, fullName: name, value: val})
+			}
+
 		case dwarf.TagSubprogram:
 			ok1 := false
 			var lowpc, highpc uint64

pkg/proc/variables.go

@@ -54,6 +54,8 @@ const (
 	// VariableShadowed is set for local variables that are shadowed by a
 	// variable with the same name in another scope
 	VariableShadowed
+	// VariableConstant means this variable is a constant value
+	VariableConstant
 )
 
 // Variable represents a variable. It contains the address, name,
@@ -291,6 +293,7 @@ func newConstant(val constant.Value, mem MemoryReadWriter) *Variable {
 		v.Kind = reflect.String
 		v.Len = int64(len(constant.StringVal(val)))
 	}
+	v.Flags |= VariableConstant
 	return v
 }
 
@@ -642,7 +645,7 @@ func (scope *EvalScope) PackageVariables(cfg LoadConfig) ([]*Variable, error) {
 	return vars, nil
 }
 
-func (scope *EvalScope) packageVarAddr(name string) (*Variable, error) {
+func (scope *EvalScope) findGlobal(name string) (*Variable, error) {
 	for n, off := range scope.BinInfo.packageVars {
 		if n == name || strings.HasSuffix(n, "/"+name) {
 			reader := scope.DwarfReader()
@@ -654,6 +657,28 @@ func (scope *EvalScope) packageVarAddr(name string) (*Variable, error) {
 			return scope.extractVarInfoFromEntry(entry)
 		}
 	}
+	for offset, ctyp := range scope.BinInfo.consts {
+		for _, cval := range ctyp.values {
+			if cval.fullName == name {
+				t, err := scope.Type(offset)
+				if err != nil {
+					return nil, err
+				}
+				v := scope.newVariable(name, 0x0, t, scope.Mem)
+				switch v.Kind {
+				case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+					v.Value = constant.MakeInt64(cval.value)
+				case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+					v.Value = constant.MakeUint64(uint64(cval.value))
+				default:
+					return nil, fmt.Errorf("unsupported constant kind %v", v.Kind)
+				}
+				v.Flags |= VariableConstant
+				v.loaded = true
+				return v, nil
+			}
+		}
+	}
 	return nil, fmt.Errorf("could not find symbol value for %s", name)
 }
 
@@ -1724,6 +1749,100 @@ func (v *Variable) loadInterface(recurseLevel int, loadData bool, cfg LoadConfig
 	}
 }
 
+// ConstDescr describes the value of v using constants.
+func (v *Variable) ConstDescr() string {
+	if v.bi == nil || (v.Flags&VariableConstant != 0) {
+		return ""
+	}
+	ctyp := v.bi.consts.Get(v.DwarfType)
+	if ctyp == nil {
+		return ""
+	}
+	if typename := v.DwarfType.Common().Name; strings.Index(typename, ".") < 0 || strings.HasPrefix(typename, "C.") {
+		// only attempt to use constants for user defined type, otherwise every
+		// int variable with value 1 will be described with os.SEEK_CUR and other
+		// similar problems.
+		return ""
+	}
+
+	switch v.Kind {
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		fallthrough
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		n, _ := constant.Int64Val(v.Value)
+		return ctyp.describe(n)
+	}
+	return ""
+}
+
+// popcnt is the number of bits set to 1 in x.
+// It's the same as math/bits.OnesCount64, copied here so that we can build
+// on versions of go that don't have math/bits.
+func popcnt(x uint64) int {
+	const m0 = 0x5555555555555555 // 01010101 ...
+	const m1 = 0x3333333333333333 // 00110011 ...
+	const m2 = 0x0f0f0f0f0f0f0f0f // 00001111 ...
+	const m = 1<<64 - 1
+	x = x>>1&(m0&m) + x&(m0&m)
+	x = x>>2&(m1&m) + x&(m1&m)
+	x = (x>>4 + x) & (m2 & m)
+	x += x >> 8
+	x += x >> 16
+	x += x >> 32
+	return int(x) & (1<<7 - 1)
+}
+
+func (cm constantsMap) Get(typ godwarf.Type) *constantType {
+	ctyp := cm[typ.Common().Offset]
+	if ctyp == nil {
+		return nil
+	}
+	typepkg := packageName(typ.String()) + "."
+	if !ctyp.initialized {
+		ctyp.initialized = true
+		sort.Sort(constantValuesByValue(ctyp.values))
+		for i := range ctyp.values {
+			if strings.HasPrefix(ctyp.values[i].name, typepkg) {
+				ctyp.values[i].name = ctyp.values[i].name[len(typepkg):]
+			}
+			if popcnt(uint64(ctyp.values[i].value)) == 1 {
+				ctyp.values[i].singleBit = true
+			}
+		}
+	}
+	return ctyp
+}
+
+func (ctyp *constantType) describe(n int64) string {
+	for _, val := range ctyp.values {
+		if val.value == n {
+			return val.name
+		}
+	}
+
+	if n == 0 {
+		return ""
+	}
+
+	// If all the values for this constant only have one bit set we try to
+	// represent the value as a bitwise or of constants.
+
+	fields := []string{}
+	for _, val := range ctyp.values {
+		if !val.singleBit {
+			continue
+		}
+		if n&val.value != 0 {
+			fields = append(fields, val.name)
+			n = n & ^val.value
+		}
+	}
+	if n == 0 {
+		return strings.Join(fields, "|")
+	}
+	return ""
+}
+
 type variablesByDepth struct {
 	vars   []*Variable
 	depths []int
@@ -1833,3 +1952,9 @@ func (scope *EvalScope) variablesByTag(tag dwarf.Tag, cfg *LoadConfig) ([]*Varia
 
 	return vars, nil
 }
+
+type constantValuesByValue []constantValue
+
+func (v constantValuesByValue) Len() int               { return len(v) }
+func (v constantValuesByValue) Less(i int, j int) bool { return v[i].value < v[j].value }
+func (v constantValuesByValue) Swap(i int, j int)      { v[i], v[j] = v[j], v[i] }

service/api/conversions.go

@@ -139,7 +139,10 @@ func ConvertVar(v *proc.Variable) *Variable {
 		case reflect.String, reflect.Func:
 			r.Value = constant.StringVal(v.Value)
 		default:
-			r.Value = v.Value.String()
+			r.Value = v.ConstDescr()
+			if r.Value == "" {
+				r.Value = v.Value.String()
+			}
 		}
 	}
 

service/api/types.go

@@ -165,6 +165,9 @@ const (
 	// VariableShadowed is set for local variables that are shadowed by a
 	// variable with the same name in another scope
 	VariableShadowed = VariableFlags(proc.VariableShadowed)
+
+	// VariableConstant means this variable is a constant value
+	VariableConstant
 )
 
 // Variable describes a variable.

service/test/variables_test.go

@@ -949,3 +949,30 @@ func TestPackageRenames(t *testing.T) {
 		}
 	})
 }
+
+func TestConstants(t *testing.T) {
+	testcases := []varTest{
+		{"a", true, "constTwo", "", "main.ConstType", nil},
+		{"b", true, "constThree", "", "main.ConstType", nil},
+		{"c", true, "bitZero|bitOne", "", "main.BitFieldType", nil},
+		{"d", true, "33", "", "main.BitFieldType", nil},
+		{"e", true, "10", "", "main.ConstType", nil},
+		{"f", true, "0", "", "main.BitFieldType", nil},
+		{"bitZero", true, "1", "", "main.BitFieldType", nil},
+		{"bitOne", true, "2", "", "main.BitFieldType", nil},
+		{"constTwo", true, "2", "", "main.ConstType", nil},
+	}
+	ver, _ := goversion.Parse(runtime.Version())
+	if ver.Major > 0 && !ver.AfterOrEqual(goversion.GoVersion{1, 10, -1, 0, 0, ""}) {
+		// Not supported on 1.9 or earlier
+		return
+	}
+	withTestProcess("consts", t, func(p proc.Process, fixture protest.Fixture) {
+		assertNoError(proc.Continue(p), t, "Continue")
+		for _, testcase := range testcases {
+			variable, err := evalVariable(p, testcase.name, pnormalLoadConfig)
+			assertNoError(err, t, fmt.Sprintf("EvalVariable(%s)", testcase.name))
+			assertVariable(t, variable, testcase)
+		}
+	})
+}