proc: added fake runtime.curg variable

proc/eval.go

@@ -54,7 +54,9 @@ func (scope *EvalScope) evalAST(t ast.Expr) (*Variable, error) {
 	case *ast.SelectorExpr: // <expression>.<identifier>
 		// try to interpret the selector as a package variable
 		if maybePkg, ok := node.X.(*ast.Ident); ok {
-			if v, err := scope.packageVarAddr(maybePkg.Name + "." + node.Sel.Name); err == nil {
+			if maybePkg.Name == "runtime" && node.Sel.Name == "curg" {
+				return scope.Thread.getGVariable()
+			} else if v, err := scope.packageVarAddr(maybePkg.Name + "." + node.Sel.Name); err == nil {
 				return v, nil
 			}
 		}

proc/proc.go

@@ -497,7 +497,11 @@ func (dbp *Process) GoroutinesInfo() ([]*G, error) {
 	allgptr := binary.LittleEndian.Uint64(faddr)
 
 	for i := uint64(0); i < allglen; i++ {
-		g, err := parseG(dbp.CurrentThread, allgptr+(i*uint64(dbp.arch.PtrSize())), true)
+		gvar, err := dbp.CurrentThread.newGVariable(uintptr(allgptr+(i*uint64(dbp.arch.PtrSize()))), true)
+		if err != nil {
+			return nil, err
+		}
+		g, err := gvar.parseG()
 		if err != nil {
 			return nil, err
 		}

proc/threads.go

@@ -1,6 +1,7 @@
 package proc
 
 import (
+	"debug/dwarf"
 	"debug/gosym"
 	"encoding/binary"
 	"fmt"
@@ -247,6 +248,48 @@ func (thread *Thread) SetPC(pc uint64) error {
 	return regs.SetPC(thread, pc)
 }
 
+func (thread *Thread) getGVariable() (*Variable, error) {
+	regs, err := thread.Registers()
+	if err != nil {
+		return nil, err
+	}
+
+	if thread.dbp.arch.GStructOffset() == 0 {
+		// GetG was called through SwitchThread / updateThreadList during initialization
+		// thread.dbp.arch isn't setup yet (it needs a CurrentThread to read global variables from)
+		return nil, fmt.Errorf("g struct offset not initialized")
+	}
+
+	gaddrbs, err := thread.readMemory(uintptr(regs.TLS()+thread.dbp.arch.GStructOffset()), thread.dbp.arch.PtrSize())
+	if err != nil {
+		return nil, err
+	}
+	gaddr := uintptr(binary.LittleEndian.Uint64(gaddrbs))
+	
+	// On Windows, the value at TLS()+GStructOffset() is a 
+	// pointer to the G struct.
+	needsDeref := runtime.GOOS == "windows"
+
+	return thread.newGVariable(gaddr, needsDeref)
+}
+
+func (thread *Thread) newGVariable(gaddr uintptr, deref bool) (*Variable, error) {
+	typ, err := thread.dbp.findType("runtime.g")
+	if err != nil {
+		return nil, err
+	}
+
+	name := ""
+
+	if deref {
+		typ = &dwarf.PtrType{dwarf.CommonType{int64(thread.dbp.arch.PtrSize()), ""}, typ}
+	} else {
+		name = "runtime.curg"
+	}
+
+	return thread.newVariable(name, gaddr, typ), nil
+}
+
 // GetG returns information on the G (goroutine) that is executing on this thread.
 //
 // The G structure for a thread is stored in thread local storage. Here we simply
@@ -262,26 +305,12 @@ func (thread *Thread) SetPC(pc uint64) error {
 // In order to get around all this craziness, we read the address of the G structure for
 // the current thread from the thread local storage area.
 func (thread *Thread) GetG() (g *G, err error) {
-	regs, err := thread.Registers()
+	gaddr, err := thread.getGVariable()
 	if err != nil {
 		return nil, err
 	}
-	if thread.dbp.arch.GStructOffset() == 0 {
-		// GetG was called through SwitchThread / updateThreadList during initialization
-		// thread.dbp.arch isn't setup yet (it needs a CurrentThread to read global variables from)
-		return nil, fmt.Errorf("g struct offset not initialized")
-	}
-	gaddrbs, err := thread.readMemory(uintptr(regs.TLS()+thread.dbp.arch.GStructOffset()), thread.dbp.arch.PtrSize())
-	if err != nil {
-		return nil, err
-	}
-	gaddr := binary.LittleEndian.Uint64(gaddrbs)
 
-	// On Windows, the value at TLS()+GStructOffset() is a 
-	// pointer to the G struct.
-	needsDeref := runtime.GOOS == "windows"
-	
-	g, err = parseG(thread, gaddr, needsDeref)
+	g, err = gaddr.parseG()
 	if err == nil {
 		g.thread = thread
 	}

proc/variables.go

@@ -143,6 +143,10 @@ func (scope *EvalScope) newVariable(name string, addr uintptr, dwarfType dwarf.T
 	return newVariable(name, addr, dwarfType, scope.Thread.dbp, scope.Thread)
 }
 
+func (t *Thread) newVariable(name string, addr uintptr, dwarfType dwarf.Type) *Variable {
+	return newVariable(name, addr, dwarfType, t.dbp, t)
+}
+
 func (v *Variable) newVariable(name string, addr uintptr, dwarfType dwarf.Type) *Variable {
 	return newVariable(name, addr, dwarfType, v.dbp, v.mem)
 }
@@ -338,32 +342,40 @@ func (ng NoGError) Error() string {
 	return fmt.Sprintf("no G executing on thread %d", ng.tid)
 }
 
-func parseG(thread *Thread, gaddr uint64, deref bool) (*G, error) {
-	initialInstructions := make([]byte, thread.dbp.arch.PtrSize()+1)
+func (gvar *Variable) parseG() (*G, error) {
+	mem := gvar.mem
+	dbp := gvar.dbp
+	gaddr := uint64(gvar.Addr)
+	_, deref := gvar.RealType.(*dwarf.PtrType)
+
+	initialInstructions := make([]byte, dbp.arch.PtrSize()+1)
 	initialInstructions[0] = op.DW_OP_addr
 	binary.LittleEndian.PutUint64(initialInstructions[1:], gaddr)
 	if deref {
-		gaddrbytes, err := thread.readMemory(uintptr(gaddr), thread.dbp.arch.PtrSize())
+		gaddrbytes, err := mem.readMemory(uintptr(gaddr), dbp.arch.PtrSize())
 		if err != nil {
 			return nil, fmt.Errorf("error derefing *G %s", err)
 		}
 		initialInstructions = append([]byte{op.DW_OP_addr}, gaddrbytes...)
 		gaddr = binary.LittleEndian.Uint64(gaddrbytes)
 		if gaddr == 0 {
-			return nil, NoGError{tid: thread.ID}
+			id := 0
+			if thread, ok := mem.(*Thread); ok {
+				id = thread.ID
+			}
+			return nil, NoGError{tid: id}
 		}
 	}
 
-	rdr := thread.dbp.DwarfReader()
+	rdr := dbp.DwarfReader()
 	rdr.Seek(0)
 	entry, err := rdr.SeekToTypeNamed("runtime.g")
 	if err != nil {
 		return nil, err
 	}
 
-	var mem memoryReadWriter = thread
-	if gtype, err := thread.dbp.dwarf.Type(entry.Offset); err == nil {
-		mem = cacheMemory(thread, uintptr(gaddr), int(gtype.Size()))
+	if gtype, err := dbp.dwarf.Type(entry.Offset); err == nil {
+		mem = cacheMemory(mem, uintptr(gaddr), int(gtype.Size()))
 	}
 
 	// Parse defer
@@ -373,7 +385,7 @@ func parseG(thread *Thread, gaddr uint64, deref bool) (*G, error) {
 	}
 	var deferPC uint64
 	// Dereference *defer pointer
-	deferAddrBytes, err := mem.readMemory(uintptr(deferAddr), thread.dbp.arch.PtrSize())
+	deferAddrBytes, err := mem.readMemory(uintptr(deferAddr), dbp.arch.PtrSize())
 	if err != nil {
 		return nil, fmt.Errorf("error derefing defer %s", err)
 	}
@@ -412,7 +424,7 @@ func parseG(thread *Thread, gaddr uint64, deref bool) (*G, error) {
 	if err != nil {
 		return nil, err
 	}
-	pc, err := readUintRaw(mem, uintptr(schedAddr+uint64(thread.dbp.arch.PtrSize())), 8)
+	pc, err := readUintRaw(mem, uintptr(schedAddr+uint64(dbp.arch.PtrSize())), 8)
 	if err != nil {
 		return nil, err
 	}
@@ -436,7 +448,7 @@ func parseG(thread *Thread, gaddr uint64, deref bool) (*G, error) {
 	if err != nil {
 		return nil, err
 	}
-	waitreason, _, err := readString(mem, thread.dbp.arch, uintptr(waitReasonAddr))
+	waitreason, _, err := readString(mem, dbp.arch, uintptr(waitReasonAddr))
 	if err != nil {
 		return nil, err
 	}
@@ -450,7 +462,7 @@ func parseG(thread *Thread, gaddr uint64, deref bool) (*G, error) {
 		return nil, err
 	}
 
-	f, l, fn := thread.dbp.goSymTable.PCToLine(pc)
+	f, l, fn := dbp.goSymTable.PCToLine(pc)
 	g := &G{
 		ID:         int(goid),
 		GoPC:       gopc,
@@ -460,7 +472,7 @@ func parseG(thread *Thread, gaddr uint64, deref bool) (*G, error) {
 		WaitReason: waitreason,
 		DeferPC:    deferPC,
 		Status:     atomicStatus,
-		dbp:        thread.dbp,
+		dbp:        dbp,
 	}
 	return g, nil
 }