*: function call injection for go 1.11

Implements the function call injection protocol introduced in go 1.11
by https://go-review.googlesource.com/c/go/+/109699.

This is only the basic support, see TODO comments in pkg/proc/fncall.go
for a list of missing features.

Updates #119

Documentation/cli/README.md

@@ -5,6 +5,7 @@ Command | Description
 [args](#args) | Print function arguments.
 [break](#break) | Sets a breakpoint.
 [breakpoints](#breakpoints) | Print out info for active breakpoints.
+[call](#call) | Resumes process, injecting a function call (EXPERIMENTAL!!!)
 [check](#check) | Creates a checkpoint at the current position.
 [checkpoints](#checkpoints) | Print out info for existing checkpoints.
 [clear](#clear) | Deletes breakpoint.
@@ -68,6 +69,27 @@ Print out info for active breakpoints.
 
 Aliases: bp
 
+## call
+Resumes process, injecting a function call (EXPERIMENTAL!!!)
+	
+Current limitations:
+- can only call package-level functions, no function pointers nor methods.
+- only things that have an address can be used as arguments (no literal
+  constants or results of evaluating some expressions).
+- only pointers to stack-allocated objects can be passed as argument.
+- no automatic type conversions are supported, including automatically
+  converting to an interface type.
+- functions can only be called on running goroutines that are not
+  executing the runtime.
+- the current goroutine needs to have at least 256 bytes of free space on
+  the stack.
+- functions can only be called when the goroutine is stopped at a safe
+  point.
+- calling a function will resume execution of all goroutines.
+- only supported on linux's native backend.
+
+
+
 ## check
 Creates a checkpoint at the current position.
 

Documentation/usage/dlv.md

@@ -38,6 +38,7 @@ Pass flags to the program you are debugging using `--`, for example:
 	lldbout		Copy output from debugserver/lldb to standard output
 	debuglineerr	Log recoverable errors reading .debug_line
 	rpc		Log all RPC messages
+	fncall		Log function call protocol
 Defaults to "debugger" when logging is enabled with --log.
       --wd string            Working directory for running the program. (default ".")
 ```

Documentation/usage/dlv_attach.md

@@ -38,6 +38,7 @@ dlv attach pid [executable]
 	lldbout		Copy output from debugserver/lldb to standard output
 	debuglineerr	Log recoverable errors reading .debug_line
 	rpc		Log all RPC messages
+	fncall		Log function call protocol
 Defaults to "debugger" when logging is enabled with --log.
       --wd string            Working directory for running the program. (default ".")
 ```

Documentation/usage/dlv_connect.md

@@ -33,6 +33,7 @@ dlv connect addr
 	lldbout		Copy output from debugserver/lldb to standard output
 	debuglineerr	Log recoverable errors reading .debug_line
 	rpc		Log all RPC messages
+	fncall		Log function call protocol
 Defaults to "debugger" when logging is enabled with --log.
       --wd string            Working directory for running the program. (default ".")
 ```

Documentation/usage/dlv_core.md

@@ -37,6 +37,7 @@ dlv core <executable> <core>
 	lldbout		Copy output from debugserver/lldb to standard output
 	debuglineerr	Log recoverable errors reading .debug_line
 	rpc		Log all RPC messages
+	fncall		Log function call protocol
 Defaults to "debugger" when logging is enabled with --log.
       --wd string            Working directory for running the program. (default ".")
 ```

Documentation/usage/dlv_debug.md

@@ -44,6 +44,7 @@ dlv debug [package]
 	lldbout		Copy output from debugserver/lldb to standard output
 	debuglineerr	Log recoverable errors reading .debug_line
 	rpc		Log all RPC messages
+	fncall		Log function call protocol
 Defaults to "debugger" when logging is enabled with --log.
       --wd string            Working directory for running the program. (default ".")
 ```

Documentation/usage/dlv_exec.md

@@ -38,6 +38,7 @@ dlv exec <path/to/binary>
 	lldbout		Copy output from debugserver/lldb to standard output
 	debuglineerr	Log recoverable errors reading .debug_line
 	rpc		Log all RPC messages
+	fncall		Log function call protocol
 Defaults to "debugger" when logging is enabled with --log.
       --wd string            Working directory for running the program. (default ".")
 ```

Documentation/usage/dlv_replay.md

@@ -37,6 +37,7 @@ dlv replay [trace directory]
 	lldbout		Copy output from debugserver/lldb to standard output
 	debuglineerr	Log recoverable errors reading .debug_line
 	rpc		Log all RPC messages
+	fncall		Log function call protocol
 Defaults to "debugger" when logging is enabled with --log.
       --wd string            Working directory for running the program. (default ".")
 ```

Documentation/usage/dlv_run.md

@@ -33,6 +33,7 @@ dlv run
 	lldbout		Copy output from debugserver/lldb to standard output
 	debuglineerr	Log recoverable errors reading .debug_line
 	rpc		Log all RPC messages
+	fncall		Log function call protocol
 Defaults to "debugger" when logging is enabled with --log.
       --wd string            Working directory for running the program. (default ".")
 ```

Documentation/usage/dlv_test.md

@@ -44,6 +44,7 @@ dlv test [package]
 	lldbout		Copy output from debugserver/lldb to standard output
 	debuglineerr	Log recoverable errors reading .debug_line
 	rpc		Log all RPC messages
+	fncall		Log function call protocol
 Defaults to "debugger" when logging is enabled with --log.
       --wd string            Working directory for running the program. (default ".")
 ```

Documentation/usage/dlv_trace.md

@@ -46,6 +46,7 @@ dlv trace [package] regexp
 	lldbout		Copy output from debugserver/lldb to standard output
 	debuglineerr	Log recoverable errors reading .debug_line
 	rpc		Log all RPC messages
+	fncall		Log function call protocol
 Defaults to "debugger" when logging is enabled with --log.
       --wd string            Working directory for running the program. (default ".")
 ```

Documentation/usage/dlv_version.md

@@ -33,6 +33,7 @@ dlv version
 	lldbout		Copy output from debugserver/lldb to standard output
 	debuglineerr	Log recoverable errors reading .debug_line
 	rpc		Log all RPC messages
+	fncall		Log function call protocol
 Defaults to "debugger" when logging is enabled with --log.
       --wd string            Working directory for running the program. (default ".")
 ```

_fixtures/fncall.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"fmt"
+	"runtime"
+)
+
+func callstacktrace() (stacktrace string) {
+	for skip := 0; ; skip++ {
+		pc, file, line, ok := runtime.Caller(skip)
+		if !ok {
+			break
+		}
+		fn := runtime.FuncForPC(pc)
+		stacktrace += fmt.Sprintf("in %s at %s:%d\n", fn.Name(), file, line)
+	}
+	return stacktrace
+}
+
+func call1(a, b int) int {
+	fmt.Printf("first: %d second: %d\n", a, b)
+	return a + b
+}
+
+func callpanic() {
+	fmt.Printf("about to panic\n")
+	panic("callpanic panicked")
+}
+
+var zero = 0
+
+func main() {
+	one, two := 1, 2
+	runtime.Breakpoint()
+	call1(one, two)
+	fmt.Println(one, two, zero, callpanic, callstacktrace)
+}

cmd/dlv/cmds/commands.go

@@ -95,6 +95,7 @@ func New(docCall bool) *cobra.Command {
 	lldbout		Copy output from debugserver/lldb to standard output
 	debuglineerr	Log recoverable errors reading .debug_line
 	rpc		Log all RPC messages
+	fncall		Log function call protocol
 Defaults to "debugger" when logging is enabled with --log.`)
 	RootCommand.PersistentFlags().BoolVarP(&Headless, "headless", "", false, "Run debug server only, in headless mode.")
 	RootCommand.PersistentFlags().BoolVarP(&AcceptMulti, "accept-multiclient", "", false, "Allows a headless server to accept multiple client connections. Note that the server API is not reentrant and clients will have to coordinate.")

pkg/logflags/logflags.go

@@ -12,6 +12,7 @@ var gdbWire = false
 var lldbServerOutput = false
 var debugLineErrors = false
 var rpc = false
+var fnCall = false
 
 // GdbWire returns true if the gdbserial package should log all the packets
 // exchanged with the stub.
@@ -41,6 +42,11 @@ func RPC() bool {
 	return rpc
 }
 
+// FnCall returns true if the function call protocol should be logged.
+func FnCall() bool {
+	return fnCall
+}
+
 var errLogstrWithoutLog = errors.New("--log-output specified without --log")
 
 // Setup sets debugger flags based on the contents of logstr.
@@ -69,6 +75,8 @@ func Setup(logFlag bool, logstr string) error {
 			debugLineErrors = true
 		case "rpc":
 			rpc = true
+		case "fncall":
+			fnCall = true
 		}
 	}
 	return nil

pkg/proc/bininfo.go

@@ -474,6 +474,11 @@ func (bi *BinaryInfo) Producer() string {
 	return ""
 }
 
+// Type returns the Dwarf type entry at `offset`.
+func (bi *BinaryInfo) Type(offset dwarf.Offset) (godwarf.Type, error) {
+	return godwarf.ReadType(bi.dwarf, offset, bi.typeCache)
+}
+
 // ELF ///////////////////////////////////////////////////////////////
 
 // This error is used in openSeparateDebugInfo to signal there's no

pkg/proc/breakpoints.go

@@ -1,7 +1,6 @@
 package proc
 
 import (
-	"debug/dwarf"
 	"errors"
 	"fmt"
 	"go/ast"
@@ -386,8 +385,6 @@ func (rbpi *returnBreakpointInfo) Collect(thread Thread) []*Variable {
 		return nil
 	}
 
-	bi := thread.BinInfo()
-
 	g, err := GetG(thread)
 	if err != nil {
 		return returnInfoError("could not get g", err, thread)
@@ -408,22 +405,12 @@ func (rbpi *returnBreakpointInfo) Collect(thread Thread) []*Variable {
 		return nil
 	}
 
-	// Alter the eval scope so that it looks like we are at the entry point of
-	// the function we just returned from.
-	// This involves changing the location (PC, function...) as well as
-	// anything related to the stack pointer (SP, CFA, FrameBase).
-	scope.PC = rbpi.fn.Entry
-	scope.Fn = rbpi.fn
-	scope.File, scope.Line, _ = bi.PCToLine(rbpi.fn.Entry)
-	scope.Regs.CFA = rbpi.frameOffset + int64(g.stackhi)
-	scope.Regs.Regs[scope.Regs.SPRegNum].Uint64Val = uint64(rbpi.spOffset + int64(g.stackhi))
-
-	bi.dwarfReader.Seek(rbpi.fn.offset)
-	e, err := bi.dwarfReader.Next()
+	oldFrameOffset := rbpi.frameOffset + int64(g.stackhi)
+	oldSP := uint64(rbpi.spOffset + int64(g.stackhi))
+	err = fakeFunctionEntryScope(scope, rbpi.fn, oldFrameOffset, oldSP)
 	if err != nil {
 		return returnInfoError("could not read function entry", err, thread)
 	}
-	scope.Regs.FrameBase, _, _, _ = bi.Location(e, dwarf.AttrFrameBase, scope.PC, scope.Regs)
 
 	vars, err := scope.Locals()
 	if err != nil {

pkg/proc/core/core.go

@@ -239,6 +239,10 @@ func (t *Thread) Registers(floatingPoint bool) (proc.Registers, error) {
 	return r, nil
 }
 
+func (t *Thread) RestoreRegisters(proc.SavedRegisters) error {
+	return errors.New("not supported")
+}
+
 func (t *Thread) Arch() proc.Arch {
 	return t.p.bi.Arch
 }
@@ -263,6 +267,14 @@ func (t *Thread) Common() *proc.CommonThread {
 	return &t.common
 }
 
+func (t *Thread) SetPC(uint64) error {
+	return errors.New("not supported")
+}
+
+func (t *Thread) SetSP(uint64) error {
+	return errors.New("not supported")
+}
+
 func (p *Process) Breakpoints() *proc.BreakpointMap {
 	return &p.breakpoints
 }
@@ -409,3 +421,7 @@ func (r *Registers) Slice() []proc.Register {
 	out = append(out, r.fpregs...)
 	return out
 }
+
+func (r *Registers) Save() proc.SavedRegisters {
+	return r
+}

pkg/proc/core/linux_amd64_core.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"debug/elf"
 	"encoding/binary"
-	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -237,10 +236,6 @@ func (r *LinuxCoreRegisters) Get(n int) (uint64, error) {
 	return 0, proc.UnknownRegisterError
 }
 
-func (r *LinuxCoreRegisters) SetPC(proc.Thread, uint64) error {
-	return errors.New("not supported")
-}
-
 // readCore reads a core file from corePath corresponding to the executable at
 // exePath. For details on the Linux ELF core format, see:
 // http://www.gabriel.urdhr.fr/2015/05/29/core-file/,

pkg/proc/fncall.go

@@ -0,0 +1,545 @@
+package proc
+
+import (
+	"debug/dwarf"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"go/ast"
+	"go/constant"
+	"go/parser"
+	"reflect"
+	"sort"
+
+	"github.com/derekparker/delve/pkg/dwarf/godwarf"
+	"github.com/derekparker/delve/pkg/dwarf/op"
+	"github.com/derekparker/delve/pkg/dwarf/reader"
+	"github.com/derekparker/delve/pkg/logflags"
+	"github.com/sirupsen/logrus"
+	"golang.org/x/arch/x86/x86asm"
+)
+
+// This file implements the function call injection introduced in go1.11.
+//
+// The protocol is described in $GOROOT/src/runtime/asm_amd64.s in the
+// comments for function runtime·debugCallV1.
+//
+// There are two main entry points here. The first one is CallFunction which
+// evaluates a function call expression, sets up the function call on the
+// selected goroutine and resumes execution of the process.
+//
+// The second one is (*FunctionCallState).step() which is called every time
+// the process stops at a breakpoint inside one of the debug injcetion
+// functions.
+
+const (
+	debugCallFunctionNamePrefix1 = "debugCall"
+	debugCallFunctionNamePrefix2 = "runtime.debugCall"
+	debugCallFunctionName        = "runtime.debugCallV1"
+)
+
+var (
+	ErrFuncCallUnsupported        = errors.New("function calls not supported by this version of Go")
+	ErrFuncCallUnsupportedBackend = errors.New("backend does not support function calls")
+	ErrFuncCallInProgress         = errors.New("cannot call function while another function call is already in progress")
+	ErrNotACallExpr               = errors.New("not a function call")
+	ErrNoGoroutine                = errors.New("no goroutine selected")
+	ErrGoroutineNotRunning        = errors.New("selected goroutine not running")
+	ErrNotEnoughStack             = errors.New("not enough stack space")
+	ErrTooManyArguments           = errors.New("too many arguments")
+	ErrNotEnoughArguments         = errors.New("not enough arguments")
+	ErrNoAddrUnsupported          = errors.New("arguments to a function call must have an address")
+	ErrNotAGoFunction             = errors.New("not a Go function")
+)
+
+type functionCallState struct {
+	// inProgress is true if a function call is in progress
+	inProgress bool
+	// finished is true if the function call terminated
+	finished bool
+	// savedRegs contains the saved registers
+	savedRegs SavedRegisters
+	// expr contains an expression describing the current function call
+	expr string
+	// err contains a saved error
+	err error
+	// fn is the function that is being called
+	fn *Function
+	// argmem contains the argument frame of this function call
+	argmem []byte
+	// retvars contains the return variables after the function call terminates without panic'ing
+	retvars []*Variable
+	// retLoadCfg is the load configuration used to load return values
+	retLoadCfg *LoadConfig
+	// panicvar is a variable used to store the value of the panic, if the
+	// called function panics.
+	panicvar *Variable
+}
+
+// CallFunction starts a debugger injected function call on the current thread of p.
+// See runtime.debugCallV1 in $GOROOT/src/runtime/asm_amd64.s for a
+// description of the protocol.
+func CallFunction(p Process, expr string, retLoadCfg *LoadConfig) error {
+	bi := p.BinInfo()
+	if !p.Common().fncallEnabled {
+		return ErrFuncCallUnsupportedBackend
+	}
+	fncall := &p.Common().fncallState
+	if fncall.inProgress {
+		return ErrFuncCallInProgress
+	}
+
+	*fncall = functionCallState{}
+
+	dbgcallfn := bi.LookupFunc[debugCallFunctionName]
+	if dbgcallfn == nil {
+		return ErrFuncCallUnsupported
+	}
+
+	// check that the selected goroutine is running
+	g := p.SelectedGoroutine()
+	if g == nil {
+		return ErrNoGoroutine
+	}
+	if g.Status != Grunning || g.Thread == nil {
+		return ErrGoroutineNotRunning
+	}
+
+	// check that there are at least 256 bytes free on the stack
+	regs, err := g.Thread.Registers(true)
+	if err != nil {
+		return err
+	}
+	if regs.SP()-256 <= g.stacklo {
+		return ErrNotEnoughStack
+	}
+	_, err = regs.Get(int(x86asm.RAX))
+	if err != nil {
+		return ErrFuncCallUnsupportedBackend
+	}
+
+	fn, argvars, err := funcCallEvalExpr(p, expr)
+	if err != nil {
+		return err
+	}
+
+	argmem, err := funcCallArgFrame(fn, argvars, g, bi)
+	if err != nil {
+		return err
+	}
+
+	if err := callOP(bi, g.Thread, regs, dbgcallfn.Entry); err != nil {
+		return err
+	}
+	// write the desired argument frame size at SP-(2*pointer_size) (the extra pointer is the saved PC)
+	if err := writePointer(bi, g.Thread, regs.SP()-3*uint64(bi.Arch.PtrSize()), uint64(len(argmem))); err != nil {
+		return err
+	}
+
+	fncall.inProgress = true
+	fncall.savedRegs = regs.Save()
+	fncall.expr = expr
+	fncall.fn = fn
+	fncall.argmem = argmem
+	fncall.retLoadCfg = retLoadCfg
+
+	fncallLog("function call initiated %v frame size %d\n", fn, len(argmem))
+
+	return Continue(p)
+}
+
+func fncallLog(fmtstr string, args ...interface{}) {
+	if !logflags.FnCall() {
+		return
+	}
+	logrus.WithFields(logrus.Fields{"layer": "proc", "kind": "fncall"}).Debugf(fmtstr, args...)
+}
+
+// writePointer writes val as an architecture pointer at addr in mem.
+func writePointer(bi *BinaryInfo, mem MemoryReadWriter, addr, val uint64) error {
+	ptrbuf := make([]byte, bi.Arch.PtrSize())
+
+	// TODO: use target architecture endianness instead of LittleEndian
+	switch len(ptrbuf) {
+	case 4:
+		binary.LittleEndian.PutUint32(ptrbuf, uint32(val))
+	case 8:
+		binary.LittleEndian.PutUint64(ptrbuf, val)
+	default:
+		panic(fmt.Errorf("unsupported pointer size %d", len(ptrbuf)))
+	}
+	_, err := mem.WriteMemory(uintptr(addr), ptrbuf)
+	return err
+}
+
+// callOP simulates a call instruction on the given thread:
+// * pushes the current value of PC on the stack (adjusting SP)
+// * changes the value of PC to callAddr
+// Note: regs are NOT updated!
+func callOP(bi *BinaryInfo, thread Thread, regs Registers, callAddr uint64) error {
+	sp := regs.SP()
+	// push PC on the stack
+	sp -= uint64(bi.Arch.PtrSize())
+	if err := thread.SetSP(sp); err != nil {
+		return err
+	}
+	if err := writePointer(bi, thread, sp, regs.PC()); err != nil {
+		return err
+	}
+	return thread.SetPC(callAddr)
+}
+
+// funcCallEvalExpr evaluates expr, which must be a function call, returns
+// the function being called and its arguments.
+func funcCallEvalExpr(p Process, expr string) (fn *Function, argvars []*Variable, err error) {
+	bi := p.BinInfo()
+	scope, err := GoroutineScope(p.CurrentThread())
+	if err != nil {
+		return nil, nil, err
+	}
+
+	t, err := parser.ParseExpr(expr)
+	if err != nil {
+		return nil, nil, err
+	}
+	callexpr, iscall := t.(*ast.CallExpr)
+	if !iscall {
+		return nil, nil, ErrNotACallExpr
+	}
+
+	//TODO(aarzilli): must evaluate <var>.<method> and treat them appropriately
+	fnvar, err := scope.evalAST(callexpr.Fun)
+	if err != nil {
+		return nil, nil, err
+	}
+	if fnvar.Kind != reflect.Func {
+		return nil, nil, fmt.Errorf("expression %q is not a function", exprToString(callexpr.Fun))
+	}
+	fn = bi.PCToFunc(uint64(fnvar.Base))
+	if fn == nil {
+		return nil, nil, fmt.Errorf("could not find DIE for function %q", exprToString(callexpr.Fun))
+	}
+	if !fn.cu.isgo {
+		return nil, nil, ErrNotAGoFunction
+	}
+
+	argvars = make([]*Variable, len(callexpr.Args))
+	for i := range callexpr.Args {
+		argvars[i], err = scope.evalAST(callexpr.Args[i])
+		if err != nil {
+			return nil, nil, err
+		}
+		argvars[i].Name = exprToString(callexpr.Args[i])
+	}
+
+	return fn, argvars, nil
+}
+
+type funcCallArg struct {
+	name string
+	typ  godwarf.Type
+	off  int64
+}
+
+// funcCallArgFrame checks type and pointer escaping for the arguments and
+// returns the argument frame.
+func funcCallArgFrame(fn *Function, actualArgs []*Variable, g *G, bi *BinaryInfo) (argmem []byte, err error) {
+	const CFA = 0x1000
+	vrdr := reader.Variables(bi.dwarf, fn.offset, fn.Entry, int(^uint(0)>>1), false)
+	formalArgs := []funcCallArg{}
+
+	// typechecks arguments, calculates argument frame size
+	argFrameSize := int64(0)
+	for vrdr.Next() {
+		e := vrdr.Entry()
+		if e.Tag != dwarf.TagFormalParameter {
+			continue
+		}
+		entry, argname, typ, err := readVarEntry(e, bi)
+		if err != nil {
+			return nil, err
+		}
+		typ = resolveTypedef(typ)
+		locprog, ok := entry.Val(dwarf.AttrLocation).([]byte)
+		if !ok {
+			return nil, fmt.Errorf("unsupported location expression for argument %s", argname)
+		}
+		off, _, err := op.ExecuteStackProgram(op.DwarfRegisters{CFA: CFA, FrameBase: CFA}, locprog)
+		if err != nil {
+			return nil, fmt.Errorf("unsupported location expression for argument %s: %v", argname, err)
+		}
+
+		off -= CFA
+
+		if e := off + typ.Size(); e > argFrameSize {
+			argFrameSize = e
+		}
+
+		if isret, _ := entry.Val(dwarf.AttrVarParam).(bool); !isret {
+			formalArgs = append(formalArgs, funcCallArg{name: argname, typ: typ, off: off})
+		}
+	}
+	if err := vrdr.Err(); err != nil {
+		return nil, fmt.Errorf("DWARF read error: %v", err)
+	}
+	if len(actualArgs) > len(formalArgs) {
+		return nil, ErrTooManyArguments
+	}
+	if len(actualArgs) < len(formalArgs) {
+		return nil, ErrNotEnoughArguments
+	}
+
+	sort.Slice(formalArgs, func(i, j int) bool {
+		return formalArgs[i].off < formalArgs[j].off
+	})
+
+	// constructs arguments frame
+	argmem = make([]byte, argFrameSize)
+	for i := range formalArgs {
+		formalArg := &formalArgs[i]
+		actualArg := actualArgs[i]
+
+		if actualArg.Addr == 0 {
+			//TODO(aarzilli): at least some of this needs to be supported
+			return nil, ErrNoAddrUnsupported
+		}
+
+		if actualArg.RealType != formalArg.typ {
+			return nil, fmt.Errorf("cannot use %s (type %s) as type %s in argument to %s", actualArg.Name, actualArg.DwarfType.String(), formalArg.typ.String(), fn.Name)
+		}
+
+		//TODO(aarzilli): only apply the escapeCheck to leaking parameters.
+		if err := escapeCheck(actualArg, formalArg.name, g); err != nil {
+			return nil, fmt.Errorf("can not pass %s to %s: %v", actualArg.Name, formalArg.name, err)
+		}
+
+		//TODO(aarzilli): automatic type conversions
+		//TODO(aarzilli): automatic wrapping in interfaces?
+
+		buf := make([]byte, actualArg.RealType.Size())
+		sz, err := actualArg.mem.ReadMemory(buf, actualArg.Addr)
+		if err != nil {
+			return nil, fmt.Errorf("could not read argument %s: %v", actualArg.Name, err)
+		}
+		if int64(sz) != actualArg.RealType.Size() {
+			return nil, fmt.Errorf("short read for argument %s: %d != %d %x", actualArg.Name, sz, actualArg.RealType.Size(), buf)
+		}
+
+		copy(argmem[formalArg.off:], buf)
+	}
+
+	return argmem, nil
+}
+
+func escapeCheck(v *Variable, name string, g *G) error {
+	switch v.Kind {
+	case reflect.Ptr:
+		w := v.maybeDereference()
+		return escapeCheckPointer(w.Addr, name, g)
+	case reflect.Chan, reflect.String, reflect.Slice:
+		return escapeCheckPointer(v.Base, name, g)
+	case reflect.Map:
+		sv := v.clone()
+		sv.RealType = resolveTypedef(&(v.RealType.(*godwarf.MapType).TypedefType))
+		sv = sv.maybeDereference()
+		return escapeCheckPointer(sv.Addr, name, g)
+	case reflect.Struct:
+		t := v.RealType.(*godwarf.StructType)
+		for _, field := range t.Field {
+			fv, _ := v.toField(field)
+			if err := escapeCheck(fv, fmt.Sprintf("%s.%s", name, field.Name), g); err != nil {
+				return err
+			}
+		}
+	case reflect.Array:
+		for i := int64(0); i < v.Len; i++ {
+			sv, _ := v.sliceAccess(int(i))
+			if err := escapeCheck(sv, fmt.Sprintf("%s[%d]", name, i), g); err != nil {
+				return err
+			}
+		}
+	case reflect.Func:
+		//TODO(aarzilli): check closure argument?
+	}
+
+	return nil
+}
+
+func escapeCheckPointer(addr uintptr, name string, g *G) error {
+	if uint64(addr) >= g.stacklo && uint64(addr) < g.stackhi {
+		return fmt.Errorf("stack object passed to escaping pointer %s", name)
+	}
+	return nil
+}
+
+const (
+	debugCallAXPrecheckFailed   = 8
+	debugCallAXCompleteCall     = 0
+	debugCallAXReadReturn       = 1
+	debugCallAXReadPanic        = 2
+	debugCallAXRestoreRegisters = 16
+)
+
+func (fncall *functionCallState) step(p Process) {
+	bi := p.BinInfo()
+
+	thread := p.CurrentThread()
+	regs, err := thread.Registers(false)
+	if err != nil {
+		fncall.err = err
+		fncall.finished = true
+		fncall.inProgress = false
+		return
+	}
+
+	rax, _ := regs.Get(int(x86asm.RAX))
+
+	if logflags.FnCall() {
+		loc, _ := thread.Location()
+		var pc uint64
+		var fnname string
+		if loc != nil {
+			pc = loc.PC
+			if loc.Fn != nil {
+				fnname = loc.Fn.Name
+			}
+		}
+		fncallLog("function call interrupt rax=%#x (PC=%#x in %s)\n", rax, pc, fnname)
+	}
+
+	switch rax {
+	case debugCallAXPrecheckFailed:
+		// get error from top of the stack and return it to user
+		errvar, err := readTopstackVariable(thread, regs, "string", loadFullValue)
+		if err != nil {
+			fncall.err = fmt.Errorf("could not get precheck error reason: %v", err)
+			break
+		}
+		errvar.Name = "err"
+		fncall.err = fmt.Errorf("%v", constant.StringVal(errvar.Value))
+
+	case debugCallAXCompleteCall:
+		// write arguments to the stack, call final function
+		n, err := thread.WriteMemory(uintptr(regs.SP()), fncall.argmem)
+		if err != nil {
+			fncall.err = fmt.Errorf("could not write arguments: %v", err)
+		}
+		if n != len(fncall.argmem) {
+			fncall.err = fmt.Errorf("short argument write: %d %d", n, len(fncall.argmem))
+		}
+		//TODO(aarzilli): if fncall.fn is a function closure CX needs to be set here
+		callOP(bi, thread, regs, fncall.fn.Entry)
+
+	case debugCallAXRestoreRegisters:
+		// runtime requests that we restore the registers (all except pc and sp),
+		// this is also the last step of the function call protocol.
+		fncall.finished = true
+		pc, sp := regs.PC(), regs.SP()
+		if err := thread.RestoreRegisters(fncall.savedRegs); err != nil {
+			fncall.err = fmt.Errorf("could not restore registers: %v", err)
+		}
+		if err := thread.SetPC(pc); err != nil {
+			fncall.err = fmt.Errorf("could not restore PC: %v", err)
+		}
+		if err := thread.SetSP(sp); err != nil {
+			fncall.err = fmt.Errorf("could not restore SP: %v", err)
+		}
+		if err := stepInstructionOut(p, thread, debugCallFunctionName, debugCallFunctionName); err != nil {
+			fncall.err = fmt.Errorf("could not step out of %s: %v", debugCallFunctionName, err)
+		}
+
+	case debugCallAXReadReturn:
+		// read return arguments from stack
+		if fncall.retLoadCfg == nil || fncall.panicvar != nil {
+			break
+		}
+		scope, err := ThreadScope(thread)
+		if err != nil {
+			fncall.err = fmt.Errorf("could not get return values: %v", err)
+			break
+		}
+
+		// pretend we are still inside the function we called
+		fakeFunctionEntryScope(scope, fncall.fn, int64(regs.SP()), regs.SP()-uint64(bi.Arch.PtrSize()))
+
+		fncall.retvars, err = scope.Locals()
+		if err != nil {
+			fncall.err = fmt.Errorf("could not get return values: %v", err)
+			break
+		}
+		fncall.retvars = filterVariables(fncall.retvars, func(v *Variable) bool {
+			return (v.Flags & VariableReturnArgument) != 0
+		})
+
+		loadValues(fncall.retvars, *fncall.retLoadCfg)
+
+	case debugCallAXReadPanic:
+		// read panic value from stack
+		if fncall.retLoadCfg == nil {
+			return
+		}
+		fncall.panicvar, err = readTopstackVariable(thread, regs, "interface {}", *fncall.retLoadCfg)
+		if err != nil {
+			fncall.err = fmt.Errorf("could not get panic: %v", err)
+			break
+		}
+		fncall.panicvar.Name = "~panic"
+		fncall.panicvar.loadValue(*fncall.retLoadCfg)
+		if fncall.panicvar.Unreadable != nil {
+			fncall.err = fmt.Errorf("could not get panic: %v", fncall.panicvar.Unreadable)
+			break
+		}
+
+	default:
+		// Got an unknown AX value, this is probably bad but the safest thing
+		// possible is to ignore it and hope it didn't matter.
+		fncallLog("unknown value of AX %#x", rax)
+	}
+}
+
+func readTopstackVariable(thread Thread, regs Registers, typename string, loadCfg LoadConfig) (*Variable, error) {
+	bi := thread.BinInfo()
+	scope, err := ThreadScope(thread)
+	if err != nil {
+		return nil, err
+	}
+	typ, err := bi.findType(typename)
+	if err != nil {
+		return nil, err
+	}
+	v := scope.newVariable("", uintptr(regs.SP()), typ, scope.Mem)
+	v.loadValue(loadCfg)
+	if v.Unreadable != nil {
+		return nil, v.Unreadable
+	}
+	return v, nil
+}
+
+// fakeEntryScope alters scope to pretend that we are at the entry point of
+// fn and CFA and SP are the ones passed as argument.
+// This function is used to create a scope for a call frame that doesn't
+// exist anymore, to read the return variables of an injected function call,
+// or after a stepout command.
+func fakeFunctionEntryScope(scope *EvalScope, fn *Function, cfa int64, sp uint64) error {
+	scope.PC = fn.Entry
+	scope.Fn = fn
+	scope.File, scope.Line, _ = scope.BinInfo.PCToLine(fn.Entry)
+
+	scope.Regs.CFA = cfa
+	scope.Regs.Regs[scope.Regs.SPRegNum].Uint64Val = sp
+
+	scope.BinInfo.dwarfReader.Seek(fn.offset)
+	e, err := scope.BinInfo.dwarfReader.Next()
+	if err != nil {
+		return err
+	}
+	scope.Regs.FrameBase, _, _, _ = scope.BinInfo.Location(e, dwarf.AttrFrameBase, scope.PC, scope.Regs)
+	return nil
+}
+
+func (fncall *functionCallState) returnValues() []*Variable {
+	if fncall.panicvar != nil {
+		return []*Variable{fncall.panicvar}
+	}
+	return fncall.retvars
+}

pkg/proc/gdbserial/gdbserver.go

@@ -1197,6 +1197,11 @@ func (t *Thread) Registers(floatingPoint bool) (proc.Registers, error) {
 	return &t.regs, nil
 }
 
+func (t *Thread) RestoreRegisters(regs proc.SavedRegisters) error {
+	//TODO(aarzilli): implement
+	return errors.New("not implemented")
+}
+
 func (t *Thread) Arch() proc.Arch {
 	return t.p.bi.Arch
 }
@@ -1279,25 +1284,29 @@ func (p *Process) loadGInstr() []byte {
 	return buf.Bytes()
 }
 
+func (regs *gdbRegisters) init(regsInfo []gdbRegisterInfo) {
+	regs.regs = make(map[string]gdbRegister)
+	regs.regsInfo = regsInfo
+
+	regsz := 0
+	for _, reginfo := range regsInfo {
+		if endoff := reginfo.Offset + (reginfo.Bitsize / 8); endoff > regsz {
+			regsz = endoff
+		}
+	}
+	regs.buf = make([]byte, regsz)
+	for _, reginfo := range regsInfo {
+		regs.regs[reginfo.Name] = gdbRegister{regnum: reginfo.Regnum, value: regs.buf[reginfo.Offset : reginfo.Offset+reginfo.Bitsize/8]}
+	}
+}
+
 // reloadRegisters loads the current value of the thread's registers.
 // It will also load the address of the thread's G.
 // Loading the address of G can be done in one of two ways reloadGAlloc, if
 // the stub can allocate memory, or reloadGAtPC, if the stub can't.
 func (t *Thread) reloadRegisters() error {
 	if t.regs.regs == nil {
-		t.regs.regs = make(map[string]gdbRegister)
-		t.regs.regsInfo = t.p.conn.regsInfo
-
-		regsz := 0
-		for _, reginfo := range t.p.conn.regsInfo {
-			if endoff := reginfo.Offset + (reginfo.Bitsize / 8); endoff > regsz {
-				regsz = endoff
-			}
-		}
-		t.regs.buf = make([]byte, regsz)
-		for _, reginfo := range t.p.conn.regsInfo {
-			t.regs.regs[reginfo.Name] = gdbRegister{regnum: reginfo.Regnum, value: t.regs.buf[reginfo.Offset : reginfo.Offset+reginfo.Bitsize/8]}
-		}
+		t.regs.init(t.p.conn.regsInfo)
 	}
 
 	if t.p.gcmdok {
@@ -1503,7 +1512,7 @@ func (thread *Thread) SetCurrentBreakpoint() error {
 	pc := regs.PC()
 	if bp, ok := thread.p.FindBreakpoint(pc); ok {
 		if thread.regs.PC() != bp.Addr {
-			if err := thread.regs.SetPC(thread, bp.Addr); err != nil {
+			if err := thread.SetPC(bp.Addr); err != nil {
 				return err
 			}
 		}
@@ -1529,6 +1538,9 @@ func (regs *gdbRegisters) setPC(value uint64) {
 func (regs *gdbRegisters) SP() uint64 {
 	return binary.LittleEndian.Uint64(regs.regs[regnameSP].value)
 }
+func (regs *gdbRegisters) setSP(value uint64) {
+	binary.LittleEndian.PutUint64(regs.regs[regnameSP].value, value)
+}
 
 func (regs *gdbRegisters) BP() uint64 {
 	return binary.LittleEndian.Uint64(regs.regs[regnameBP].value)
@@ -1715,13 +1727,21 @@ func (regs *gdbRegisters) Get(n int) (uint64, error) {
 	return 0, proc.UnknownRegisterError
 }
 
-func (regs *gdbRegisters) SetPC(thread proc.Thread, pc uint64) error {
-	regs.setPC(pc)
-	t := thread.(*Thread)
+func (t *Thread) SetPC(pc uint64) error {
+	t.regs.setPC(pc)
 	if t.p.gcmdok {
 		return t.p.conn.writeRegisters(t.strID, t.regs.buf)
 	}
-	reg := regs.regs[regnamePC]
+	reg := t.regs.regs[regnamePC]
+	return t.p.conn.writeRegister(t.strID, reg.regnum, reg.value)
+}
+
+func (t *Thread) SetSP(sp uint64) error {
+	t.regs.setSP(sp)
+	if t.p.gcmdok {
+		return t.p.conn.writeRegisters(t.strID, t.regs.buf)
+	}
+	reg := t.regs.regs[regnameSP]
 	return t.p.conn.writeRegister(t.strID, reg.regnum, reg.value)
 }
 
@@ -1766,3 +1786,10 @@ func (regs *gdbRegisters) Slice() []proc.Register {
 	}
 	return r
 }
+
+func (regs *gdbRegisters) Save() proc.SavedRegisters {
+	savedRegs := &gdbRegisters{}
+	savedRegs.init(regs.regsInfo)
+	copy(savedRegs.buf, regs.buf)
+	return savedRegs
+}

pkg/proc/interface.go

@@ -109,7 +109,13 @@ type BreakpointManipulation interface {
 // CommonProcess contains fields used by this package, common to all
 // implementations of the Process interface.
 type CommonProcess struct {
-	allGCache []*G
+	allGCache     []*G
+	fncallState   functionCallState
+	fncallEnabled bool
+}
+
+func NewCommonProcess(fncallEnabled bool) CommonProcess {
+	return CommonProcess{fncallEnabled: fncallEnabled}
 }
 
 // ClearAllGCache clears the cached contents of the cache for runtime.allgs.

pkg/proc/native/proc_linux.go

@@ -54,6 +54,7 @@ func Launch(cmd []string, wd string, foreground bool) (*Process, error) {
 		return nil, proc.NotExecutableErr
 	}
 	dbp := New(0)
+	dbp.common = proc.NewCommonProcess(true)
 	dbp.execPtraceFunc(func() {
 		process = exec.Command(cmd[0])
 		process.Args = cmd
@@ -87,6 +88,7 @@ func Launch(cmd []string, wd string, foreground bool) (*Process, error) {
 // Attach to an existing process with the given PID.
 func Attach(pid int) (*Process, error) {
 	dbp := New(pid)
+	dbp.common = proc.NewCommonProcess(true)
 
 	var err error
 	dbp.execPtraceFunc(func() { err = PtraceAttach(dbp.pid) })

pkg/proc/native/ptrace_linux.go

@@ -77,6 +77,7 @@ func PtraceGetRegset(tid int) (regset proc.LinuxX86Xstate, err error) {
 		err = nil
 	}
 
-	err = proc.LinuxX86XstateRead(xstateargs[:iov.Len], false, &regset)
+	regset.Xsave = xstateargs[:iov.Len]
+	err = proc.LinuxX86XstateRead(regset.Xsave, false, &regset)
 	return regset, err
 }

pkg/proc/native/registers_darwin_amd64.go

@@ -4,6 +4,7 @@ package native
 import "C"
 import (
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"unsafe"
 
@@ -112,8 +113,7 @@ func (r *Regs) GAddr() (uint64, bool) {
 }
 
 // SetPC sets the RIP register to the value specified by `pc`.
-func (r *Regs) SetPC(t proc.Thread, pc uint64) error {
-	thread := t.(*Thread)
+func (thread *Thread) SetPC(pc uint64) error {
 	kret := C.set_pc(thread.os.threadAct, C.uint64_t(pc))
 	if kret != C.KERN_SUCCESS {
 		return fmt.Errorf("could not set pc")
@@ -121,6 +121,11 @@ func (r *Regs) SetPC(t proc.Thread, pc uint64) error {
 	return nil
 }
 
+// SetSP sets the RSP register to the value specified by `pc`.
+func (thread *Thread) SetSP(sp uint64) error {
+	return errors.New("not implemented")
+}
+
 func (r *Regs) Get(n int) (uint64, error) {
 	reg := x86asm.Reg(n)
 	const (
@@ -358,18 +363,10 @@ func registers(thread *Thread, floatingPoint bool) (proc.Registers, error) {
 	return regs, nil
 }
 
-func (thread *Thread) saveRegisters() (proc.Registers, error) {
-	kret := C.get_registers(C.mach_port_name_t(thread.os.threadAct), &thread.os.registers)
-	if kret != C.KERN_SUCCESS {
-		return nil, fmt.Errorf("could not save register contents")
-	}
-	return &Regs{rip: uint64(thread.os.registers.__rip), rsp: uint64(thread.os.registers.__rsp)}, nil
+type savedRegisters struct {
 }
 
-func (thread *Thread) restoreRegisters() error {
-	kret := C.set_registers(C.mach_port_name_t(thread.os.threadAct), &thread.os.registers)
-	if kret != C.KERN_SUCCESS {
-		return fmt.Errorf("could not save register contents")
-	}
+func (r *Regs) Save() proc.SavedRegisters {
+	//TODO(aarzilli): implement this to support function calls
 	return nil
 }

pkg/proc/native/registers_linux_amd64.go

@@ -11,8 +11,9 @@ import (
 
 // Regs is a wrapper for sys.PtraceRegs.
 type Regs struct {
-	regs   *sys.PtraceRegs
-	fpregs []proc.Register
+	regs     *sys.PtraceRegs
+	fpregs   []proc.Register
+	fpregset *proc.LinuxX86Xstate
 }
 
 func (r *Regs) Slice() []proc.Register {
@@ -90,10 +91,27 @@ func (r *Regs) GAddr() (uint64, bool) {
 }
 
 // SetPC sets RIP to the value specified by 'pc'.
-func (r *Regs) SetPC(t proc.Thread, pc uint64) (err error) {
-	thread := t.(*Thread)
+func (thread *Thread) SetPC(pc uint64) error {
+	ir, err := registers(thread, false)
+	if err != nil {
+		return err
+	}
+	r := ir.(*Regs)
 	r.regs.SetPC(pc)
 	thread.dbp.execPtraceFunc(func() { err = sys.PtraceSetRegs(thread.ID, r.regs) })
+	return err
+}
+
+// SetSP sets RSP to the value specified by 'sp'
+func (thread *Thread) SetSP(sp uint64) (err error) {
+	var ir proc.Registers
+	ir, err = registers(thread, false)
+	if err != nil {
+		return err
+	}
+	r := ir.(*Regs)
+	r.regs.Rsp = sp
+	thread.dbp.execPtraceFunc(func() { err = sys.PtraceSetRegs(thread.ID, r.regs) })
 	return
 }
 
@@ -263,9 +281,11 @@ func registers(thread *Thread, floatingPoint bool) (proc.Registers, error) {
 	if err != nil {
 		return nil, err
 	}
-	r := &Regs{&regs, nil}
+	r := &Regs{&regs, nil, nil}
 	if floatingPoint {
-		r.fpregs, err = thread.fpRegisters()
+		var fpregset proc.LinuxX86Xstate
+		r.fpregs, fpregset, err = thread.fpRegisters()
+		r.fpregset = &fpregset
 		if err != nil {
 			return nil, err
 		}
@@ -283,8 +303,7 @@ const (
 	_XSAVE_SSE_REGION_LEN        = 416
 )
 
-func (thread *Thread) fpRegisters() (regs []proc.Register, err error) {
-	var fpregs proc.LinuxX86Xstate
+func (thread *Thread) fpRegisters() (regs []proc.Register, fpregs proc.LinuxX86Xstate, err error) {
 	thread.dbp.execPtraceFunc(func() { fpregs, err = PtraceGetRegset(thread.ID) })
 	regs = fpregs.Decode()
 	if err != nil {
@@ -292,3 +311,15 @@ func (thread *Thread) fpRegisters() (regs []proc.Register, err error) {
 	}
 	return
 }
+
+type savedRegisters struct {
+	regs   sys.PtraceRegs
+	fpregs proc.LinuxX86Xstate
+}
+
+func (r *Regs) Save() proc.SavedRegisters {
+	savedRegs := &savedRegisters{}
+	savedRegs.regs = *r.regs
+	savedRegs.fpregs = *r.fpregset
+	return savedRegs
+}

pkg/proc/native/registers_windows_amd64.go

@@ -131,8 +131,7 @@ func (r *Regs) GAddr() (uint64, bool) {
 }
 
 // SetPC sets the RIP register to the value specified by `pc`.
-func (r *Regs) SetPC(t proc.Thread, pc uint64) error {
-	thread := t.(*Thread)
+func (thread *Thread) SetPC(pc uint64) error {
 	context := newCONTEXT()
 	context.ContextFlags = _CONTEXT_ALL
 
@@ -146,6 +145,21 @@ func (r *Regs) SetPC(t proc.Thread, pc uint64) error {
 	return _SetThreadContext(thread.os.hThread, context)
 }
 
+// SetSP sets the RSP register to the value specified by `sp`.
+func (thread *Thread) SetSP(sp uint64) error {
+	context := newCONTEXT()
+	context.ContextFlags = _CONTEXT_ALL
+
+	err := _GetThreadContext(thread.os.hThread, context)
+	if err != nil {
+		return err
+	}
+
+	context.Rsp = sp
+
+	return _SetThreadContext(thread.os.hThread, context)
+}
+
 func (r *Regs) Get(n int) (uint64, error) {
 	reg := x86asm.Reg(n)
 	const (
@@ -350,10 +364,10 @@ func registers(thread *Thread, floatingPoint bool) (proc.Registers, error) {
 	return regs, nil
 }
 
-func (thread *Thread) saveRegisters() (proc.Registers, error) {
-	return nil, fmt.Errorf("not implemented: saveRegisters")
+type savedRegisters struct {
 }
 
-func (thread *Thread) restoreRegisters() error {
-	return fmt.Errorf("not implemented: restoreRegisters")
+func (r *Regs) Save() proc.SavedRegisters {
+	//TODO(aarzilli): implement this to support function calls
+	return nil
 }

pkg/proc/native/threads.go

@@ -1,6 +1,7 @@
 package native
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/derekparker/delve/pkg/proc"
@@ -106,15 +107,6 @@ func (thread *Thread) Common() *proc.CommonThread {
 	return &thread.common
 }
 
-// SetPC sets the PC for this thread.
-func (thread *Thread) SetPC(pc uint64) error {
-	regs, err := thread.Registers(false)
-	if err != nil {
-		return err
-	}
-	return regs.SetPC(thread, pc)
-}
-
 // SetCurrentBreakpoint sets the current breakpoint that this
 // thread is stopped at as CurrentBreakpoint on the thread struct.
 func (thread *Thread) SetCurrentBreakpoint() error {
@@ -159,6 +151,14 @@ func (t *Thread) Registers(floatingPoint bool) (proc.Registers, error) {
 	return registers(t, floatingPoint)
 }
 
+func (t *Thread) RestoreRegisters(savedRegs proc.SavedRegisters) error {
+	sr, ok := savedRegs.(*savedRegisters)
+	if !ok {
+		return errors.New("unknown saved register set")
+	}
+	return t.restoreRegisters(sr)
+}
+
 func (t *Thread) PC() (uint64, error) {
 	regs, err := t.Registers(false)
 	if err != nil {

pkg/proc/native/threads_darwin.go

@@ -4,6 +4,7 @@ package native
 // #include "proc_darwin.h"
 import "C"
 import (
+	"errors"
 	"fmt"
 	"unsafe"
 
@@ -144,3 +145,7 @@ func (t *Thread) ReadMemory(buf []byte, addr uintptr) (int, error) {
 	}
 	return len(buf), nil
 }
+
+func (t *Thread) restoreRegisters(sr *savedRegisters) error {
+	return errors.New("not implemented")
+}

pkg/proc/native/threads_linux.go

@@ -2,6 +2,8 @@ package native
 
 import (
 	"fmt"
+	"syscall"
+	"unsafe"
 
 	sys "golang.org/x/sys/unix"
 
@@ -80,18 +82,26 @@ func (t *Thread) Blocked() bool {
 	return false
 }
 
-func (t *Thread) saveRegisters() (proc.Registers, error) {
-	var err error
-	t.dbp.execPtraceFunc(func() { err = sys.PtraceGetRegs(t.ID, &t.os.registers) })
-	if err != nil {
-		return nil, fmt.Errorf("could not save register contents")
-	}
-	return &Regs{&t.os.registers, nil}, nil
-}
+func (t *Thread) restoreRegisters(sr *savedRegisters) error {
+	var restoreRegistersErr error
+	t.dbp.execPtraceFunc(func() {
+		restoreRegistersErr = sys.PtraceSetRegs(t.ID, &sr.regs)
+		if restoreRegistersErr != nil {
+			return
+		}
+		if sr.fpregs.Xsave != nil {
+			iov := sys.Iovec{Base: &sr.fpregs.Xsave[0], Len: uint64(len(sr.fpregs.Xsave))}
+			_, _, restoreRegistersErr = syscall.Syscall6(syscall.SYS_PTRACE, sys.PTRACE_SETREGSET, uintptr(t.ID), _NT_X86_XSTATE, uintptr(unsafe.Pointer(&iov)), 0, 0)
+			return
+		}
 
-func (t *Thread) restoreRegisters() (err error) {
-	t.dbp.execPtraceFunc(func() { err = sys.PtraceSetRegs(t.ID, &t.os.registers) })
-	return
+		_, _, restoreRegistersErr = syscall.Syscall6(syscall.SYS_PTRACE, sys.PTRACE_SETFPREGS, uintptr(t.ID), uintptr(0), uintptr(unsafe.Pointer(&sr.fpregs.PtraceFpRegs)), 0, 0)
+		return
+	})
+	if restoreRegistersErr == syscall.Errno(0) {
+		restoreRegistersErr = nil
+	}
+	return restoreRegistersErr
 }
 
 func (t *Thread) WriteMemory(addr uintptr, data []byte) (written int, err error) {
@@ -113,5 +123,8 @@ func (t *Thread) ReadMemory(data []byte, addr uintptr) (n int, err error) {
 		return
 	}
 	t.dbp.execPtraceFunc(func() { _, err = sys.PtracePeekData(t.ID, addr, data) })
+	if err == nil {
+		n = len(data)
+	}
 	return
 }

pkg/proc/native/threads_windows.go

@@ -149,3 +149,7 @@ func (t *Thread) ReadMemory(buf []byte, addr uintptr) (int, error) {
 	}
 	return int(count), err
 }
+
+func (t *Thread) restoreRegisters(sr *savedRegisters) error {
+	return errors.New("not implemented")
+}

pkg/proc/proc.go

@@ -8,6 +8,7 @@ import (
 	"go/token"
 	"path/filepath"
 	"strconv"
+	"strings"
 )
 
 var NotExecutableErr = errors.New("not an executable file")
@@ -135,26 +136,45 @@ func Continue(dbp Process) error {
 
 		switch {
 		case curbp.Breakpoint == nil:
-			// runtime.Breakpoint or manual stop
-			if recorded, _ := dbp.Recorded(); onRuntimeBreakpoint(curthread) && !recorded {
+			// runtime.Breakpoint, manual stop or debugCallV1-related stop
+			recorded, _ := dbp.Recorded()
+			if recorded {
+				return conditionErrors(threads)
+			}
+
+			loc, err := curthread.Location()
+			if err != nil || loc.Fn == nil {
+				return conditionErrors(threads)
+			}
+
+			switch {
+			case loc.Fn.Name == "runtime.breakpoint":
 				// Single-step current thread until we exit runtime.breakpoint and
 				// runtime.Breakpoint.
 				// On go < 1.8 it was sufficient to single-step twice on go1.8 a change
 				// to the compiler requires 4 steps.
-				for {
-					if err = curthread.StepInstruction(); err != nil {
-						return err
-					}
-					loc, err := curthread.Location()
-					if err != nil || loc.Fn == nil || (loc.Fn.Name != "runtime.breakpoint" && loc.Fn.Name != "runtime.Breakpoint") {
-						if g := dbp.SelectedGoroutine(); g != nil {
-							g.CurrentLoc = *loc
-						}
-						break
-					}
+				if err := stepInstructionOut(dbp, curthread, "runtime.breakpoint", "runtime.Breakpoint"); err != nil {
+					return err
 				}
+				return conditionErrors(threads)
+			case strings.HasPrefix(loc.Fn.Name, debugCallFunctionNamePrefix1) || strings.HasPrefix(loc.Fn.Name, debugCallFunctionNamePrefix2):
+				fncall := &dbp.Common().fncallState
+				if !fncall.inProgress {
+					return conditionErrors(threads)
+				}
+				fncall.step(dbp)
+				// only stop execution if the function call finished
+				if fncall.finished {
+					fncall.inProgress = false
+					if fncall.err != nil {
+						return fncall.err
+					}
+					curthread.Common().returnValues = fncall.returnValues()
+					return conditionErrors(threads)
+				}
+			default:
+				return conditionErrors(threads)
 			}
-			return conditionErrors(threads)
 		case curbp.Active && curbp.Internal:
 			if curbp.Kind == StepBreakpoint {
 				// See description of proc.(*Process).next for the meaning of StepBreakpoints
@@ -239,6 +259,25 @@ func pickCurrentThread(dbp Process, trapthread Thread, threads []Thread) error {
 	return dbp.SwitchThread(trapthread.ThreadID())
 }
 
+// stepInstructionOut repeatedly calls StepInstruction until the current
+// function is neither fnname1 or fnname2.
+// This function is used to step out of runtime.Breakpoint as well as
+// runtime.debugCallV1.
+func stepInstructionOut(dbp Process, curthread Thread, fnname1, fnname2 string) error {
+	for {
+		if err := curthread.StepInstruction(); err != nil {
+			return err
+		}
+		loc, err := curthread.Location()
+		if err != nil || loc.Fn == nil || (loc.Fn.Name != fnname1 && loc.Fn.Name != fnname2) {
+			if g := dbp.SelectedGoroutine(); g != nil {
+				g.CurrentLoc = *loc
+			}
+			return nil
+		}
+	}
+}
+
 // Step will continue until another source line is reached.
 // Will step into functions.
 func Step(dbp Process) (err error) {
@@ -308,6 +347,10 @@ func StepOut(dbp Process) error {
 	if _, err := dbp.Valid(); err != nil {
 		return err
 	}
+	if dbp.Breakpoints().HasInternalBreakpoints() {
+		return fmt.Errorf("next while nexting")
+	}
+
 	selg := dbp.SelectedGoroutine()
 	curthread := dbp.CurrentThread()
 

pkg/proc/registers.go

@@ -23,8 +23,9 @@ type Registers interface {
 	// GAddr returns the address of the G variable if it is known, 0 and false otherwise
 	GAddr() (uint64, bool)
 	Get(int) (uint64, error)
-	SetPC(Thread, uint64) error
 	Slice() []Register
+	// Save saves a copy of this object that will survive restarts
+	Save() SavedRegisters
 }
 
 type Register struct {
@@ -33,6 +34,9 @@ type Register struct {
 	Value string
 }
 
+type SavedRegisters interface {
+}
+
 // AppendWordReg appends a word (16 bit) register to regs.
 func AppendWordReg(regs []Register, name string, value uint16) []Register {
 	var buf bytes.Buffer
@@ -266,7 +270,8 @@ type PtraceFpRegs struct {
 // Manual, Volume 1: Basic Architecture.
 type LinuxX86Xstate struct {
 	PtraceFpRegs
-	AvxState bool // contains AVX state
+	Xsave    []byte // raw xsave area
+	AvxState bool   // contains AVX state
 	YmmSpace [256]byte
 }
 

pkg/proc/threads.go

@@ -23,6 +23,8 @@ type Thread interface {
 	Breakpoint() BreakpointState
 	ThreadID() int
 	Registers(floatingPoint bool) (Registers, error)
+	// RestoreRegisters restores saved registers
+	RestoreRegisters(SavedRegisters) error
 	Arch() Arch
 	BinInfo() *BinaryInfo
 	StepInstruction() error
@@ -32,6 +34,9 @@ type Thread interface {
 	SetCurrentBreakpoint() error
 	// Common returns the CommonThread structure for this thread
 	Common() *CommonThread
+
+	SetPC(uint64) error
+	SetSP(uint64) error
 }
 
 // Location represents the location of a thread.
@@ -504,14 +509,6 @@ func GoroutineScope(thread Thread) (*EvalScope, error) {
 	return FrameToScope(thread.BinInfo(), thread, g, locations...), nil
 }
 
-func onRuntimeBreakpoint(thread Thread) bool {
-	loc, err := thread.Location()
-	if err != nil {
-		return false
-	}
-	return loc.Fn != nil && loc.Fn.Name == "runtime.breakpoint"
-}
-
 // onNextGoroutine returns true if this thread is on the goroutine requested by the current 'next' command
 func onNextGoroutine(thread Thread, breakpoints *BreakpointMap) (bool, error) {
 	var bp *Breakpoint

pkg/proc/variables.go

@@ -149,6 +149,7 @@ type G struct {
 	stkbarVar  *Variable // stkbar field of g struct
 	stkbarPos  int       // stkbarPos field of g struct
 	stackhi    uint64    // value of stack.hi
+	stacklo    uint64    // value of stack.lo
 
 	SystemStack bool // SystemStack is true if this goroutine is currently executing on a system stack.
 
@@ -364,11 +365,6 @@ func (scope *EvalScope) DwarfReader() *reader.Reader {
 	return scope.BinInfo.DwarfReader()
 }
 
-// Type returns the Dwarf type entry at `offset`.
-func (scope *EvalScope) Type(offset dwarf.Offset) (godwarf.Type, error) {
-	return godwarf.ReadType(scope.BinInfo.dwarf, offset, scope.BinInfo.typeCache)
-}
-
 // PtrSize returns the size of a pointer.
 func (scope *EvalScope) PtrSize() int {
 	return scope.BinInfo.Arch.PtrSize()
@@ -434,11 +430,14 @@ func (gvar *Variable) parseG() (*G, error) {
 		}
 
 	}
-	var stackhi uint64
+	var stackhi, stacklo uint64
 	if stackVar := gvar.fieldVariable("stack"); stackVar != nil {
 		if stackhiVar := stackVar.fieldVariable("hi"); stackhiVar != nil {
 			stackhi, _ = constant.Uint64Val(stackhiVar.Value)
 		}
+		if stackloVar := stackVar.fieldVariable("lo"); stackloVar != nil {
+			stacklo, _ = constant.Uint64Val(stackloVar.Value)
+		}
 	}
 
 	stkbarVar, _ := gvar.structMember("stkbar")
@@ -464,6 +463,7 @@ func (gvar *Variable) parseG() (*G, error) {
 		stkbarVar:  stkbarVar,
 		stkbarPos:  int(stkbarPos),
 		stackhi:    stackhi,
+		stacklo:    stacklo,
 	}
 	return g, nil
 }
@@ -715,10 +715,20 @@ func (scope *EvalScope) findGlobal(name string) (*Variable, error) {
 			return scope.extractVarInfoFromEntry(entry)
 		}
 	}
+	for _, fn := range scope.BinInfo.Functions {
+		if fn.Name == name || strings.HasSuffix(fn.Name, "/"+name) {
+			//TODO(aarzilli): convert function entry into a function type?
+			r := scope.newVariable(fn.Name, uintptr(fn.Entry), &godwarf.FuncType{}, scope.Mem)
+			r.Value = constant.MakeString(fn.Name)
+			r.Base = uintptr(fn.Entry)
+			r.loaded = true
+			return r, nil
+		}
+	}
 	for offset, ctyp := range scope.BinInfo.consts {
 		for _, cval := range ctyp.values {
 			if cval.fullName == name || strings.HasSuffix(cval.fullName, "/"+name) {
-				t, err := scope.Type(offset)
+				t, err := scope.BinInfo.Type(offset)
 				if err != nil {
 					return nil, err
 				}
@@ -809,6 +819,27 @@ func (v *Variable) structMember(memberName string) (*Variable, error) {
 	}
 }
 
+func readVarEntry(varEntry *dwarf.Entry, bi *BinaryInfo) (entry reader.Entry, name string, typ godwarf.Type, err error) {
+	entry, _ = reader.LoadAbstractOrigin(varEntry, bi.dwarfReader)
+
+	name, ok := entry.Val(dwarf.AttrName).(string)
+	if !ok {
+		return nil, "", nil, fmt.Errorf("malformed variable DIE (name)")
+	}
+
+	offset, ok := entry.Val(dwarf.AttrType).(dwarf.Offset)
+	if !ok {
+		return nil, "", nil, fmt.Errorf("malformed variable DIE (offset)")
+	}
+
+	typ, err = bi.Type(offset)
+	if err != nil {
+		return nil, "", nil, err
+	}
+
+	return entry, name, typ, nil
+}
+
 // Extracts the name and type of a variable from a dwarf entry
 // then executes the instructions given in the  DW_AT_location attribute to grab the variable's address
 func (scope *EvalScope) extractVarInfoFromEntry(varEntry *dwarf.Entry) (*Variable, error) {
@@ -820,19 +851,7 @@ func (scope *EvalScope) extractVarInfoFromEntry(varEntry *dwarf.Entry) (*Variabl
 		return nil, fmt.Errorf("invalid entry tag, only supports FormalParameter and Variable, got %s", varEntry.Tag.String())
 	}
 
-	entry, _ := reader.LoadAbstractOrigin(varEntry, scope.BinInfo.dwarfReader)
-
-	n, ok := entry.Val(dwarf.AttrName).(string)
-	if !ok {
-		return nil, fmt.Errorf("type assertion failed")
-	}
-
-	offset, ok := entry.Val(dwarf.AttrType).(dwarf.Offset)
-	if !ok {
-		return nil, fmt.Errorf("type assertion failed")
-	}
-
-	t, err := scope.Type(offset)
+	entry, n, t, err := readVarEntry(varEntry, scope.BinInfo)
 	if err != nil {
 		return nil, err
 	}
@@ -1130,6 +1149,7 @@ func (v *Variable) loadChanInfo() {
 	if sv.Unreadable != nil || sv.Addr == 0 {
 		return
 	}
+	v.Base = sv.Addr
 	structType, ok := sv.DwarfType.(*godwarf.StructType)
 	if !ok {
 		v.Unreadable = errors.New("bad channel type")

pkg/terminal/command.go

@@ -128,6 +128,24 @@ See also: "help on", "help cond" and "help clear"`},
 		{aliases: []string{"step-instruction", "si"}, cmdFn: c.stepInstruction, helpMsg: "Single step a single cpu instruction."},
 		{aliases: []string{"next", "n"}, cmdFn: c.next, helpMsg: "Step over to next source line."},
 		{aliases: []string{"stepout"}, cmdFn: c.stepout, helpMsg: "Step out of the current function."},
+		{aliases: []string{"call"}, cmdFn: c.call, helpMsg: `Resumes process, injecting a function call (EXPERIMENTAL!!!)
+	
+Current limitations:
+- can only call package-level functions, no function pointers nor methods.
+- only things that have an address can be used as arguments (no literal
+  constants or results of evaluating some expressions).
+- only pointers to stack-allocated objects can be passed as argument.
+- no automatic type conversions are supported, including automatically
+  converting to an interface type.
+- functions can only be called on running goroutines that are not
+  executing the runtime.
+- the current goroutine needs to have at least 256 bytes of free space on
+  the stack.
+- functions can only be called when the goroutine is stopped at a safe
+  point.
+- calling a function will resume execution of all goroutines.
+- only supported on linux's native backend.
+`},
 		{aliases: []string{"threads"}, cmdFn: threads, helpMsg: "Print out info for every traced thread."},
 		{aliases: []string{"thread", "tr"}, cmdFn: thread, helpMsg: `Switch to the specified thread.
 
@@ -936,6 +954,20 @@ func (c *Commands) stepout(t *Term, ctx callContext, args string) error {
 	return continueUntilCompleteNext(t, state, "stepout")
 }
 
+func (c *Commands) call(t *Term, ctx callContext, args string) error {
+	if err := scopePrefixSwitch(t, ctx); err != nil {
+		return err
+	}
+	state, err := exitedToError(t.client.Call(args))
+	c.frame = 0
+	if err != nil {
+		printfileNoState(t)
+		return err
+	}
+	printcontext(t, state)
+	return continueUntilCompleteNext(t, state, "call")
+}
+
 func clear(t *Term, ctx callContext, args string) error {
 	if len(args) == 0 {
 		return fmt.Errorf("not enough arguments")

service/api/types.go

@@ -275,6 +275,8 @@ type DebuggerCommand struct {
 	// When ReturnInfoLoadConfig is not nil it will be used to load the value
 	// of any return variables.
 	ReturnInfoLoadConfig *LoadConfig
+	// Expr is the expression argument for a Call command
+	Expr string `json:"expr,omitempty"`
 }
 
 // Informations about the current breakpoint
@@ -310,6 +312,8 @@ const (
 	SwitchGoroutine = "switchGoroutine"
 	// Halt suspends the process.
 	Halt = "halt"
+	// Call resumes process execution injecting a function call.
+	Call = "call"
 )
 
 type AssemblyFlavour int

service/client.go

@@ -38,6 +38,8 @@ type Client interface {
 	Step() (*api.DebuggerState, error)
 	// StepOut continues to the return address of the current function
 	StepOut() (*api.DebuggerState, error)
+	// Call resumes process execution while making a function call.
+	Call(expr string) (*api.DebuggerState, error)
 
 	// SingleStep will step a single cpu instruction.
 	StepInstruction() (*api.DebuggerState, error)

service/debugger/debugger.go

@@ -558,6 +558,9 @@ func (d *Debugger) Command(command *api.DebuggerCommand) (*api.DebuggerState, er
 	case api.Continue:
 		d.log.Debug("continuing")
 		err = proc.Continue(d.target)
+	case api.Call:
+		d.log.Debugf("function call %s", command.Expr)
+		err = proc.CallFunction(d.target, command.Expr, api.LoadConfigToProc(command.ReturnInfoLoadConfig))
 	case api.Rewind:
 		d.log.Debug("rewinding")
 		if err := d.target.Direction(proc.Backward); err != nil {
@@ -618,7 +621,7 @@ func (d *Debugger) collectBreakpointInformation(state *api.DebuggerState) error
 	}
 
 	for i := range state.Threads {
-		if state.Threads[i].Breakpoint == nil {
+		if state.Threads[i].Breakpoint == nil || state.Threads[i].BreakpointInfo != nil {
 			continue
 		}
 

service/rpc1/client.go

@@ -113,6 +113,12 @@ func (c *RPCClient) Step() (*api.DebuggerState, error) {
 	return state, err
 }
 
+func (c *RPCClient) Call(expr string) (*api.DebuggerState, error) {
+	state := new(api.DebuggerState)
+	err := c.call("Command", &api.DebuggerCommand{Name: api.Call, Expr: expr}, state)
+	return state, err
+}
+
 func (c *RPCClient) StepInstruction() (*api.DebuggerState, error) {
 	state := new(api.DebuggerState)
 	err := c.call("Command", &api.DebuggerCommand{Name: api.StepInstruction}, state)

service/rpc2/client.go

@@ -139,6 +139,12 @@ func (c *RPCClient) StepOut() (*api.DebuggerState, error) {
 	return &out.State, err
 }
 
+func (c *RPCClient) Call(expr string) (*api.DebuggerState, error) {
+	var out CommandOut
+	err := c.call("Command", &api.DebuggerCommand{Name: api.Call, ReturnInfoLoadConfig: c.retValLoadCfg, Expr: expr}, &out)
+	return &out.State, err
+}
+
 func (c *RPCClient) StepInstruction() (*api.DebuggerState, error) {
 	var out CommandOut
 	err := c.call("Command", api.DebuggerCommand{Name: api.StepInstruction}, &out)

service/test/integration2_test.go

@@ -17,6 +17,7 @@ import (
 	protest "github.com/derekparker/delve/pkg/proc/test"
 
 	"github.com/derekparker/delve/pkg/goversion"
+	"github.com/derekparker/delve/pkg/logflags"
 	"github.com/derekparker/delve/service"
 	"github.com/derekparker/delve/service/api"
 	"github.com/derekparker/delve/service/rpc2"
@@ -28,6 +29,8 @@ var testBackend string
 
 func TestMain(m *testing.M) {
 	flag.StringVar(&testBackend, "backend", "", "selects backend")
+	var logOutput string
+	flag.StringVar(&logOutput, "log-output", "", "configures log output")
 	flag.Parse()
 	if testBackend == "" {
 		testBackend = os.Getenv("PROCTEST")
@@ -35,6 +38,7 @@ func TestMain(m *testing.M) {
 			testBackend = "native"
 		}
 	}
+	logflags.Setup(logOutput != "", logOutput)
 	os.Exit(protest.RunTestsWithFixtures(m))
 }
 
@@ -1495,3 +1499,123 @@ func TestAcceptMulticlient(t *testing.T) {
 	client2.Detach(true)
 	<-serverDone
 }
+
+func mustHaveDebugCalls(t *testing.T, c service.Client) {
+	locs, err := c.FindLocation(api.EvalScope{-1, 0}, "runtime.debugCallV1")
+	if len(locs) == 0 || err != nil {
+		t.Skip("function calls not supported on this version of go")
+	}
+}
+
+func TestClientServerFunctionCall(t *testing.T) {
+	if runtime.GOOS != "linux" || testBackend != "native" {
+		t.Skip("unsupported")
+	}
+	withTestClient2("fncall", t, func(c service.Client) {
+		mustHaveDebugCalls(t, c)
+		c.SetReturnValuesLoadConfig(&normalLoadConfig)
+		state := <-c.Continue()
+		assertNoError(state.Err, t, "Continue()")
+		beforeCallFn := state.CurrentThread.Function.Name
+		state, err := c.Call("call1(one, two)")
+		assertNoError(err, t, "Call()")
+		t.Logf("returned to %q", state.CurrentThread.Function.Name)
+		if state.CurrentThread.Function.Name != beforeCallFn {
+			t.Fatalf("did not return to the calling function %q %q", beforeCallFn, state.CurrentThread.Function.Name)
+		}
+		if state.CurrentThread.ReturnValues == nil {
+			t.Fatal("no return values on return from call")
+		}
+		t.Logf("Return values %v", state.CurrentThread.ReturnValues)
+		if len(state.CurrentThread.ReturnValues) != 1 {
+			t.Fatal("not enough return values")
+		}
+		if state.CurrentThread.ReturnValues[0].Value != "3" {
+			t.Fatalf("wrong return value %s", state.CurrentThread.ReturnValues[0].Value)
+		}
+		state = <-c.Continue()
+		if !state.Exited {
+			t.Fatalf("expected process to exit after call %v", state.CurrentThread)
+		}
+	})
+}
+
+func TestClientServerFunctionCallBadPos(t *testing.T) {
+	if runtime.GOOS != "linux" || testBackend != "native" {
+		t.Skip("unsupported")
+	}
+	withTestClient2("fncall", t, func(c service.Client) {
+		mustHaveDebugCalls(t, c)
+		loc, err := c.FindLocation(api.EvalScope{-1, 0}, "fmt/print.go:649")
+		assertNoError(err, t, "could not find location")
+
+		_, err = c.CreateBreakpoint(&api.Breakpoint{File: loc[0].File, Line: loc[0].Line})
+		assertNoError(err, t, "CreateBreakpoin")
+
+		state := <-c.Continue()
+		assertNoError(state.Err, t, "Continue()")
+
+		state = <-c.Continue()
+		assertNoError(state.Err, t, "Continue()")
+
+		state, err = c.Call("main.call1(main.zero, main.zero)")
+		if err == nil || err.Error() != "call not at safe point" {
+			t.Fatalf("wrong error or no error: %v", err)
+		}
+	})
+}
+
+func TestClientServerFunctionCallPanic(t *testing.T) {
+	if runtime.GOOS != "linux" || testBackend != "native" {
+		t.Skip("unsupported")
+	}
+	withTestClient2("fncall", t, func(c service.Client) {
+		mustHaveDebugCalls(t, c)
+		c.SetReturnValuesLoadConfig(&normalLoadConfig)
+		state := <-c.Continue()
+		assertNoError(state.Err, t, "Continue()")
+		state, err := c.Call("callpanic()")
+		assertNoError(err, t, "Call()")
+		t.Logf("at: %s:%d", state.CurrentThread.File, state.CurrentThread.Line)
+		if state.CurrentThread.ReturnValues == nil {
+			t.Fatal("no return values on return from call")
+		}
+		t.Logf("Return values %v", state.CurrentThread.ReturnValues)
+		if len(state.CurrentThread.ReturnValues) != 1 {
+			t.Fatal("not enough return values")
+		}
+		if state.CurrentThread.ReturnValues[0].Name != "~panic" {
+			t.Fatal("not a panic")
+		}
+		if state.CurrentThread.ReturnValues[0].Children[0].Value != "callpanic panicked" {
+			t.Fatalf("wrong panic value %s", state.CurrentThread.ReturnValues[0].Children[0].Value)
+		}
+	})
+}
+
+func TestClientServerFunctionCallStacktrace(t *testing.T) {
+	if runtime.GOOS != "linux" || testBackend != "native" {
+		t.Skip("unsupported")
+	}
+	withTestClient2("fncall", t, func(c service.Client) {
+		mustHaveDebugCalls(t, c)
+		c.SetReturnValuesLoadConfig(&api.LoadConfig{false, 0, 2048, 0, 0})
+		state := <-c.Continue()
+		assertNoError(state.Err, t, "Continue()")
+		state, err := c.Call("callstacktrace()")
+		assertNoError(err, t, "Call()")
+		t.Logf("at: %s:%d", state.CurrentThread.File, state.CurrentThread.Line)
+		if state.CurrentThread.ReturnValues == nil {
+			t.Fatal("no return values on return from call")
+		}
+		if len(state.CurrentThread.ReturnValues) != 1 || state.CurrentThread.ReturnValues[0].Kind != reflect.String {
+			t.Fatal("not enough return values")
+		}
+		st := state.CurrentThread.ReturnValues[0].Value
+		t.Logf("Returned stacktrace:\n%s", st)
+
+		if !strings.Contains(st, "main.callstacktrace") || !strings.Contains(st, "main.main") || !strings.Contains(st, "runtime.main") {
+			t.Fatal("bad stacktrace returned")
+		}
+	})
+}

service/test/variables_test.go

@@ -739,6 +739,9 @@ func TestEvalExpression(t *testing.T) {
 		// shortcircuited logical operators
 		{"nilstruct != nil && nilstruct.A == 1", false, "false", "false", "", nil},
 		{"nilstruct == nil || nilstruct.A == 1", false, "true", "true", "", nil},
+
+		{"afunc", true, `main.afunc`, `main.afunc`, `func()`, nil},
+		{"main.afunc2", true, `main.afunc2`, `main.afunc2`, `func()`, nil},
 	}
 
 	ver, _ := goversion.Parse(runtime.Version())