prog: make c.Ret optional

No reason to allocate return value if there is no return type.
c.Ret == nil is the reasonable indication that this is a "void" call.

5 files changed, 32 insertions, 20 deletions

diff --git a/prog/clone.go b/prog/clone.go
index 51d801e28..3b6ba0fbc 100644
--- a/prog/clone.go
+++ b/prog/clone.go
@@ -12,7 +12,9 @@ func (p *Prog) Clone() *Prog {
 	for ci, c := range p.Calls {
 		c1 := new(Call)
 		c1.Meta = c.Meta
-		c1.Ret = clone(c.Ret, newargs).(*ResultArg)
+		if c.Ret != nil {
+			c1.Ret = clone(c.Ret, newargs).(*ResultArg)
+		}
 		c1.Args = make([]Arg, len(c.Args))
 		for ai, arg := range c.Args {
 			c1.Args[ai] = clone(arg, newargs)
diff --git a/prog/encoding.go b/prog/encoding.go
index 86577cd12..f0d96da95 100644
--- a/prog/encoding.go
+++ b/prog/encoding.go
@@ -33,7 +33,7 @@ func (p *Prog) Serialize() []byte {
 	vars := make(map[*ResultArg]int)
 	varSeq := 0
 	for _, c := range p.Calls {
-		if len(c.Ret.uses) != 0 {
+		if c.Ret != nil && len(c.Ret.uses) != 0 {
 			fmt.Fprintf(buf, "r%v = ", varSeq)
 			vars[c.Ret] = varSeq
 			varSeq++
@@ -206,7 +206,7 @@ func (target *Target) Deserialize(data []byte) (prog *Prog, err error) {
 		if len(c.Args) != len(meta.Args) {
 			return nil, fmt.Errorf("wrong call arg count: %v, want %v", len(c.Args), len(meta.Args))
 		}
-		if r != "" {
+		if r != "" && c.Ret != nil {
 			vars[r] = c.Ret
 		}
 	}
diff --git a/prog/encodingexec.go b/prog/encodingexec.go
index 9d918b155..a162a7126 100644
--- a/prog/encodingexec.go
+++ b/prog/encodingexec.go
@@ -152,7 +152,7 @@ func (p *Prog) SerializeForExec(buffer []byte) (int, error) {
 		}
 		// Generate the call itself.
 		w.write(uint64(c.Meta.ID))
-		if len(c.Ret.uses) != 0 {
+		if c.Ret != nil && len(c.Ret.uses) != 0 {
 			if _, ok := w.args[c.Ret]; ok {
 				panic("argInfo is already created for return value")
 			}
diff --git a/prog/prog.go b/prog/prog.go
index ef09d46a9..19f5e319f 100644
--- a/prog/prog.go
+++ b/prog/prog.go
@@ -261,8 +261,10 @@ func MakeResultArg(t Type, r *ResultArg, v uint64) *ResultArg {
 }
 
 func MakeReturnArg(t Type) *ResultArg {
-	// TODO(dvyukov): we should not create return arg at all if t is nil.
-	if t != nil && t.Dir() != DirOut {
+	if t == nil {
+		return nil
+	}
+	if t.Dir() != DirOut {
 		panic("return arg is not out")
 	}
 	return &ResultArg{ArgCommon: ArgCommon{typ: t}}
@@ -491,7 +493,9 @@ func (p *Prog) removeCall(idx int) {
 	for _, arg := range c.Args {
 		removeArg(arg)
 	}
-	removeArg(c.Ret)
+	if c.Ret != nil {
+		removeArg(c.Ret)
+	}
 	copy(p.Calls[idx:], p.Calls[idx+1:])
 	p.Calls = p.Calls[:len(p.Calls)-1]
 }
diff --git a/prog/validation.go b/prog/validation.go
index f6e0780fd..ac7faeee2 100644
--- a/prog/validation.go
+++ b/prog/validation.go
@@ -47,26 +47,31 @@ func (p *Prog) validateCall(ctx *validCtx, c *Call) error {
 			return err
 		}
 	}
-	if c.Ret == nil {
-		return fmt.Errorf("syscall %v: return value is absent", c.Meta.Name)
-	}
-	if c.Ret.Type() != nil && c.Ret.Type().Dir() != DirOut {
-		return fmt.Errorf("syscall %v: return value %v is not output", c.Meta.Name, c.Ret)
-	} else if c.Ret.Res != nil || c.Ret.Val != 0 || c.Ret.OpDiv != 0 || c.Ret.OpAdd != 0 {
-		return fmt.Errorf("syscall %v: return value %v is not empty", c.Meta.Name, c.Ret)
-	}
-	if c.Meta.Ret != nil {
+	if c.Meta.Ret == nil {
+		if c.Ret != nil {
+			return fmt.Errorf("syscall %v: return value without type", c.Meta.Name)
+		}
+	} else {
+		if c.Ret == nil {
+			return fmt.Errorf("syscall %v: return value is absent", c.Meta.Name)
+		}
+		if c.Ret.Type() != c.Meta.Ret {
+			return fmt.Errorf("syscall %v: wrong return type", c.Meta.Name)
+		}
+		if c.Ret.Type().Dir() != DirOut {
+			return fmt.Errorf("syscall %v: return value %v is not output", c.Meta.Name, c.Ret)
+		}
+		if c.Ret.Res != nil || c.Ret.Val != 0 || c.Ret.OpDiv != 0 || c.Ret.OpAdd != 0 {
+			return fmt.Errorf("syscall %v: return value %v is not empty", c.Meta.Name, c.Ret)
+		}
 		if err := validateArg(ctx, c, c.Ret); err != nil {
 			return err
 		}
-	} else if c.Ret.Type() != nil {
-		return fmt.Errorf("syscall %v: return value has spurious type: %+v",
-			c.Meta.Name, c.Ret.Type())
 	}
 	return nil
 }
 
-// nolint
+// nolint: gocyclo
 func validateArg(ctx *validCtx, c *Call, arg Arg) error {
 	if arg == nil {
 		return fmt.Errorf("syscall %v: nil arg", c.Meta.Name)
@@ -76,6 +81,7 @@ func validateArg(ctx *validCtx, c *Call, arg Arg) error {
 			c.Meta.Name, arg)
 	}
 	ctx.args[arg] = true
+	// TODO(dvyukov): move this to ResultArg verification.
 	if used, ok := arg.(*ResultArg); ok {
 		for u := range used.uses {
 			if u == nil {