printer: shorten text size when argsize is zero

printer/goasm.go

@@ -1,6 +1,7 @@
 package printer
 
 import (
+	"strconv"
 	"strings"
 
 	"github.com/mmcloughlin/avo"
@@ -48,7 +49,7 @@ func (p *goasm) include(path string) {
 func (p *goasm) function(f *avo.Function) {
 	p.NL()
 	p.Comment(f.Stub())
-	p.Printf("TEXT %s%s(SB),0,$%d-%d\n", dot, f.Name, f.FrameBytes(), f.ArgumentBytes())
+	p.Printf("TEXT %s%s(SB), 0, %s\n", dot, f.Name, textsize(f))
 
 	for _, node := range f.Nodes {
 		switch n := node.(type) {
@@ -73,7 +74,24 @@ func (p *goasm) global(g *avo.Global) {
 		p.Printf("DATA %s/%d, %s\n", a.Asm(), d.Value.Bytes(), d.Value.Asm())
 	}
 	// TODO(mbm): replace hardcoded RODATA with an attributes list
-	p.Printf("GLOBL %s%s(SB), RODATA, $%d\n", dot, g.Symbol, g.Size)
+	p.Printf("GLOBL %s(SB), RODATA, $%d\n", g.Symbol, g.Size)
+}
+
+func textsize(f *avo.Function) string {
+	// Reference: https://github.com/golang/go/blob/b115207baf6c2decc3820ada4574ef4e5ad940ec/src/cmd/internal/obj/util.go#L260-L265
+	//
+	//		case TYPE_TEXTSIZE:
+	//			if a.Val.(int32) == objabi.ArgsSizeUnknown {
+	//				str = fmt.Sprintf("$%d", a.Offset)
+	//			} else {
+	//				str = fmt.Sprintf("$%d-%d", a.Offset, a.Val.(int32))
+	//			}
+	//
+	s := "$" + strconv.Itoa(f.FrameBytes())
+	if argsize := f.ArgumentBytes(); argsize > 0 {
+		return s + "-" + strconv.Itoa(argsize)
+	}
+	return s
 }
 
 func joinOperands(operands []operand.Op) string {

printer/goasm_test.go

@@ -0,0 +1,63 @@
+package printer_test
+
+import (
+	"testing"
+
+	"github.com/mmcloughlin/avo/build"
+	"github.com/mmcloughlin/avo/printer"
+	"github.com/mmcloughlin/avo/reg"
+)
+
+func TestBasic(t *testing.T) {
+	ctx := build.NewContext()
+	ctx.Function("add")
+	ctx.SignatureExpr("func(x, y uint64) uint64")
+	x := ctx.Load(ctx.Param("x"), reg.RAX)
+	y := ctx.Load(ctx.Param("y"), reg.R9)
+	ctx.ADDQ(x, y)
+	ctx.Store(y, ctx.ReturnIndex(0))
+	ctx.RET()
+
+	AssertPrintsLines(t, ctx, printer.NewGoAsm, []string{
+		"// Code generated by avo. DO NOT EDIT.",
+		"",
+		"#include \"textflag.h\"",
+		"",
+		"// func add(x uint64, y uint64) uint64",
+		"TEXT ·add(SB), 0, $0-24",
+		"\tMOVQ\tx(FP), AX",
+		"\tMOVQ\ty+8(FP), R9",
+		"\tADDQ\tAX, R9",
+		"\tMOVQ\tR9, ret+16(FP)",
+		"\tRET",
+		"",
+	})
+}
+
+func TestTextSize(t *testing.T) {
+	ctx := build.NewContext()
+
+	ctx.Function("noargs")
+	ctx.SignatureExpr("func()")
+	ctx.AllocLocal(16)
+	ctx.RET()
+
+	ctx.Function("withargs")
+	ctx.SignatureExpr("func(x, y uint64) uint64")
+	ctx.RET()
+
+	AssertPrintsLines(t, ctx, printer.NewGoAsm, []string{
+		"// Code generated by avo. DO NOT EDIT.",
+		"",
+		"#include \"textflag.h\"",
+		"",
+		"// func noargs()",
+		"TEXT ·noargs(SB), 0, $16", // expect only the frame size
+		"\tRET",
+		"",
+		"// func withargs(x uint64, y uint64) uint64",
+		"TEXT ·withargs(SB), 0, $0-24", // expect both frame size and argument size
+		"\tRET",
+		"",
+	})
+}

printer/util_test.go

@@ -0,0 +1,43 @@
+package printer_test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/mmcloughlin/avo/build"
+	"github.com/mmcloughlin/avo/printer"
+)
+
+func AssertPrintsLines(t *testing.T, ctx *build.Context, pb printer.Builder, expect []string) {
+	t.Helper()
+
+	output := Print(t, ctx, pb)
+	lines := strings.Split(output, "\n")
+
+	if len(expect) != len(lines) {
+		t.Fatalf("have %d lines of output; expected %d", len(lines), len(expect))
+	}
+
+	for i := range expect {
+		if expect[i] != lines[i] {
+			t.Errorf("mismatch on line %d:\n\tgot\t%s\n\texpect\t%s\n", i, lines[i], expect[i])
+		}
+	}
+}
+
+func Print(t *testing.T, ctx *build.Context, pb printer.Builder) string {
+	t.Helper()
+
+	f, errs := ctx.Result()
+	if errs != nil {
+		t.Fatal(errs)
+	}
+
+	p := pb(printer.NewDefaultConfig())
+	b, err := p.Print(f)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return string(b)
+}