build,ir,printer: add InternalFunction

build/context.go

@@ -90,6 +90,12 @@ func (c *Context) Function(name string) {
 	c.file.AddSection(c.function)
 }
 
+// InternalFunction starts building a new internal function (not linked to any package) with the given name.
+func (c *Context) InternalFunction(name string) {
+	c.function = ir.NewInternalFunction(name)
+	c.file.AddSection(c.function)
+}
+
 // Doc sets documentation comment lines for the currently active function.
 func (c *Context) Doc(lines ...string) {
 	c.activefunc().Doc = lines
@@ -112,6 +118,11 @@ func (c *Context) Signature(s *gotypes.Signature) {
 
 // SignatureExpr parses the signature expression and sets it as the active function's signature.
 func (c *Context) SignatureExpr(expr string) {
+	if c.activefunc().IsInternal {
+		e := fmt.Sprintf("cannot link SignatureExpr \"%s\" with InternalFunction \"%s\"", expr, c.activefunc().Name)
+		c.adderror(errors.New(e))
+		return
+	}
 	s, err := gotypes.ParseSignatureInPackage(c.types(), expr)
 	if err != nil {
 		c.adderror(err)

build/global.go

@@ -127,6 +127,9 @@ func Dereference(ptr gotypes.Component) gotypes.Component { return ctx.Dereferen
 // Function starts building a new function with the given name.
 func Function(name string) { ctx.Function(name) }
 
+// InternalFunction starts building a new internal function (not linked to any package) with the given name.
+func InternalFunction(name string) { ctx.InternalFunction(name) }
+
 // Doc sets documentation comment lines for the currently active function.
 func Doc(lines ...string) { ctx.Doc(lines...) }
 

ir/ir.go

@@ -176,6 +176,7 @@ type Function struct {
 	Doc        []string
 	Signature  *gotypes.Signature
 	LocalSize  int
+	IsInternal bool
 
 	Nodes []Node
 
@@ -195,10 +196,20 @@ func (f *Function) section() {}
 func NewFunction(name string) *Function {
 	return &Function{
 		Name:      name,
+		IsInternal: false,
 		Signature: gotypes.NewSignatureVoid(),
 	}
 }
 
+// NewInternalFunction builds an empty internal function (not linked to any package) of the given name.
+func NewInternalFunction(name string) *Function {
+	return &Function{
+		Name:       name,
+		IsInternal: true,
+		Signature:  gotypes.NewSignatureVoid(),
+	}
+}
+
 // AddPragma adds a pragma to this function.
 func (f *Function) AddPragma(directive string, args ...string) {
 	f.Pragmas = append(f.Pragmas, Pragma{

ir/ir_test.go

@@ -24,6 +24,20 @@ func TestFunctionLabels(t *testing.T) {
 	}
 }
 
+func TestIsNotInternal(t *testing.T) {
+	f := NewFunction("isNotInternal")
+	if f.IsInternal {
+		t.Fatalf("expected f.IsInternal to be false, got %t", f.IsInternal)
+	}
+}
+
+func TestIsInternal(t *testing.T) {
+	f := NewInternalFunction("isInternal")
+	if !f.IsInternal {
+		t.Fatalf("expected f.IsInternal to be true, got %t", f.IsInternal)
+	}
+}
+
 func TestInputRegisters(t *testing.T) {
 	cases := []struct {
 		Name   string

printer/goasm.go

@@ -67,12 +67,22 @@ func (p *goasm) includes(paths []string) {
 
 func (p *goasm) function(f *ir.Function) {
 	p.NL()
-	p.Comment(f.Stub())
+	if !f.IsInternal {
+		p.Comment(f.Stub())
+	} else {
+		p.Comment("Internal Function (not linked to any package)")
+	}
 
 	if len(f.ISA) > 0 {
 		p.Comment("Requires: " + strings.Join(f.ISA, ", "))
 	}
 
+	if f.IsInternal {
+		p.Printf("TEXT %s(SB)", f.Name)
+	} else {
+		p.Printf("TEXT %s%s(SB)", dot, f.Name)
+	}
+
 	// Reference: https://github.com/golang/go/blob/b115207baf6c2decc3820ada4574ef4e5ad940ec/src/cmd/internal/obj/util.go#L166-L176
 	//
 	//		if p.As == ATEXT {
@@ -87,7 +97,6 @@ func (p *goasm) function(f *ir.Function) {
 	//			}
 	//		}
 	//
-	p.Printf("TEXT %s%s(SB)", dot, f.Name)
 	if f.Attributes != 0 {
 		p.Printf(", %s", f.Attributes.Asm())
 	}

printer/goasm_test.go

@@ -1,6 +1,8 @@
 package printer_test
 
 import (
+	"errors"
+	"strings"
 	"testing"
 
 	"github.com/mmcloughlin/avo/attr"
@@ -34,6 +36,43 @@ func TestBasic(t *testing.T) {
 	})
 }
 
+func TestInternal(t *testing.T) {
+	ctx := build.NewContext()
+	ctx.InternalFunction("internal")
+	ctx.AllocLocal(16)
+	ctx.RET()
+
+	AssertPrintsLines(t, ctx, printer.NewGoAsm, []string{
+		"// Code generated by avo. DO NOT EDIT.",
+		"",
+		"// Internal Function (not linked to any package)",
+		"TEXT internal(SB), $16",
+		"\tRET",
+		"",
+	})
+}
+
+func TestInternalSigExp(t *testing.T) {
+	ctx := build.NewContext()
+	ctx.InternalFunction("internal")
+	ctx.SignatureExpr("invalidSig(b bool)")
+	ctx.ADDQ(reg.EAX, reg.ECX)
+
+	_, err := ctx.Result()
+	expect := "cannot link SignatureExpr \"invalidSig(b bool)\" with InternalFunction \"internal\""
+
+	var list build.ErrorList
+	if errors.As(err, &list) {
+		for _, e := range list {
+			if strings.Contains(e.Error(), expect) {
+				return
+			}
+		}
+	}
+
+	t.Fatal("Calling SignatureExpr() while the current function is an InternalFunction should generate an error")
+}
+
 func TestTextDecl(t *testing.T) {
 	ctx := build.NewContext()