loader/cgo: add support for function pointers

Author: aykevl

compiler/compiler.go

@@ -2990,6 +2990,16 @@ func (c *Compiler) parseUnOp(frame *Frame, unop *ssa.UnOp) (llvm.Value, error) {
 		if c.targetData.TypeAllocSize(x.Type().ElementType()) == 0 {
 			// zero-length data
 			return c.getZeroValue(x.Type().ElementType())
+		} else if strings.HasSuffix(unop.X.String(), "$funcaddr") {
+			// CGo function pointer. The cgo part has rewritten CGo function
+			// pointers as stub global variables of the form:
+			//     var C.add unsafe.Pointer
+			// Instead of a load from the global, create a bitcast of the
+			// function pointer itself.
+			global := c.ir.GetGlobal(unop.X.(*ssa.Global))
+			name := global.LinkName()[:len(global.LinkName())-len("$funcaddr")]
+			fn := c.mod.NamedFunction(name)
+			return c.builder.CreateBitCast(fn, c.i8ptrType, ""), nil
 		} else {
 			load := c.builder.CreateLoad(x, "")
 			if c.ir.IsVolatile(valType) {

ir/ir.go

@@ -269,10 +269,16 @@ func (f *Function) parsePragmas() {
 	}
 	if decl, ok := f.Syntax().(*ast.FuncDecl); ok && decl.Doc != nil {
 		for _, comment := range decl.Doc.List {
-			if !strings.HasPrefix(comment.Text, "//go:") {
+			text := comment.Text
+			if strings.HasPrefix(text, "//export ") {
+				// Rewrite '//export' to '//go:export' for compatibility with
+				// gc.
+				text = "//go:" + text[2:]
+			}
+			if !strings.HasPrefix(text, "//go:") {
 				continue
 			}
-			parts := strings.Fields(comment.Text)
+			parts := strings.Fields(text)
 			switch parts[0] {
 			case "//go:export":
 				if len(parts) != 2 {
@@ -322,15 +328,15 @@ func (f *Function) IsNoBounds() bool {
 
 // Return true iff this function is externally visible.
 func (f *Function) IsExported() bool {
-	return f.exported
+	return f.exported || f.CName() != ""
 }
 
 // Return true for functions annotated with //go:interrupt. The function name is
 // already customized in LinkName() to hook up in the interrupt vector.
 //
 // On some platforms (like AVR), interrupts need a special compiler flag.
 func (f *Function) IsInterrupt() bool {
-	return f.exported
+	return f.interrupt
 }
 
 // Return the link name for this function.

loader/cgo.go

@@ -130,6 +130,9 @@ func (p *Package) processCgo(filename string, f *ast.File, cflags []string) erro
 	// Declare functions found by libclang.
 	info.addFuncDecls()
 
+	// Declare stub function pointer values found by libclang.
+	info.addFuncPtrDecls()
+
 	// Declare globals found by libclang.
 	info.addVarDecls()
 
@@ -199,6 +202,55 @@ func (info *fileInfo) addFuncDecls() {
 	}
 }
 
+// addFuncPtrDecls creates stub declarations of function pointer values. These
+// values will later be replaced with the real values in the compiler.
+// It adds code like the following to the AST:
+//
+//     var (
+//         C.add unsafe.Pointer
+//         C.mul unsafe.Pointer
+//         // ...
+//     )
+func (info *fileInfo) addFuncPtrDecls() {
+	gen := &ast.GenDecl{
+		TokPos: info.importCPos,
+		Tok:    token.VAR,
+		Lparen: info.importCPos,
+		Rparen: info.importCPos,
+	}
+	names := make([]string, 0, len(info.functions))
+	for name := range info.functions {
+		names = append(names, name)
+	}
+	sort.Strings(names)
+	for _, name := range names {
+		obj := &ast.Object{
+			Kind: ast.Typ,
+			Name: "C." + name + "$funcaddr",
+		}
+		valueSpec := &ast.ValueSpec{
+			Names: []*ast.Ident{&ast.Ident{
+				NamePos: info.importCPos,
+				Name:    "C." + name + "$funcaddr",
+				Obj:     obj,
+			}},
+			Type: &ast.SelectorExpr{
+				X: &ast.Ident{
+					NamePos: info.importCPos,
+					Name:    "unsafe",
+				},
+				Sel: &ast.Ident{
+					NamePos: info.importCPos,
+					Name:    "Pointer",
+				},
+			},
+		}
+		obj.Decl = valueSpec
+		gen.Specs = append(gen.Specs, valueSpec)
+	}
+	info.Decls = append(info.Decls, gen)
+}
+
 // addVarDecls declares external C globals in the Go source.
 // It adds code like the following to the AST:
 //
@@ -327,15 +379,34 @@ func (info *fileInfo) addTypedefs() {
 // separate namespace (no _Cgo_ hacks like in gc).
 func (info *fileInfo) walker(cursor *astutil.Cursor) bool {
 	switch node := cursor.Node().(type) {
+	case *ast.CallExpr:
+		fun, ok := node.Fun.(*ast.SelectorExpr)
+		if !ok {
+			return true
+		}
+		x, ok := fun.X.(*ast.Ident)
+		if !ok {
+			return true
+		}
+		if _, ok := info.functions[fun.Sel.Name]; ok && x.Name == "C" {
+			node.Fun = &ast.Ident{
+				NamePos: x.NamePos,
+				Name:    "C." + fun.Sel.Name,
+			}
+		}
 	case *ast.SelectorExpr:
 		x, ok := node.X.(*ast.Ident)
 		if !ok {
 			return true
 		}
 		if x.Name == "C" {
+			name := "C." + node.Sel.Name
+			if _, ok := info.functions[node.Sel.Name]; ok {
+				name += "$funcaddr"
+			}
 			cursor.Replace(&ast.Ident{
 				NamePos: x.NamePos,
-				Name:    "C." + node.Sel.Name,
+				Name:    name,
 			})
 		}
 	}

loader/libclang.go

@@ -6,6 +6,8 @@ package loader
 import (
 	"errors"
 	"go/ast"
+	"go/token"
+	"strconv"
 	"strings"
 	"unsafe"
 )
@@ -90,13 +92,16 @@ func tinygo_clang_visitor(c, parent C.CXCursor, client_data C.CXClientData) C.in
 		if C.clang_isFunctionTypeVariadic(cursorType) != 0 {
 			return C.CXChildVisit_Continue // not supported
 		}
-		numArgs := C.clang_Cursor_getNumArguments(c)
+		numArgs := int(C.clang_Cursor_getNumArguments(c))
 		fn := &functionInfo{}
 		info.functions[name] = fn
-		for i := C.int(0); i < numArgs; i++ {
+		for i := 0; i < numArgs; i++ {
 			arg := C.clang_Cursor_getArgument(c, C.uint(i))
 			argName := getString(C.clang_getCursorSpelling(arg))
 			argType := C.clang_getArgType(cursorType, C.uint(i))
+			if argName == "" {
+				argName = "$" + strconv.Itoa(i)
+			}
 			fn.args = append(fn.args, paramInfo{
 				name:     argName,
 				typeExpr: info.makeASTType(argType),
@@ -196,6 +201,23 @@ func (info *fileInfo) makeASTType(typ C.CXType) ast.Expr {
 			Star: info.importCPos,
 			X:    info.makeASTType(C.clang_getPointeeType(typ)),
 		}
+	case C.CXType_FunctionProto:
+		// Be compatible with gc, which uses the *[0]byte type for function
+		// pointer types.
+		// Return type [0]byte because this is a function type, not a pointer to
+		// this function type.
+		return &ast.ArrayType{
+			Lbrack: info.importCPos,
+			Len: &ast.BasicLit{
+				ValuePos: info.importCPos,
+				Kind:     token.INT,
+				Value:    "0",
+			},
+			Elt: &ast.Ident{
+				NamePos: info.importCPos,
+				Name:    "byte",
+			},
+		}
 	default:
 		// Fallback, probably incorrect but at least the error points to an odd
 		// type name.

testdata/cgo/main.c

@@ -10,6 +10,10 @@ int add(int a, int b) {
 	return a + b;
 }
 
+int doCallback(int a, int b, binop_t callback) {
+	return callback(a, b);
+}
+
 void store(int value, int *ptr) {
 	*ptr = value;
 }

testdata/cgo/main.go

@@ -3,6 +3,7 @@ package main
 /*
 int fortytwo(void);
 #include "main.h"
+int mul(int, int);
 */
 import "C"
 
@@ -23,4 +24,13 @@ func main() {
 	println("15:", *ptr)
 	C.store(25, &n)
 	println("25:", *ptr)
+	cb := C.binop_t(C.add)
+	println("callback 1:", C.doCallback(20, 30, cb))
+	cb = C.binop_t(C.mul)
+	println("callback 2:", C.doCallback(20, 30, cb))
+}
+
+//export mul
+func mul(a, b C.int) C.int {
+	return a * b
 }

testdata/cgo/main.h

@@ -1,5 +1,7 @@
 typedef short myint;
 int add(int a, int b);
+typedef int (*binop_t) (int, int);
+int doCallback(int a, int b, binop_t cb);
 typedef int * intPointer;
 extern int global;
 void store(int value, int *ptr);

testdata/cgo/out.txt

@@ -6,3 +6,5 @@ longlong: -1099511627776
 global: 3
 15: 15
 25: 25
+callback 1: 50
+callback 2: 600