Move error handling to C code

cmd/mkcgo/generate.go

@@ -19,23 +19,13 @@ func generateGo(src *mkcgo.Source, w io.Writer) {
 	// This block outputs C header includes and forward declarations for loader functions.
 	fmt.Fprintf(w, "/*\n")
 	fmt.Fprintf(w, "#cgo CFLAGS: -Wno-attributes\n\n")
-	if *includeHeader != "" {
-		fmt.Fprintf(w, "#include \"%s\"\n", *includeHeader)
-	}
 	for _, file := range src.Files {
 		fmt.Fprintf(w, "#include %q\n", file)
 	}
-	fmt.Fprintf(w, "\n")
-	for _, tag := range src.Tags() {
-		fmt.Fprintf(w, "void __mkcgoLoad_%s(void* handle);\n", tag)
-		fmt.Fprintf(w, "void __mkcgoUnload_%s();\n", tag)
-	}
-	fmt.Fprintf(w, "\n")
-	for _, fn := range src.Funcs {
-		if fn.Optional {
-			fmt.Fprintf(w, "int %s_Available();\n", fn.ImportName)
-		}
+	if *includeHeader != "" {
+		fmt.Fprintf(w, "#include \"%s\"\n", *includeHeader)
 	}
+	fmt.Fprintf(w, "#include \"%s\"\n", autogeneratedFileName(".h"))
 	fmt.Fprintf(w, "*/\n")
 	fmt.Fprintf(w, "import \"C\"\n")
 	fmt.Fprintf(w, "import \"unsafe\"\n\n")
@@ -56,10 +46,14 @@ func generateGo(src *mkcgo.Source, w io.Writer) {
 		fmt.Fprintf(w, "}\n\n")
 	}
 
-	typedefs := make(map[string]string, len(src.TypeDefs))
-	for _, def := range src.TypeDefs {
-		typedefs[def.Name] = def.Type
-	}
+	// Generate error wrapper noescape function, which hides the
+	// error state pointer from the Go garbage collector.
+	// An instance of https://github.com/golang/go/blob/d704ef76068eb7da15520b08dc7df98f45f85ffa/src/runtime/stubs.go#L194-L201
+	fmt.Fprintf(w, "//go:nosplit\n")
+	fmt.Fprintf(w, "func %s(p *C.%s) *C.%s {\n", mkcgoNoEscape, mkcgoErrState, mkcgoErrState)
+	fmt.Fprintf(w, "\tx := uintptr(unsafe.Pointer(p))\n")
+	fmt.Fprintf(w, "\treturn (*C.%s)(unsafe.Pointer(x ^ 0))\n", mkcgoErrState)
+	fmt.Fprintf(w, "}\n\n")
 
 	// Generate function wrappers.
 	for _, fn := range src.Funcs {
@@ -73,7 +67,7 @@ func generateGo(src *mkcgo.Source, w io.Writer) {
 			fmt.Fprintf(w, "\treturn C.%s_Available() != 0\n", fn.ImportName)
 			fmt.Fprintf(w, "}\n\n")
 		}
-		generateGoFn(typedefs, fn, w)
+		generateGoFn(fn, w)
 	}
 }
 
@@ -87,11 +81,15 @@ func generateGo124(src *mkcgo.Source, w io.Writer) {
 	// This block outputs C header includes and forward declarations for loader functions.
 	fmt.Fprintf(w, "/*\n")
 	for _, fn := range src.Funcs {
+		name := fn.CName
+		if fnNeedErrWrapper(fn) {
+			name = fnCErrWrapperName(fn)
+		}
 		if fn.NoEscape {
-			fmt.Fprintf(w, "#cgo noescape %s\n", fn.CName)
+			fmt.Fprintf(w, "#cgo noescape %s\n", name)
 		}
 		if fn.NoCallback {
-			fmt.Fprintf(w, "#cgo nocallback %s\n", fn.CName)
+			fmt.Fprintf(w, "#cgo nocallback %s\n", name)
 		}
 	}
 	fmt.Fprintf(w, "*/\n")
@@ -148,20 +146,71 @@ func generateGoAliases(funcs []*mkcgo.Func, w io.Writer) {
 	}
 }
 
-// generateC creates the C source file content.
-func generateC(src *mkcgo.Source, w io.Writer) {
+// generateCHeader generates C header file content with
+// the C functions defined in the autogenerated C source file.
+func generateCHeader(src *mkcgo.Source, w io.Writer) {
 	// Header and includes.
 	fmt.Fprintf(w, "// Code generated by mkcgo. DO NOT EDIT.\n\n")
+
+	fmt.Fprintf(w, "#ifndef MKCGO_H // only include this header once\n")
+	fmt.Fprintf(w, "#define MKCGO_H\n\n")
+
+	for _, file := range src.Files {
+		fmt.Fprintf(w, "#include %q\n", file)
+	}
 	if *includeHeader != "" {
 		fmt.Fprintf(w, "#include \"%s\"\n", *includeHeader)
 	}
-	for _, file := range src.Files {
-		fmt.Fprintf(w, "#include %q\n", file)
+	fmt.Fprintf(w, "\n")
+
+	// Custom types
+	fmt.Fprintf(w, "typedef void* %s;\n", mkcgoErrState)
+	fmt.Fprintf(w, "%s mkcgo_err_retrieve();\n", mkcgoErrState)
+	fmt.Fprintf(w, "void mkcgo_err_free(%s);\n", mkcgoErrState)
+	fmt.Fprintf(w, "void mkcgo_err_clear();\n\n")
+
+	// Add forward declarations for loader functions.
+	for _, tag := range src.Tags() {
+		fmt.Fprintf(w, "void __mkcgoLoad_%s(void* handle);\n", tag)
+		fmt.Fprintf(w, "void __mkcgoUnload_%s();\n", tag)
+	}
+	fmt.Fprintf(w, "\n")
+
+	// Add forward declarations for optional functions.
+	for _, fn := range src.Funcs {
+		if fn.Optional {
+			fmt.Fprintf(w, "int %s_Available();\n", fn.ImportName)
+		}
+	}
+	fmt.Fprintf(w, "\n")
+
+	// Add forward declarations for function wrappers returning errors.
+	for _, fn := range src.Funcs {
+		if !fnNeedErrWrapper(fn) {
+			continue
+		}
+		fmt.Fprintf(w, "%s %s(%s);\n", fn.Ret.Type, fnCErrWrapperName(fn), fnCErrWrapperParams(fn, false))
 	}
+	fmt.Fprintf(w, "\n")
+	fmt.Fprintf(w, "#endif // MKCGO_H\n")
+}
+
+// generateC creates the C source file content.
+func generateC(src *mkcgo.Source, w io.Writer) {
+	// Header and includes.
+	fmt.Fprintf(w, "// Code generated by mkcgo. DO NOT EDIT.\n\n")
+
 	fmt.Fprintf(w, "#include <stddef.h>\n")
 	fmt.Fprintf(w, "#include <stdlib.h>\n")
 	fmt.Fprintf(w, "#include <stdint.h>\n")
 	fmt.Fprintf(w, "#include <stdio.h>\n")
+	for _, file := range src.Files {
+		fmt.Fprintf(w, "#include %q\n", file)
+	}
+	if *includeHeader != "" {
+		fmt.Fprintf(w, "#include \"%s\"\n", *includeHeader)
+	}
+	fmt.Fprintf(w, "#include \"%s\"\n", autogeneratedFileName(".h"))
 	fmt.Fprintf(w, "\n")
 
 	// Platform-specific includes.
@@ -238,6 +287,10 @@ func generateC(src *mkcgo.Source, w io.Writer) {
 	}
 
 	// Generate C function wrappers.
+	typedefs := make(map[string]string, len(src.TypeDefs))
+	for _, def := range src.TypeDefs {
+		typedefs[def.Name] = def.Type
+	}
 	for _, fn := range src.Funcs {
 		if fn.Variadic() {
 			// cgo doesn't support variadic functions
@@ -250,11 +303,12 @@ func generateC(src *mkcgo.Source, w io.Writer) {
 			fmt.Fprintf(w, "}\n\n")
 		}
 		generateCFn(fn, w)
+		generateCFnErrorWrapper(typedefs, fn, w)
 	}
 }
 
 // generateGoFn generates Go function f.
-func generateGoFn(typedefs map[string]string, fn *mkcgo.Func, w io.Writer) {
+func generateGoFn(fn *mkcgo.Func, w io.Writer) {
 	fnCall := fmt.Sprintf("C.%s(%s)", fn.CName, fnToGoArgs(fn))
 	// Function definition
 	fmt.Fprintf(w, "func %s(%s)", fn.GoName, fnToGoParams(fn))
@@ -296,21 +350,13 @@ func generateGoFn(typedefs map[string]string, fn *mkcgo.Func, w io.Writer) {
 		fmt.Fprintf(w, "}\n\n")
 		return
 	}
-	fmt.Fprintf(w, "\t_ret := C.%s(%s)\n", fn.CName, fnToGoArgs(fn))
-
-	// Error handling
-	errCond := "<= 0"
-	if fn.ErrCond != "" {
-		errCond = fn.ErrCond
-	} else if strings.Contains(goType, "unsafe.Pointer") {
-		errCond = "== nil"
-	} else if typ, ok := typedefs[goType]; ok && typ == "void*" {
-		errCond = "== nil"
+	fmt.Fprintf(w, "\tvar _err C.%s\n", mkcgoErrState)
+	fmt.Fprintf(w, "\t_ret := C.%s(", fnCErrWrapperName(fn))
+	args := fnToGoArgs(fn)
+	if len(args) > 0 {
+		args += ", "
 	}
-	fmt.Fprintf(w, "\tvar _err error\n")
-	fmt.Fprintf(w, "\tif _ret %s {\n", errCond)
-	fmt.Fprintf(w, "\t\t_err = newOpenSSLError(\"%s\")\n", fn.CName)
-	fmt.Fprintf(w, "\t}\n")
+	fmt.Fprintf(w, "%s%s(&_err))\n", args, mkcgoNoEscape)
 
 	// Return the value
 	fmt.Fprintf(w, "\treturn ")
@@ -322,16 +368,38 @@ func generateGoFn(typedefs map[string]string, fn *mkcgo.Func, w io.Writer) {
 	} else {
 		fmt.Fprintf(w, "_ret")
 	}
-	fmt.Fprintf(w, ", _err\n")
+	fmt.Fprintf(w, ", newMkcgoErr(%q, _err)\n", fn.CName)
 	fmt.Fprintf(w, "}\n\n")
 }
 
 func generateCFn(fn *mkcgo.Func, w io.Writer) {
-	fmt.Fprintf(w, "%s %s(%s) {\n\t", fn.Ret.Type, fn.CName, fnToCArgs(fn, true))
+	fmt.Fprintf(w, "%s %s(%s) {\n\t", fn.Ret.Type, fn.CName, fnToCArgs(fn, true, true))
 	if !retIsVoid(fn.Ret) {
 		fmt.Fprintf(w, "return ")
 	}
-	fmt.Fprintf(w, "_g_%s(%s);\n", fn.ImportName, fnToCArgs(fn, false))
+	fmt.Fprintf(w, "_g_%s(%s);\n", fn.ImportName, fnToCArgs(fn, false, true))
+	fmt.Fprintf(w, "}\n\n")
+}
+
+// generateCFnErrorWrapper generates C function wrapper for function f
+// that returns an error state.
+func generateCFnErrorWrapper(typedefs map[string]string, fn *mkcgo.Func, w io.Writer) {
+	if !fnNeedErrWrapper(fn) {
+		return
+	}
+	fmt.Fprintf(w, "%s %s(%s) {\n", fn.Ret.Type, fnCErrWrapperName(fn), fnCErrWrapperParams(fn, true))
+	fmt.Fprintf(w, "\tmkcgo_err_clear();\n") // clear any previous error
+	fmt.Fprintf(w, "\t%s _ret = _g_%s(%s);\n", fn.Ret.Type, fn.ImportName, fnToCArgs(fn, false, true))
+	errCond := "<= 0"
+	if fn.ErrCond != "" {
+		errCond = fn.ErrCond
+	} else if strings.Contains(fn.Ret.Type, "*") {
+		errCond = "== NULL"
+	} else if typ, ok := typedefs[fn.Ret.Type]; ok && typ == "void*" {
+		errCond = "== NULL"
+	}
+	fmt.Fprintf(w, "\tif (_ret %s) *_err_state = mkcgo_err_retrieve();\n", errCond)
+	fmt.Fprintf(w, "\treturn _ret;\n")
 	fmt.Fprintf(w, "}\n\n")
 }
 
@@ -436,12 +504,15 @@ func cTypeToGo(t string, cgo bool) (string, bool) {
 }
 
 // paramToC returns C source code of parameter p.
-func paramToC(i int, p *mkcgo.Param, addType bool) string {
+func paramToC(i int, p *mkcgo.Param, addType, addName bool) string {
+	if p.Type == "..." {
+		return ""
+	}
 	var s string
 	if addType {
 		s += p.Type
 	}
-	if p.Type != "void" && p.Type != "..." {
+	if addName && p.Type != "void" {
 		if len(s) > 0 {
 			s += " "
 		}
@@ -470,9 +541,9 @@ func fnToGoArgs(fn *mkcgo.Func) string {
 }
 
 // fnToCArgs returns source code for C parameters for function f.
-func fnToCArgs(fn *mkcgo.Func, addType bool) string {
+func fnToCArgs(fn *mkcgo.Func, addType, addName bool) string {
 	return join(fn.Params, func(i int, p *mkcgo.Param) string {
-		return paramToC(i, p, addType)
+		return paramToC(i, p, addType, addName)
 	}, ", ")
 }
 
@@ -492,3 +563,34 @@ func join(ps []*mkcgo.Param, fn func(int, *mkcgo.Param) string, sep string) stri
 	}
 	return strings.Join(params, sep)
 }
+
+const mkcgoNoEscape = "mkcgoNoEscape"
+const mkcgoErrState = "mkcgo_err_state"
+
+// fnCErrWrapperParams returns source code for C parameters for function f
+// with the error state added as the last parameter.
+func fnCErrWrapperParams(fn *mkcgo.Func, addName bool) string {
+	errArg := mkcgoErrState + " *"
+	if addName {
+		errArg += "_err_state"
+	}
+	args := fnToCArgs(fn, true, addName)
+	if len(args) == 0 {
+		args = errArg
+	} else if args == "void" {
+		args = errArg
+	} else {
+		args += ", " + errArg
+	}
+	return args
+}
+
+// fnCErrWrapperName returns the name of the error wrapper function for function f.
+func fnCErrWrapperName(fn *mkcgo.Func) string {
+	return "_mkcgo_err_" + fn.CName
+}
+
+// fnNeedErrWrapper reports whether function fn needs an error wrapper.
+func fnNeedErrWrapper(fn *mkcgo.Func) bool {
+	return !fn.NoError && !retIsVoid(fn.Ret)
+}

cmd/mkcgo/main.go

@@ -40,45 +40,53 @@ func main() {
 		log.Fatal(err)
 	}
 
-	var gobuf, go124buf, cbuf bytes.Buffer
+	var gobuf, go124buf, hbuf, cbuf bytes.Buffer
 	generateGo(src, &gobuf)
 	generateGo124(src, &go124buf)
+	generateCHeader(src, &hbuf)
 	generateC(src, &cbuf)
 
 	// Format the generated Go source code.
 	godata := goformat(gobuf.Bytes())
 	go124data := goformat(go124buf.Bytes())
 
-	var baseName string
-	if *fileName == "" {
-		baseName = "mkcgo"
-	} else {
-		baseName = strings.TrimSuffix(*fileName, ".go")
-	}
-
 	for _, d := range []struct {
-		name string
-		data []byte
+		suffix string
+		data   []byte
 	}{
-		{baseName + ".go", godata},
-		{baseName + "_go124.go", go124data},
-		{baseName + ".c", cbuf.Bytes()},
+		{".go", godata},
+		{"_go124.go", go124data},
+		{".h", hbuf.Bytes()},
+		{".c", cbuf.Bytes()},
 	} {
+		name := autogeneratedFileName(d.suffix)
 		var err error
 		if *fileName == "" {
 			// Write output. If no explicit output file is specified,
 			// // write both Go and C output to stdout.
-			os.Stdout.WriteString("// === " + d.name + " ===\n\n")
+			os.Stdout.WriteString("// === " + name + " ===\n\n")
 			_, err = os.Stdout.Write(d.data)
 		} else {
-			err = os.WriteFile(d.name, d.data, 0o644)
+			err = os.WriteFile(name, d.data, 0o644)
 		}
 		if err != nil {
 			log.Fatal(err)
 		}
 	}
 }
 
+// autogeneratedFileName returns the name of the autogenerated file
+// using the provided suffix.
+func autogeneratedFileName(suffix string) string {
+	var baseName string
+	if *fileName == "" {
+		baseName = "mkcgo"
+	} else {
+		baseName = strings.TrimSuffix(*fileName, ".go")
+	}
+	return baseName + suffix
+}
+
 func writeTempSourceFile(data []byte) (string, error) {
 	f, err := os.CreateTemp("", "mkcgo-generated-*.go")
 	if err != nil {