gopherjs · nevkontakte · Apr 7, 2024 · Apr 2, 2024
diff --git a/compiler/linkname.go b/compiler/linkname.go
@@ -75,6 +75,83 @@ func (n SymName) IsMethod() (recv string, method string, ok bool) {
 	return
 }
 
+// readLinknameFromComment reads the given comment to determine if it's a go:linkname
+// directive then returns the linkname information, otherwise returns nil.
+func readLinknameFromComment(pkgPath string, comment *ast.Comment) (*GoLinkname, error) {
+	if !strings.HasPrefix(comment.Text, `//go:linkname `) {
+		return nil, nil // Not a linkname compiler directive.
+	}
+
+	fields := strings.Fields(comment.Text)
+
+	// Check that the directive comment has both parts and is on the line by itself.
+	switch len(fields) {
+	case 2:
+		// Ignore one-argument form //go:linkname localName
+		// This is typically used with "insert"-style links to
+		// suppresses the usual error for a function that lacks a body.
+		// The "insert"-style links aren't supported by GopherJS so
+		// these bodiless functions have to be overridden in the natives anyway.
+		return nil, nil
+	case 3:
+		// Continue for two-argument form //go:linkname localName importPath.extName
+		break
+	default:
+		return nil, fmt.Errorf(`gopherjs: usage requires 2 arguments: //go:linkname localName importPath.extName`)
+	}
+
+	localPkg, localName := pkgPath, fields[1]
+	extPkg, extName := ``, fields[2]
+
+	if localName == extName {
+		// Ignore self referencing links, //go:linkname localName localName
+		// These function similar to one-argument links.
+		return nil, nil
+	}
+
+	pathOffset := 0
+	if pos := strings.LastIndexByte(extName, '/'); pos != -1 {
+		pathOffset = pos + 1
+	}
+
+	if idx := strings.IndexByte(extName[pathOffset:], '.'); idx != -1 {
+		extPkg, extName = extName[:pathOffset+idx], extName[pathOffset+idx+1:]
+	}
+
+	return &GoLinkname{
+		Reference:      SymName{PkgPath: localPkg, Name: localName},
+		Implementation: SymName{PkgPath: extPkg, Name: extName},
+	}, nil
+}
+
+// isMitigatedVarLinkname checks if the given go:linkname directive on
+// a variable, which GopherJS doesn't support, is known about.
+// We silently ignore such directives, since it doesn't seem to cause any problems.
+func isMitigatedVarLinkname(sym SymName) bool {
+	mitigatedLinks := map[string]bool{
+		`reflect.zeroVal`:         true,
+		`math/bits.overflowError`: true, // Defaults in bits_errors_bootstrap.go
+		`math/bits.divideError`:   true, // Defaults in bits_errors_bootstrap.go
+	}
+	return mitigatedLinks[sym.String()]
+}
+
+// isMitigatedInsertLinkname checks if the given go:linkname directive
+// on a function, where the function has a body, is known about.
+// These are unsupported "insert"-style go:linkname directives,
+// that we ignore as a link and handle case-by-case in native overrides.
+func isMitigatedInsertLinkname(sym SymName) bool {
+	mitigatedPkg := map[string]bool{
+		`runtime`:       true, // Lots of "insert"-style links
+		`internal/fuzz`: true, // Defaults to no-op stubs
+	}
+	mitigatedLinks := map[string]bool{
+		`internal/bytealg.runtime_cmpstring`: true,
+		`os.net_newUnixFile`:                 true,
+	}
+	return mitigatedPkg[sym.PkgPath] || mitigatedLinks[sym.String()]
+}
+
 // parseGoLinknames processed comments in a source file and extracts //go:linkname
 // compiler directive from the comments.
 //
@@ -98,63 +175,36 @@ func parseGoLinknames(fset *token.FileSet, pkgPath string, file *ast.File) ([]Go
 	isUnsafe := astutil.ImportsUnsafe(file)
 
 	processComment := func(comment *ast.Comment) error {
-		if !strings.HasPrefix(comment.Text, "//go:linkname ") {
-			return nil // Not a linkname compiler directive.
+		link, err := readLinknameFromComment(pkgPath, comment)
+		if err != nil || link == nil {
+			return err
 		}
 
-		// TODO(nevkontakte): Ideally we should check that the directive comment
-		// is on a line by itself, line Go compiler does, but ast.Comment doesn't
-		// provide an easy way to find that out.
-
 		if !isUnsafe {
 			return fmt.Errorf(`//go:linkname is only allowed in Go files that import "unsafe"`)
 		}
 
-		fields := strings.Fields(comment.Text)
-		if len(fields) != 3 {
-			return fmt.Errorf(`usage (all fields required): //go:linkname localname importpath.extname`)
-		}
-
-		localPkg, localName := pkgPath, fields[1]
-		extPkg, extName := "", fields[2]
-		if pos := strings.LastIndexByte(extName, '/'); pos != -1 {
-			if idx := strings.IndexByte(extName[pos+1:], '.'); idx != -1 {
-				extPkg, extName = extName[0:pos+idx+1], extName[pos+idx+2:]
-			}
-		} else if idx := strings.IndexByte(extName, '.'); idx != -1 {
-			extPkg, extName = extName[0:idx], extName[idx+1:]
-		}
-
-		obj := file.Scope.Lookup(localName)
+		obj := file.Scope.Lookup(link.Reference.Name)
 		if obj == nil {
-			return fmt.Errorf("//go:linkname local symbol %q is not found in the current source file", localName)
+			return fmt.Errorf("//go:linkname local symbol %q is not found in the current source file", link.Reference.Name)
 		}
 
 		if obj.Kind != ast.Fun {
-			if pkgPath == "math/bits" || pkgPath == "reflect" {
-				// These standard library packages are known to use go:linkname with
-				// variables, which GopherJS doesn't support. We silently ignore such
-				// directives, since it doesn't seem to cause any problems.
+			if isMitigatedVarLinkname(link.Reference) {
 				return nil
 			}
 			return fmt.Errorf("gopherjs: //go:linkname is only supported for functions, got %q", obj.Kind)
 		}
 
-		decl := obj.Decl.(*ast.FuncDecl)
-		if decl.Body != nil {
-			if pkgPath == "runtime" || pkgPath == "internal/bytealg" || pkgPath == "internal/fuzz" {
-				// These standard library packages are known to use unsupported
-				// "insert"-style go:linkname directives, which we ignore here and handle
-				// case-by-case in native overrides.
+		if decl := obj.Decl.(*ast.FuncDecl); decl.Body != nil {
+			if isMitigatedInsertLinkname(link.Reference) {
 				return nil
 			}
-			return fmt.Errorf("gopherjs: //go:linkname can not insert local implementation into an external package %q", extPkg)
+			return fmt.Errorf("gopherjs: //go:linkname can not insert local implementation into an external package %q", link.Implementation.PkgPath)
 		}
+
 		// Local function has no body, treat it as a reference to an external implementation.
-		directives = append(directives, GoLinkname{
-			Reference:      SymName{PkgPath: localPkg, Name: localName},
-			Implementation: SymName{PkgPath: extPkg, Name: extName},
-		})
+		directives = append(directives, *link)
 		return nil
 	}
 

diff --git a/compiler/linkname_test.go b/compiler/linkname_test.go
@@ -87,6 +87,7 @@ func TestSymName(t *testing.T) {
 func TestParseGoLinknames(t *testing.T) {
 	tests := []struct {
 		desc           string
+		pkgPath        string
 		src            string
 		wantError      string
 		wantDirectives []GoLinkname
@@ -148,14 +149,24 @@ func TestParseGoLinknames(t *testing.T) {
 			`,
 			wantError: `import "unsafe"`,
 		}, {
-			desc: "gopherjs: both parameters are required",
+			desc: "gopherjs: ignore one-argument linknames",
 			src: `package testcase
 
 			import _ "unsafe"
 
 			//go:linkname a
 			func a()
 			`,
+			wantDirectives: []GoLinkname{},
+		}, {
+			desc: `gopherjs: linkname has too many arguments`,
+			src: `package testcase
+
+			import _ "unsafe"
+
+			//go:linkname a other/package.a too/many.args
+			func a()
+			`,
 			wantError: "usage",
 		}, {
 			desc: "referenced function doesn't exist",
@@ -177,6 +188,17 @@ func TestParseGoLinknames(t *testing.T) {
 			var a string = "foo"
 			`,
 			wantError: `is only supported for functions`,
+		}, {
+			desc:    `gopherjs: ignore know referenced variables`,
+			pkgPath: `reflect`,
+			src: `package reflect
+
+			import _ "unsafe"
+
+			//go:linkname zeroVal other/package.zeroVal
+			var zeroVal []bytes
+			`,
+			wantDirectives: []GoLinkname{},
 		}, {
 			desc: "gopherjs: can not insert local implementation",
 			src: `package testcase
@@ -187,13 +209,60 @@ func TestParseGoLinknames(t *testing.T) {
 			func a() { println("do a") }
 			`,
 			wantError: `can not insert local implementation`,
+		}, {
+			desc:    `gopherjs: ignore known local implementation insert`,
+			pkgPath: `runtime`, // runtime is known and ignored
+			src: `package runtime
+
+			import _ "unsafe"
+
+			//go:linkname a other/package.a
+			func a() { println("do a") }
+			`,
+			wantDirectives: []GoLinkname{},
+		}, {
+			desc: `gopherjs: link to function with receiver`,
+			// //go:linkname <localname> <importpath>.<type>.<name>
+			src: `package testcase
+
+			import _ "unsafe"
+
+			//go:linkname a other/package.b.a
+			func a()
+			`,
+			wantDirectives: []GoLinkname{
+				{
+					Reference:      SymName{PkgPath: `testcase`, Name: `a`},
+					Implementation: SymName{PkgPath: `other/package`, Name: `b.a`},
+				},
+			},
+		}, {
+			desc: `gopherjs: link to function with pointer receiver`,
+			// //go:linkname <localname> <importpath>.<(*type)>.<name>
+			src: `package testcase
+
+			import _ "unsafe"
+
+			//go:linkname a other/package.*b.a
+			func a()
+			`,
+			wantDirectives: []GoLinkname{
+				{
+					Reference:      SymName{PkgPath: `testcase`, Name: `a`},
+					Implementation: SymName{PkgPath: `other/package`, Name: `*b.a`},
+				},
+			},
 		},
 	}
 
 	for _, test := range tests {
 		t.Run(test.desc, func(t *testing.T) {
 			file, fset := parseSource(t, test.src)
-			directives, err := parseGoLinknames(fset, "testcase", file)
+			pkgPath := `testcase`
+			if len(test.pkgPath) > 0 {
+				pkgPath = test.pkgPath
+			}
+			directives, err := parseGoLinknames(fset, pkgPath, file)
 
 			if test.wantError != "" {
 				if err == nil {

diff --git a/compiler/natives/src/net/fd_unix.go b/compiler/natives/src/net/fd_unix.go
@@ -0,0 +1,14 @@
+//go:build js
+// +build js
+
+package net
+
+import (
+	"os"
+	_ "unsafe" // for go:linkname
+)
+
+// Reversing the linkname direction
+//
+//go:linkname newUnixFile os.net_newUnixFile
+func newUnixFile(fd uintptr, name string) *os.File