misc/cgo: generate Windows import libraries for clang

LLD won't import a .dll directly and instead requires an import library.
So generate these using -out-implib, the same way as was done in CL
312046, where it makes sense, and elsewhere build the import library
using a def file. We can't use -out-implib all the time, because the
output file gets overwritten each time the linker is called, rather than
merged.

Updates #46502.

Change-Id: Iefe54cb6c576004b83b1039ba673881b8640423d
Reviewed-on: https://go-review.googlesource.com/c/go/+/327211
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/misc/cgo/testcshared/cshared_test.go b/misc/cgo/testcshared/cshared_test.go
index fdc6df9602cceef41668c71e34fb4e7bf7822512..19ad8c76a838b54bad64c35635216088ff40db80 100644 (file)
--- a/misc/cgo/testcshared/cshared_test.go
+++ b/misc/cgo/testcshared/cshared_test.go
@@ -292,11 +292,60 @@ func createHeaders() error {
                "-installsuffix", "testcshared",
                "-o", libgoname,
                filepath.Join(".", "libgo", "libgo.go")}
+       if GOOS == "windows" && strings.HasSuffix(args[6], ".a") {
+               args[6] = strings.TrimSuffix(args[6], ".a") + ".dll"
+       }
        cmd = exec.Command(args[0], args[1:]...)
        out, err = cmd.CombinedOutput()
        if err != nil {
                return fmt.Errorf("command failed: %v\n%v\n%s\n", args, err, out)
        }
+       if GOOS == "windows" {
+               // We can't simply pass -Wl,--out-implib, because this relies on having imports from multiple packages,
+               // which results in the linkers output implib getting overwritten at each step. So instead build the
+               // import library the traditional way, using a def file.
+               err = os.WriteFile("libgo.def",
+                       []byte("LIBRARY libgo.dll\nEXPORTS\n\tDidInitRun\n\tDidMainRun\n\tDivu\n\tFromPkg\n\t_cgo_dummy_export\n"),
+                       0644)
+               if err != nil {
+                       return fmt.Errorf("unable to write def file: %v", err)
+               }
+               out, err = exec.Command(cc[0], append(cc[1:], "-print-prog-name=dlltool")...).CombinedOutput()
+               if err != nil {
+                       return fmt.Errorf("unable to find dlltool path: %v\n%s\n", err, out)
+               }
+               args := []string{strings.TrimSpace(string(out)), "-D", args[6], "-l", libgoname, "-d", "libgo.def"}
+
+               // This is an unfortunate workaround for https://github.com/mstorsjo/llvm-mingw/issues/205 in which
+               // we basically reimplement the contents of the dlltool.sh wrapper: https://git.io/JZFlU
+               dlltoolContents, err := os.ReadFile(args[0])
+               if err != nil {
+                       return fmt.Errorf("unable to read dlltool: %v\n", err)
+               }
+               if bytes.HasPrefix(dlltoolContents, []byte("#!/bin/sh")) && bytes.Contains(dlltoolContents, []byte("llvm-dlltool")) {
+                       base, name := filepath.Split(args[0])
+                       args[0] = filepath.Join(base, "llvm-dlltool")
+                       var machine string
+                       switch strings.SplitN(name, "-", 2)[0] {
+                       case "i686":
+                               machine = "i386"
+                       case "x86_64":
+                               machine = "i386:x86-64"
+                       case "armv7":
+                               machine = "arm"
+                       case "aarch64":
+                               machine = "arm64"
+                       }
+                       if len(machine) > 0 {
+                               args = append(args, "-m", machine)
+                       }
+               }
+
+               out, err = exec.Command(args[0], args[1:]...).CombinedOutput()
+               if err != nil {
+                       return fmt.Errorf("unable to run dlltool to create import library: %v\n%s\n", err, out)
+               }
+       }
 
        if runtime.GOOS != GOOS && GOOS == "android" {
                args = append(adbCmd(), "push", libgoname, fmt.Sprintf("%s/%s", androiddir, libgoname))
@@ -749,7 +798,12 @@ func TestGo2C2Go(t *testing.T) {
        defer os.RemoveAll(tmpdir)
 
        lib := filepath.Join(tmpdir, "libtestgo2c2go."+libSuffix)
-       run(t, nil, "go", "build", "-buildmode=c-shared", "-o", lib, "./go2c2go/go")
+       var env []string
+       if GOOS == "windows" && strings.HasSuffix(lib, ".a") {
+               env = append(env, "CGO_LDFLAGS=-Wl,--out-implib,"+lib, "CGO_LDFLAGS_ALLOW=.*")
+               lib = strings.TrimSuffix(lib, ".a") + ".dll"
+       }
+       run(t, env, "go", "build", "-buildmode=c-shared", "-o", lib, "./go2c2go/go")
 
        cgoCflags := os.Getenv("CGO_CFLAGS")
        if cgoCflags != "" {