compilepkg: cgo assembly uses the C compiler

go/tools/builders/compilepkg.go

@@ -273,6 +273,7 @@ func compileArchive(
 		hSrcs[i] = src.filename
 	}
 	haveCgo := len(cgoSrcs)+len(cSrcs)+len(cxxSrcs)+len(objcSrcs)+len(objcxxSrcs) > 0
+	packageUsesCgo := cgoEnabled && haveCgo
 
 	// Instrument source files for coverage.
 	if coverMode != "" {
@@ -329,12 +330,11 @@ func compileArchive(
 	// If we have cgo, generate separate C and go files, and compile the
 	// C files.
 	var objFiles []string
-	if cgoEnabled && haveCgo {
-		// TODO(#2006): Compile .s and .S files with cgo2, not the Go assembler.
-		// If cgo is not enabled or we don't have other cgo sources, don't
-		// compile .S files.
+	if packageUsesCgo {
+		// If the package uses Cgo, compile .s and .S files with cgo2, not the Go assembler.
+		// Otherwise: the .s/.S files will be compiled with the Go assembler later
 		var srcDir string
-		srcDir, goSrcs, objFiles, err = cgo2(goenv, goSrcs, cgoSrcs, cSrcs, cxxSrcs, objcSrcs, objcxxSrcs, nil, hSrcs, packagePath, packageName, cc, cppFlags, cFlags, cxxFlags, objcFlags, objcxxFlags, ldFlags, cgoExportHPath)
+		srcDir, goSrcs, objFiles, err = cgo2(goenv, goSrcs, cgoSrcs, cSrcs, cxxSrcs, objcSrcs, objcxxSrcs, sSrcs, hSrcs, packagePath, packageName, cc, cppFlags, cFlags, cxxFlags, objcFlags, objcxxFlags, ldFlags, cgoExportHPath)
 		if err != nil {
 			return err
 		}
@@ -355,7 +355,7 @@ func compileArchive(
 	if err != nil {
 		return err
 	}
-	if cgoEnabled && len(cgoSrcs) != 0 {
+	if packageUsesCgo {
 		// cgo generated code imports some extra packages.
 		imports["runtime/cgo"] = nil
 		imports["syscall"] = nil
@@ -458,28 +458,32 @@ func compileArchive(
 		}()
 	}
 
-	// If there are assembly files, and this is go1.12+, generate symbol ABIs.
+	// If there are Go assembly files and this is go1.12+: generate symbol ABIs.
+	// This excludes Cgo packages: they use the C compiler for assembly.
 	asmHdrPath := ""
 	if len(srcs.sSrcs) > 0 {
 		asmHdrPath = filepath.Join(workDir, "go_asm.h")
 	}
-	symabisPath, err := buildSymabisFile(goenv, srcs.sSrcs, srcs.hSrcs, asmHdrPath)
-	if symabisPath != "" {
-		if !goenv.shouldPreserveWorkDir {
-			defer os.Remove(symabisPath)
+	var symabisPath string
+	if !packageUsesCgo {
+		symabisPath, err = buildSymabisFile(goenv, srcs.sSrcs, srcs.hSrcs, asmHdrPath)
+		if symabisPath != "" {
+			if !goenv.shouldPreserveWorkDir {
+				defer os.Remove(symabisPath)
+			}
+		}
+		if err != nil {
+			return err
 		}
-	}
-	if err != nil {
-		return err
 	}
 
 	// Compile the filtered .go files.
 	if err := compileGo(goenv, goSrcs, packagePath, importcfgPath, embedcfgPath, asmHdrPath, symabisPath, gcFlags, pgoprofile, outPath); err != nil {
 		return err
 	}
 
-	// Compile the .s files.
-	if len(srcs.sSrcs) > 0 {
+	// Compile the .s files if we are not a cgo package; cgo is assembled by cc above
+	if len(srcs.sSrcs) > 0 && !packageUsesCgo {
 		includeSet := map[string]struct{}{
 			filepath.Join(os.Getenv("GOROOT"), "pkg", "include"): {},
 			workDir: {},

tests/core/cgo/asm/BUILD.bazel

@@ -0,0 +1,20 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "asm",
+    srcs = [
+        "asm_amd64.S",
+        "asm_arm64.S",
+        "cgoasm.go",
+    ],
+    cgo = True,
+    importpath = "github.com/bazelbuild/rules_go/tests/core/cgo/asm",
+)
+
+go_test(
+    name = "asm_test",
+    srcs = [
+        "cgoasm_test.go",
+    ],
+    embed = [":asm"],
+)

tests/core/cgo/asm/asm_amd64.S

@@ -0,0 +1,22 @@
+/*
+https://stackoverflow.com/questions/73435637/how-can-i-fix-usr-bin-ld-warning-trap-o-missing-note-gnu-stack-section-imp
+*/
+#if defined(__ELF__) && defined(__GNUC__)
+.section .note.GNU-stack,"",@progbits
+#endif
+
+/*
+define this symbol both with and without underscore.
+It seems like Mac OS X wants the underscore, but Linux does not.
+*/
+.global example_asm_func
+.global _example_asm_func
+.text
+example_asm_func:
+_example_asm_func:
+    mov $42, %rax
+    ret
+
+#if NOT_DEFINED
+#error "should not fail"
+#endif

tests/core/cgo/asm/asm_arm64.S

@@ -0,0 +1,15 @@
+/*
+define this symbol both with and without underscore.
+It seems like Mac OS X wants the underscore, but Linux does not.
+*/
+.global example_asm_func
+.global _example_asm_func
+.p2align 2 /* ld: warning: arm64 function not 4-byte aligned */
+example_asm_func:
+_example_asm_func:
+    mov x0, #44
+    ret
+
+#if NOT_DEFINED
+#error "should not fail"
+#endif

tests/core/cgo/asm/cgoasm.go

@@ -0,0 +1,12 @@
+//go:build amd64 || arm64
+
+package asm
+
+/*
+extern int example_asm_func();
+*/
+import "C"
+
+func callAssembly() int {
+	return int(C.example_asm_func())
+}

tests/core/cgo/asm/cgoasm_test.go

@@ -0,0 +1,23 @@
+//go:build amd64 || arm64
+
+package asm
+
+import (
+	"runtime"
+	"testing"
+)
+
+func TestNativeAssembly(t *testing.T) {
+	expectedGOARCH := map[string]int{
+		"amd64": 42,
+		"arm64": 44,
+	}
+	expected := expectedGOARCH[runtime.GOARCH]
+	if expected == 0 {
+		t.Fatalf("expected=0 for GOARCH=%s; missing value?", runtime.GOARCH)
+	}
+	actual := callAssembly()
+	if actual != expected {
+		t.Errorf("callAssembly()=%d; expected=%d", actual, expected)
+	}
+}