cmd/cgo: only write _cgo_flags for gccgo

We only use it for gccgo. Also only write out LDFLAGS,
as that is all that cmd/go uses.

Fixes #60642

Change-Id: I6ccc419a17a433583d9868dd63aa7ec41c2b22c4
Reviewed-on: https://go-review.googlesource.com/c/go/+/524556
Auto-Submit: Ian Lance Taylor <iant@google.com>
Commit-Queue: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>

4 files changed, 14 insertions, 15 deletions

diff --git a/src/cmd/cgo/doc.go b/src/cmd/cgo/doc.go
index 894df2d836..1f635d7c09 100644
--- a/src/cmd/cgo/doc.go
+++ b/src/cmd/cgo/doc.go
@@ -710,7 +710,7 @@ files:
 	_cgo_export.c   # for gcc
 	_cgo_export.h   # for gcc
 	_cgo_main.c     # for gcc
-	_cgo_flags      # for alternative build tools
+	_cgo_flags      # for build tool (if -gccgo)
 
 The file x.cgo1.go is a copy of x.go with the import "C" removed and
 references to C.xxx replaced with names like _Cfunc_xxx or _Ctype_xxx.
diff --git a/src/cmd/cgo/gcc.go b/src/cmd/cgo/gcc.go
index 28dc2a9bf8..d30056ec84 100644
--- a/src/cmd/cgo/gcc.go
+++ b/src/cmd/cgo/gcc.go
@@ -104,10 +104,8 @@ func (f *File) ProcessCgoDirectives() {
 	f.Preamble = strings.Join(linesOut, "\n")
 }
 
-// addToFlag appends args to flag. All flags are later written out onto the
-// _cgo_flags file for the build system to use.
+// addToFlag appends args to flag.
 func (p *Package) addToFlag(flag string, args []string) {
-	p.CgoFlags[flag] = append(p.CgoFlags[flag], args...)
 	if flag == "CFLAGS" {
 		// We'll also need these when preprocessing for dwarf information.
 		// However, discard any -g options: we need to be able
@@ -118,6 +116,9 @@ func (p *Package) addToFlag(flag string, args []string) {
 			}
 		}
 	}
+	if flag == "LDFLAGS" {
+		p.LdFlags = append(p.LdFlags, args...)
+	}
 }
 
 // splitQuoted splits the string s around each instance of one or more consecutive
diff --git a/src/cmd/cgo/main.go b/src/cmd/cgo/main.go
index 55f9cdc318..fce2671c2c 100644
--- a/src/cmd/cgo/main.go
+++ b/src/cmd/cgo/main.go
@@ -38,7 +38,7 @@ type Package struct {
 	IntSize     int64
 	GccOptions  []string
 	GccIsClang  bool
-	CgoFlags    map[string][]string // #cgo flags (CFLAGS, LDFLAGS)
+	LdFlags     []string // #cgo LDFLAGS
 	Written     map[string]bool
 	Name        map[string]*Name // accumulated Name from Files
 	ExpFunc     []*ExpFunc       // accumulated ExpFunc from Files
@@ -475,7 +475,6 @@ func newPackage(args []string) *Package {
 	p := &Package{
 		PtrSize:     ptrSize,
 		IntSize:     intSize,
-		CgoFlags:    make(map[string][]string),
 		Written:     make(map[string]bool),
 		noCallbacks: make(map[string]bool),
 		noEscapes:   make(map[string]bool),
diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go
index 947c61b5c5..8e1b5d62fd 100644
--- a/src/cmd/cgo/out.go
+++ b/src/cmd/cgo/out.go
@@ -45,18 +45,17 @@ func (p *Package) writeDefs() {
 
 	var gccgoInit strings.Builder
 
-	fflg := creat(*objDir + "_cgo_flags")
-	for k, v := range p.CgoFlags {
-		for _, arg := range v {
-			fmt.Fprintf(fflg, "_CGO_%s=%s\n", k, arg)
+	if !*gccgo {
+		for _, arg := range p.LdFlags {
+			fmt.Fprintf(fgo2, "//go:cgo_ldflag %q\n", arg)
 		}
-		if k == "LDFLAGS" && !*gccgo {
-			for _, arg := range v {
-				fmt.Fprintf(fgo2, "//go:cgo_ldflag %q\n", arg)
-			}
+	} else {
+		fflg := creat(*objDir + "_cgo_flags")
+		for _, arg := range p.LdFlags {
+			fmt.Fprintf(fflg, "_CGO_LDFLAGS=%s\n", arg)
 		}
+		fflg.Close()
 	}
-	fflg.Close()
 
 	// Write C main file for using gcc to resolve imports.
 	fmt.Fprintf(fm, "#include <stddef.h>\n") // For size_t below.