cmd/pack: rename __.SYMDEF to __.GOSYMDEF

This fixes a problem with ELF tools thinking they know the
format of the symbol table, as we do not use any of the
standard formats for that table.

This change will probably annoy the Plan 9 users, but I
believe there are other incompatibilities already that mean
they have to use a Go-specific nm.

Fixes #3473.

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/6500117

src/cmd/5l/5.out.h

@@ -276,7 +276,7 @@ enum	as
 /*
  * this is the ranlib header
  */
-#define	SYMDEF	"__.SYMDEF"
+#define	SYMDEF	"__.GOSYMDEF"
 
 /*
  * this is the simulated IEEE floating point

src/cmd/6l/6.out.h

@@ -865,7 +865,7 @@ enum
 /*
  * this is the ranlib header
  */
-#define	SYMDEF	"__.SYMDEF"
+#define	SYMDEF	"__.GOSYMDEF"
 
 /*
  * this is the simulated IEEE floating point

src/cmd/8l/8.out.h

@@ -547,7 +547,7 @@ enum
 /*
  * this is the ranlib header
  */
-#define	SYMDEF	"__.SYMDEF"
+#define	SYMDEF	"__.GOSYMDEF"
 
 /*
  * this is the simulated IEEE floating point

src/cmd/gc/lex.c

@@ -480,7 +480,7 @@ skiptopkgdef(Biobuf *b)
 	if(memcmp(p, "!<arch>\n", 8) != 0)
 		return 0;
 	/* symbol table is first; skip it */
-	sz = arsize(b, "__.SYMDEF");
+	sz = arsize(b, "__.GOSYMDEF");
 	if(sz < 0)
 		return 0;
 	Bseek(b, sz, 1);

src/cmd/ld/lib.c

@@ -366,7 +366,7 @@ objfile(char *file, char *pkg)
 		return;
 	}
 	
-	/* skip over __.SYMDEF */
+	/* skip over __.GOSYMDEF */
 	off = Boffset(f);
 	if((l = nextar(f, off, &arhdr)) <= 0) {
 		diag("%s: short read on archive file symbol header", file);
@@ -402,7 +402,7 @@ objfile(char *file, char *pkg)
 	 * the individual symbols that are unused.
 	 *
 	 * loading every object will also make it possible to
-	 * load foreign objects not referenced by __.SYMDEF.
+	 * load foreign objects not referenced by __.GOSYMDEF.
 	 */
 	for(;;) {
 		l = nextar(f, off, &arhdr);

src/cmd/nm/nm.c

@@ -43,7 +43,7 @@ enum{
 
 char	*errs;			/* exit status */
 char	*filename;		/* current file */
-char	symname[]="__.SYMDEF";	/* table of contents file name */
+char	symname[]="__.GOSYMDEF";	/* table of contents file name */
 int	multifile;		/* processing multiple files */
 int	aflag;
 int	gflag;

src/cmd/pack/ar.c

@@ -111,7 +111,7 @@ char	*opt =		"uvnbailogS";
 char	artemp[] =	"/tmp/vXXXXX";
 char	movtemp[] =	"/tmp/v1XXXXX";
 char	tailtemp[] =	"/tmp/v2XXXXX";
-char	symdef[] =	"__.SYMDEF";
+char	symdef[] =	"__.GOSYMDEF";
 char	pkgdef[] =	"__.PKGDEF";
 
 int	aflag;				/* command line flags */

src/pkg/exp/types/exportdata.go

@@ -52,13 +52,14 @@ func FindGcExportData(r *bufio.Reader) (err error) {
 		var name string
 		var size int
 
-		// First entry should be __.SYMDEF.
+		// First entry should be __.GOSYMDEF.
+		// Older archives used __.SYMDEF, so allow that too.
 		// Read and discard.
 		if name, size, err = readGopackHeader(r); err != nil {
 			return
 		}
-		if name != "__.SYMDEF" {
-			err = errors.New("go archive does not begin with __.SYMDEF")
+		if name != "__.SYMDEF" && name != "__.GOSYMDEF" {
+			err = errors.New("go archive does not begin with __.SYMDEF or __.GOSYMDEF")
 			return
 		}
 		const block = 4096