cmd/gc: implement -pack flag

The -pack flag causes 5g, 6g, 8g to write a Go archive directly,
instead of requiring the use of 'go tool pack' to convert the .5/.6/.8
to .a format.

Writing directly avoids the copy and also avoids having the
export data stored twice in the archive (once in __.PKGDEF,
once in .5/.6/.8).

A separate CL will enable the use of this flag by cmd/go.

Other build systems that do not know about -pack will be unaffected.

The changes to cmd/ld handle a minor simplification to the format:
an unused section is removed.

R=iant, r
CC=golang-dev
https://golang.org/cl/42880043

src/cmd/gc/export.c

@@ -354,7 +354,7 @@ dumpexport(void)
 
 	lno = lineno;
 
-	Bprint(bout, "\n$$  // exports\n    package %s", localpkg->name);
+	Bprint(bout, "\n$$\npackage %s", localpkg->name);
 	if(safemode)
 		Bprint(bout, " safe");
 	Bprint(bout, "\n");
@@ -369,8 +369,7 @@ dumpexport(void)
 		dumpsym(l->n->sym);
 	}
 
-	Bprint(bout, "\n$$  // local types\n\n$$\n");   // 6l expects this. (see ld/go.c)
-
+	Bprint(bout, "\n$$\n");
 	lineno = lno;
 }
 

src/cmd/gc/go.h

@@ -977,6 +977,7 @@ EXTERN	Link*	ctxt;
 EXTERN	int	nointerface;
 EXTERN	int	fieldtrack_enabled;
 EXTERN	int	precisestack_enabled;
+EXTERN	int	writearchive;
 
 EXTERN	Biobuf	bstdout;
 

src/cmd/gc/lex.c

@@ -267,6 +267,7 @@ main(int argc, char *argv[])
 	flagcount("m", "print optimization decisions", &debug['m']);
 	flagstr("o", "obj: set output file", &outfile);
 	flagstr("p", "path: set expected package import path", &myimportpath);
+	flagcount("pack", "write package file instead of object file", &writearchive);
 	flagcount("r", "debug generated wrappers", &debug['r']);
 	flagcount("race", "enable race detector", &flag_race);
 	flagcount("s", "warn about composite literals that can be simplified", &debug['s']);
@@ -518,12 +519,13 @@ skiptopkgdef(Biobuf *b)
 		return 0;
 	if(memcmp(p, "!<arch>\n", 8) != 0)
 		return 0;
-	/* symbol table is first; skip it */
+	/* symbol table may be first; skip it */
 	sz = arsize(b, "__.GOSYMDEF");
-	if(sz < 0)
-		return 0;
-	Bseek(b, sz, 1);
-	/* package export block is second */
+	if(sz >= 0)
+		Bseek(b, sz, 1);
+	else
+		Bseek(b, 8, 0);
+	/* package export block is next */
 	sz = arsize(b, "__.PKGDEF");
 	if(sz <= 0)
 		return 0;

src/cmd/gc/obj.c

@@ -12,10 +12,25 @@
 
 static	void	dumpglobls(void);
 
+enum
+{
+	ArhdrSize = 60
+};
+
+static void
+formathdr(char *arhdr, char *name, vlong size)
+{
+	snprint(arhdr, ArhdrSize, "%-16s%-12d%-6d%-6d%-8o%-10d`",
+		name, 0, 0, 0, 0644, size);
+	arhdr[ArhdrSize-1] = '\n'; // overwrite \0 written by snprint
+}
+
 void
 dumpobj(void)
 {
 	NodeList *externs, *tmp;
+	char arhdr[ArhdrSize];
+	vlong startobj, size;
 	Sym *zero;
 
 	bout = Bopen(outfile, OWRITE);
@@ -25,10 +40,33 @@ dumpobj(void)
 		errorexit();
 	}
 
+	startobj = 0;
+	if(writearchive) {
+		Bwrite(bout, "!<arch>\n", 8);
+		memset(arhdr, 0, sizeof arhdr);
+		Bwrite(bout, arhdr, sizeof arhdr);
+		startobj = Boffset(bout);
+	}
 	Bprint(bout, "go object %s %s %s %s\n", getgoos(), thestring, getgoversion(), expstring());
-	Bprint(bout, "  exports automatically generated from\n");
-	Bprint(bout, "  %s in package \"%s\"\n", curio.infile, localpkg->name);
 	dumpexport();
+	
+	if(writearchive) {
+		Bflush(bout);
+		size = Boffset(bout) - startobj;
+		if(size&1)
+			Bputc(bout, 0);
+		Bseek(bout, startobj - ArhdrSize, 0);
+		formathdr(arhdr, "__.PKGDEF", size);
+		Bwrite(bout, arhdr, ArhdrSize);
+		Bflush(bout);
+
+		Bseek(bout, startobj + size + (size&1), 0);
+		memset(arhdr, 0, ArhdrSize);
+		Bwrite(bout, arhdr, ArhdrSize);
+		startobj = Boffset(bout);
+		Bprint(bout, "go object %s %s %s %s\n", getgoos(), thestring, getgoversion(), expstring());
+	}
+
 	Bprint(bout, "\n!\n");
 
 	externs = nil;
@@ -51,6 +89,16 @@ dumpobj(void)
 	dumpdata();
 	linkwriteobj(ctxt, bout);
 
+	if(writearchive) {
+		Bflush(bout);
+		size = Boffset(bout) - startobj;
+		if(size&1)
+			Bputc(bout, 0);
+		Bseek(bout, startobj - ArhdrSize, 0);
+		snprint(namebuf, sizeof namebuf, "_go_.%c", thechar);
+		formathdr(arhdr, namebuf, size);
+		Bwrite(bout, arhdr, ArhdrSize);
+	}
 	Bterm(bout);
 }
 

src/cmd/ld/go.c

@@ -151,28 +151,11 @@ ldpkg(Biobuf *f, char *pkg, int64 len, char *filename, int whence)
 		}
 		loadpkgdata(filename, pkg, p0, p1 - p0);
 	}
-
-	// The __.PKGDEF archive summary has no local types.
+	
+	// __.PKGDEF has no cgo section - those are in the C compiler-generated object files.
 	if(whence == Pkgdef)
 		return;
 
-	// local types begin where exports end.
-	// skip rest of line after $$ we found above
-	p0 = p1 + 3;
-	while(*p0 != '\n' && *p0 != '\0')
-		p0++;
-
-	// local types end at next \n$$.
-	p1 = strstr(p0, "\n$$");
-	if(p1 == nil) {
-		fprint(2, "%s: cannot find end of local types in %s\n", argv0, filename);
-		if(debug['u'])
-			errorexit();
-		return;
-	}
-
-	loadpkgdata(filename, pkg, p0, p1 - p0);
-
 	// look for cgo section
 	p0 = strstr(p1, "\n$$  // cgo");
 	if(p0 != nil) {

src/cmd/ld/lib.c

@@ -327,25 +327,22 @@ objfile(char *file, char *pkg)
 		return;
 	}
 	
-	/* skip over __.GOSYMDEF */
+	/* skip over optional __.GOSYMDEF and process __.PKGDEF */
 	off = Boffset(f);
 	if((l = nextar(f, off, &arhdr)) <= 0) {
 		diag("%s: short read on archive file symbol header", file);
 		goto out;
 	}
-	if(strncmp(arhdr.name, symname, strlen(symname))) {
-		diag("%s: first entry not symbol header", file);
-		goto out;
-	}
-	off += l;
-	
-	/* skip over (or process) __.PKGDEF */
-	if((l = nextar(f, off, &arhdr)) <= 0) {
-		diag("%s: short read on archive file symbol header", file);
-		goto out;
+	if(strncmp(arhdr.name, symname, strlen(symname)) == 0) {
+		off += l;
+		if((l = nextar(f, off, &arhdr)) <= 0) {
+			diag("%s: short read on archive file symbol header", file);
+			goto out;
+		}
 	}
+
 	if(strncmp(arhdr.name, pkgname, strlen(pkgname))) {
-		diag("%s: second entry not package header", file);
+		diag("%s: cannot find package header", file);
 		goto out;
 	}
 	off += l;