cmd/gc, cmd/ld: use go.weak instead of weak as the weak symbol prefix

Also defend our symbol prefixes (now just "go" and "type")
from use as import paths.

Fixes #4257.

R=ken2
CC=golang-dev
https://golang.org/cl/6744072

src/cmd/gc/export.c

@@ -393,6 +393,8 @@ importimport(Sym *s, Strlit *z)
 	// human-readable messages.
 	Pkg *p;
 
+	if(isbadimport(z))
+		errorexit();
 	p = mkpkg(z);
 	if(p->name == nil) {
 		p->name = s->name;

src/cmd/gc/go.y

@@ -1030,10 +1030,16 @@ sym:
 hidden_importsym:
 	'@' LLITERAL '.' LNAME
 	{
+		Pkg *p;
+
 		if($2.u.sval->len == 0)
-			$$ = pkglookup($4->name, importpkg);
-		else
-			$$ = pkglookup($4->name, mkpkg($2.u.sval));
+			p = importpkg;
+		else {
+			if(isbadimport($2.u.sval))
+				errorexit();
+			p = mkpkg($2.u.sval);
+		}
+		$$ = pkglookup($4->name, p);
 	}
 
 name:

src/cmd/gc/lex.c

@@ -216,9 +216,9 @@ main(int argc, char *argv[])
 	typepkg = mkpkg(strlit("type"));
 	typepkg->name = "type";
 
-	weaktypepkg = mkpkg(strlit("weak.type"));
-	weaktypepkg->name = "weak.type";
-	weaktypepkg->prefix = "weak.type";  // not weak%2etype
+	weaktypepkg = mkpkg(strlit("go.weak.type"));
+	weaktypepkg->name = "go.weak.type";
+	weaktypepkg->prefix = "go.weak.type";  // not go%2eweak%2etype
 
 	unsafepkg = mkpkg(strlit("unsafe"));
 	unsafepkg->name = "unsafe";
@@ -664,6 +664,11 @@ importfile(Val *f, int line)
 		strcat(cleanbuf, path->s);
 		cleanname(cleanbuf);
 		path = strlit(cleanbuf);
+		
+		if(isbadimport(path)) {
+			fakeimport();
+			return;
+		}
 	}
 
 	if(!findpkg(path)) {

src/cmd/gc/subr.c

@@ -3572,9 +3572,6 @@ mkpkg(Strlit *path)
 	Pkg *p;
 	int h;
 
-	if(isbadimport(path))
-		errorexit();
-	
 	h = stringhash(path->s) & (nelem(phash)-1);
 	for(p=phash[h]; p; p=p->link)
 		if(p->path->len == path->len && memcmp(path->s, p->path->s, path->len) == 0)
@@ -3623,9 +3620,15 @@ addinit(Node **np, NodeList *init)
 	n->ullman = UINF;
 }
 
+static char* reservedimports[] = {
+	"go",
+	"type",
+};
+
 int
 isbadimport(Strlit *path)
 {
+	int i;
 	char *s;
 	Rune r;
 
@@ -3633,6 +3636,13 @@ isbadimport(Strlit *path)
 		yyerror("import path contains NUL");
 		return 1;
 	}
+	
+	for(i=0; i<nelem(reservedimports); i++) {
+		if(strcmp(path->s, reservedimports[i]) == 0) {
+			yyerror("import path \"%s\" is reserved and cannot be used", path->s);
+			return 1;
+		}
+	}
 
 	s = path->s;
 	while(*s) {

src/cmd/gc/y.tab.h

-/* A Bison parser, made by GNU Bison 2.6.2.  */
+/* A Bison parser, made by GNU Bison 2.3.  */
 
-/* Bison interface for Yacc-like parsers in C
-   
-      Copyright (C) 1984, 1989-1990, 2000-2012 Free Software Foundation, Inc.
-   
-   This program is free software: you can redistribute it and/or modify
+/* Skeleton interface for Bison's Yacc-like parsers in C
+
+   Copyright (C) 1984, 1989, 1990, 2000, 2001, 2002, 2003, 2004, 2005, 2006
+   Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
-   the Free Software Foundation, either version 3 of the License, or
-   (at your option) any later version.
-   
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
-   
+
    You should have received a copy of the GNU General Public License
-   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor,
+   Boston, MA 02110-1301, USA.  */
 
 /* As a special exception, you may create a larger work that contains
    part or all of the Bison parser skeleton and distribute that work
@@ -26,20 +29,10 @@
    special exception, which will cause the skeleton and the resulting
    Bison output files to be licensed under the GNU General Public
    License without this special exception.
-   
+
    This special exception was added by the Free Software Foundation in
    version 2.2 of Bison.  */
 
-#ifndef YY_Y_TAB_H
-# define YY_Y_TAB_H
-/* Enabling traces.  */
-#ifndef YYDEBUG
-# define YYDEBUG 0
-#endif
-#if YYDEBUG
-extern int yydebug;
-#endif
-
 /* Tokens.  */
 #ifndef YYTOKENTYPE
 # define YYTOKENTYPE
@@ -150,42 +143,25 @@ extern int yydebug;
 
 
 
+
 #if ! defined YYSTYPE && ! defined YYSTYPE_IS_DECLARED
 typedef union YYSTYPE
-{
-/* Line 2049 of yacc.c  */
 #line 28 "go.y"
-
+{
 	Node*		node;
 	NodeList*		list;
 	Type*		type;
 	Sym*		sym;
 	struct	Val	val;
 	int		i;
-
-
-/* Line 2049 of yacc.c  */
-#line 169 "y.tab.h"
-} YYSTYPE;
-# define YYSTYPE_IS_TRIVIAL 1
+}
+/* Line 1529 of yacc.c.  */
+#line 160 "y.tab.h"
+	YYSTYPE;
 # define yystype YYSTYPE /* obsolescent; will be withdrawn */
 # define YYSTYPE_IS_DECLARED 1
+# define YYSTYPE_IS_TRIVIAL 1
 #endif
 
 extern YYSTYPE yylval;
 
-#ifdef YYPARSE_PARAM
-#if defined __STDC__ || defined __cplusplus
-int yyparse (void *YYPARSE_PARAM);
-#else
-int yyparse ();
-#endif
-#else /* ! YYPARSE_PARAM */
-#if defined __STDC__ || defined __cplusplus
-int yyparse (void);
-#else
-int yyparse ();
-#endif
-#endif /* ! YYPARSE_PARAM */
-
-#endif /* !YY_Y_TAB_H  */

src/cmd/ld/go.c

@@ -643,7 +643,7 @@ mark(Sym *s)
 
 	if(s == S || s->reachable)
 		return;
-	if(strncmp(s->name, "weak.", 5) == 0)
+	if(strncmp(s->name, "go.weak.", 8) == 0)
 		return;
 	s->reachable = 1;
 	if(s->text)
@@ -751,7 +751,7 @@ deadcode(void)
 		last->next = nil;
 	
 	for(s = allsym; s != S; s = s->allsym)
-		if(strncmp(s->name, "weak.", 5) == 0) {
+		if(strncmp(s->name, "go.weak.", 8) == 0) {
 			s->special = 1;  // do not lay out in data segment
 			s->reachable = 1;
 			s->hide = 1;
@@ -766,8 +766,8 @@ doweak(void)
 	// resolve weak references only if
 	// target symbol will be in binary anyway.
 	for(s = allsym; s != S; s = s->allsym) {
-		if(strncmp(s->name, "weak.", 5) == 0) {
-			t = rlookup(s->name+5, s->version);
+		if(strncmp(s->name, "go.weak.", 8) == 0) {
+			t = rlookup(s->name+8, s->version);
 			if(t && t->type != 0 && t->reachable) {
 				s->value = t->value;
 				s->type = t->type;