Re: [bug-gnulib] Re: getdate don't need alloca

[Paul Eggert]

Simon Josefsson <address@hidden> writes:

> Not using alloca is still an option, I'm not sure what the other
> options are.

I thought of one more option: use a much smaller limit on the stack size.
This is feasible for getdate's grammar.

A couple of other things.  The Bison documentation says that
YYSTACK_USE_ALLOCA must be defined to 0 if it is defined to anything.
And there's an obsolete comment about AIX and alloca -- we no longer
use the alloca pragma, so this shouldn't be a problem.

I merged everybody's suggestions, tested the result with coreutils,
and installed the following patch, in both gnulib and coreutils.

2004-12-19  Paul Eggert  <address@hidden>

        * lib/alloca_.h: Conditionalize on _GNULIB_ALLOCA_H, not _ALLOCA_H.
        Remove now-obsolete comment about AIX.
        * lib/getdate.y: Include <alloca.h> only if HAVE_ALLOCA.
        (YYSTACK_USE_ALLOCA): Define to 0 if !HAVE_ALLOCA.
        (YYMAXDEPTH): New macro.
        * modules/getdate: Depend on alloca-opt, not alloca.

Index: lib/alloca_.h
===================================================================
RCS file: /cvsroot/gnulib/gnulib/lib/alloca_.h,v
retrieving revision 1.6
diff -p -u -r1.6 alloca_.h
--- lib/alloca_.h       11 Nov 2004 09:25:55 -0000      1.6
+++ lib/alloca_.h       19 Dec 2004 13:38:13 -0000
@@ -18,12 +18,10 @@
    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
    USA.  */
 
-/* When this file is included, it may be preceded only by preprocessor
-   declarations.  Thanks to AIX.  Therefore we include it right after
-   "config.h", not later.  */
-
-#ifndef _ALLOCA_H
-# define _ALLOCA_H
+/* Avoid using the symbol _ALLOCA_H here, as Bison assumes _ALLOCA_H
+   means there is a real alloca function.  */
+#ifndef _GNULIB_ALLOCA_H
+# define _GNULIB_ALLOCA_H
 
 /* alloca (N) returns a pointer to N bytes of memory
    allocated on the stack, which will last until the function returns.
@@ -51,4 +49,4 @@ extern "C"
 void *alloca (size_t);
 #endif
 
-#endif /* _ALLOCA_H */
+#endif /* _GNULIB_ALLOCA_H */
Index: lib/getdate.y
===================================================================
RCS file: /cvsroot/gnulib/gnulib/lib/getdate.y,v
retrieving revision 1.91
diff -p -u -r1.91 getdate.y
--- lib/getdate.y       8 Dec 2004 22:25:43 -0000       1.91
+++ lib/getdate.y       19 Dec 2004 13:38:13 -0000
@@ -36,7 +36,18 @@
 
 #include "getdate.h"
 
-#include <alloca.h>
+/* Use alloca only if it is known to be builtin.  */
+#if HAVE_ALLOCA
+# include <alloca.h>
+#else
+# define YYSTACK_USE_ALLOCA 0
+#endif
+
+/* Tell Bison ow much stack space is needed.  20 should be plenty for
+   this grammar, which is not right recursive.  Beware setting it too
+   high, since that might cause problems on machines whose alloca
+   implementations have lame stack-overflow checking.  */
+#define YYMAXDEPTH 20
 
 /* Since the code of getdate.y is not included in the Emacs executable
    itself, there is no need to #define static in this file.  Even if
Index: modules/getdate
===================================================================
RCS file: /cvsroot/gnulib/gnulib/modules/getdate,v
retrieving revision 1.9
diff -p -u -r1.9 getdate
--- modules/getdate     29 Oct 2004 21:00:24 -0000      1.9
+++ modules/getdate     19 Dec 2004 13:44:38 -0000
@@ -16,7 +16,7 @@ gettime
 mktime
 setenv
 xalloc
-alloca
+alloca-opt
 
 configure.ac:
 gl_GETDATE
@@ -34,4 +34,3 @@ GPL
 
 Maintainer:
 Paul Eggert
-