Re: bison YYSTACK_ALLOC_MAXIMUM 4032 ?

[Paul Eggert]

address@hidden writes:

> Can the preset value of YYSTACK_ALLOC_MAXIMUM 4032
> be explained some more?

I added this comment:

2005-04-24  Paul Eggert  <address@hidden>

        * data/yacc.c (YYSTACK_ALLOC_MAXIMUM): Add more-descriptive comment.

Index: yacc.c
===================================================================
RCS file: /cvsroot/bison/bison/data/yacc.c,v
retrieving revision 1.85
retrieving revision 1.86
diff -p -u -r1.85 -r1.86
--- yacc.c      16 Apr 2005 06:25:03 -0000      1.85
+++ yacc.c      25 Apr 2005 03:14:22 -0000      1.86
@@ -239,6 +239,10 @@ b4_syncline(address@hidden@], address@hidden@])[
    /* Pacify GCC's `empty if-body' warning. */
 #  define YYSTACK_FREE(Ptr) do { /* empty */; } while (0)
 #  ifndef YYSTACK_ALLOC_MAXIMUM
+    /* The OS might guarantee only one guard page at the bottom of the stack,
+       and a page size can be as small as 4096 bytes.  So we cannot safely
+       invoke alloca (N) if N exceeds 4096.  Use a slightly smaller number
+       to allow for a few compiler-allocated temporary stack slots.  */
 #   define YYSTACK_ALLOC_MAXIMUM 4032 /* reasonable circa 2005 */
 #  endif
 # else