2004-12-22 Paul Eggert <eggert@cs.ucla.edu>
+ * NEWS: Bison-generated parsers no longer default to using the
+ alloca function (when available) to extend the parser stack, due
+ to widespread problems in unchecked stack-overflow detection.
+ * data/glr.c (YYMAXDEPTH): Remove undef when zero. It's the user's
+ responsibility to set it to a positive value. This lets the user
+ specify a value that is not a preprocessor constant.
+ * data/yacc.c (YYMAXDEPTH): Likewise.
+ (YYSTACK_ALLOC): Define only if YYSTACK_USE_ALLOCA is nonzero.
+ * doc/bison.texinfo (Stack Overflow): YYMAXDEPTH no longer needs
+ to be a compile-time constant. However, explain the constraints on it.
+ Also, explain the constraints on YYINITDEPTH.
+ (Table of Symbols): Explain that alloca is no longer the default.
+ Explain the user's responsibility if they define YYSTACK_USE_ALLOCA
+ to 1.
+
* doc/bison.texinfo (Location Default Action): Mention that n must
be zero when k is zero. Suggested by Frank Heckenbach.
Changes in version 1.875f:
+* Bison-generated parsers no longer default to using the alloca function
+ (when available) to extend the parser stack, due to widespread
+ problems in unchecked stack-overflow detection. You can "#define
+ YYSTACK_USE_ALLOCA 1" to use alloca anyway, but please read the
+ manual to determine safe values for YYMAXDEPTH in that case.
+
Changes in version 1.875e, 2004-12-10:
* New directive: %initial-action.
# ifdef YYSTACK_USE_ALLOCA
# if YYSTACK_USE_ALLOCA
-# define YYSTACK_ALLOC alloca
-# endif
-# else
-# if defined (alloca) || defined (_ALLOCA_H)
-# define YYSTACK_ALLOC alloca
-# else
# ifdef __GNUC__
# define YYSTACK_ALLOC __builtin_alloca
+# else
+# define YYSTACK_ALLOC alloca
# endif
# endif
# endif
SIZE_MAX < YYSTACK_BYTES (YYMAXDEPTH)
evaluated with infinite-precision integer arithmetic. */
-#if defined (YYMAXDEPTH) && YYMAXDEPTH == 0
-# undef YYMAXDEPTH
-#endif
-
#ifndef YYMAXDEPTH
# define YYMAXDEPTH ]b4_stack_depth_max[
#endif
parser stack can become before a stack overflow occurs. Define the
macro with a value that is an integer. This value is the maximum number
of tokens that can be shifted (and not reduced) before overflow.
-It must be a constant expression whose value is known at compile time.
The stack space allowed is not necessarily allocated. If you specify a
large value for @code{YYMAXDEPTH}, the parser actually allocates a small
you do not need to make @code{YYMAXDEPTH} painfully small merely to save
space for ordinary inputs that do not need much stack.
+However, do not allow @code{YYMAXDEPTH} to be a value so large that
+arithmetic overflow could occur when calculating the size of the stack
+space. Also, do not allow @code{YYMAXDEPTH} to be less than
+@code{YYINITDEPTH}.
+
@cindex default stack limit
The default value of @code{YYMAXDEPTH}, if you do not define it, is
10000.
@vindex YYINITDEPTH
You can control how much stack is allocated initially by defining the
-macro @code{YYINITDEPTH}. This value too must be a compile-time
-constant integer. The default is 200.
+macro @code{YYINITDEPTH} to a positive integer. For the C
+@acronym{LALR}(1) parser, this value must be a compile-time constant
+unless you are assuming C99 or some other target language or compiler
+that allows variable-length arrays. The default is 200.
+
+Do not allow @code{YYINITDEPTH} to be a value so large that arithmetic
+overflow would occur when calculating the size of the stack space.
+Also, do not allow @code{YYINITDEPTH} to be greater than
+@code{YYMAXDEPTH}.
@c FIXME: C++ output.
Because of semantical differences between C and C++, the
@end deffn
@deffn {Macro} YYSTACK_USE_ALLOCA
-Macro used to control the use of @code{alloca}. If defined to @samp{0},
-the parser will not use @code{alloca} but @code{malloc} when trying to
-grow its internal stacks. Do @emph{not} define @code{YYSTACK_USE_ALLOCA}
-to anything else.
+Macro used to control the use of @code{alloca} when the C
+@acronym{LALR}(1) parser needs to extend its stacks. If defined to 0,
+the parser will use @code{malloc} to extend its stacks. If defined to
+1, the parser will use @code{alloca}. Values other than 0 and 1 are
+reserved for future Bison extensions. If not defined,
+@code{YYSTACK_USE_ALLOCA} defaults to 0.
+
+If you define @code{YYSTACK_USE_ALLOCA} to 1, it is your
+responsibility to make sure that @code{alloca} is visible, e.g., by
+using @acronym{GCC} or by including @code{<stdlib.h>}. Furthermore,
+in the all-too-common case where your code may run on a host with a
+limited stack and with unreliable stack-overflow checking, you should
+set @code{YYMAXDEPTH} to a value that cannot possibly result in
+unchecked stack overflow on any of your target hosts when
+@code{alloca} is called. You can inspect the code that Bison
+generates in order to determine the proper numeric values. This will
+require some expertise in low-level implementation details.
@end deffn
@deffn {Type} YYSTYPE
projects / bison.git / commitdiff
