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* NEWS: Bison-generated parsers no longer default to using the

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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.
This commit is contained in:
Paul Eggert
2004-12-22 21:19:47 +00:00
parent 0a2c51373a
commit d7e14fc000
5 changed files with 54 additions and 21 deletions
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38
doc/bison.texinfo
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@@ -5574,7 +5574,6 @@ By defining the macro @code{YYMAXDEPTH}, you can control how deep the
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
@@ -5583,14 +5582,26 @@ increasing allocation happens automatically and silently. Therefore,
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
@@ -7306,10 +7317,23 @@ syntax error. @xref{Action Features, ,Special Features for Use in Actions}.
@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