Re: fixed size stack

[Akim Demaille]

Le 17 juil. 2012 à 10:00, Claudio Eterno a écrit :

> Hi folks,
> I'm writing here due to some configuration problems on bison.
> My question: I would like to use bison for an embedded application (based
> on a uC with only 16kb of ram a 256 kb of flash). Due to the limited
> resources reasons and also I know exactly the maximum size of
> the necessary stack, I don't want to occupy the memory with me unuseful
> library functions (like malloc for example). Anyway, is this possible to
> remove the alloc/malloc/realloc functions during compilation?

Hi Claudio,

A quick test seems to be conclusive.  Did you experiment
differently?

$ cat /tmp/foo.y
%code
{
# include <stdio.h>
# define YYINITDEPTH 10
# define YYMAXDEPTH YYINITDEPTH

  void
  yyerror(const char* msg)
  {
    fprintf (stderr, "%s\n", msg);
  }

  void *malloc(size_t s)
  {
    (void) s;
    yyerror ("called malloc");
    return 0;
  }

  int
  yylex()
  {
    return '1';
  }
}

%%
exp: '1' | '1' exp;
%%

int
main ()
{
  return !!yyparse();
}
$ bison foo.y
$ gcc-mp-4.8 -Wall -Wextra foo.tab.c
$ ./a.out
memory exhausted
$ nm a.out
0000000100002060 S _NXArgc
0000000100002068 S _NXArgv
0000000100002078 S ___progname
                 U ___stderrp
0000000100000000 A __mh_execute_header
0000000100002070 S _environ
                 U _exit
                 U _fprintf
                 U _free
0000000100001c70 T _main
0000000100001540 T _malloc
                 U _memcpy
0000000100002000 s _pvars
0000000100002080 S _yychar
0000000100001e7c s _yycheck
0000000100001e6a s _yydefact
0000000100001e6f s _yydefgoto
000000010000156a t _yydestruct
0000000100001510 T _yyerror
000000010000155f T _yylex
0000000100002084 S _yylval
0000000100002088 S _yynerrs
0000000100001e71 s _yypact
000000010000158f T _yyparse
0000000100001e76 s _yypgoto
0000000100001e62 s _yyr1
0000000100001e66 s _yyr2
0000000100001e80 s _yystos
0000000100001e78 s _yytable
0000000100001d60 s _yytranslate
                 U dyld_stub_binder
00000001000014d4 T start
$

You show read the generated code, and see, for instance,
that verbose error message for instance, do require malloc.