Re: Calling yyerror with non-literal parameter triggers warning

[Kaz Kylheku]

On 2019-08-19 13:05, August Karlstrom wrote:
> When I use the default C compiler cc on macOS to compile a parser
> generated by GNU Bison I get the following warning:
>
> y.tab.c:3974:18: warning: format string is not a string literal
>       (potentially insecure) [-Wformat-security]
>         yyerror (yymsgp);
>                  ^~~~~~
> y.tab.c:3974:18: note: treat the string as an argument to avoid this
>         yyerror (yymsgp);
>                  ^
>                  "%s",
>
> As the warning suggests, GNU Bison should instead generate the call
>
> yyerror ("%s", yymsgp);

That would almost certainly be wrong, since yyerror is a
one-argument function; its prototype is

  void yyerror(const char *);

(That is, that's the default one. Various Bison options can change
the type signature. The presence of %locations %define api.pure
adds a parameter to yyerror, as does %parse-param.)

A parser that needs to have a printf-like function should define
it as an auxiliary, e.g.:

   void yyerrorf(const char *fmt, ...)
   {
      /* vsnprintf into buffer */
      /* call yyerror(buffer) */
   }

Or possibly the other way around:

   void yyerror(const char *nofmt)
   {
      yyerrorf("%s", nofmt);
   }