Re: UB in derivation.c

[Kaz Kylheku]

On 2022-11-01 14:26, Edoardo Sanguineti wrote:
> Hello,
> I think I found undefined behaviour in the function all_spaces in the file
> derivation.c
> I believe there is a missing cast to unsigned char before the call to the
> function c_isspace (see here:
> https://git.savannah.gnu.org/cgit/bison.git/tree/src/derivation.c#n166).

Your remarks would be correct about the ill-designed isspace function in
ISO C. This is c_isspace from gnulib, which looks like this:

  C_CTYPE_INLINE bool
  c_isspace (int c)
  {
    switch (c)
      {
      case ' ': case '\t': case '\n': case '\v': case '\f': case '\r':
        return true;
      default:
        return false;
      }
  }

It is not using the argument as an index into a table, and so there is no
risk of out-of-bounds access due to the argument being negative.

Also, the behavior won't change if something in the process accidentally
calls setlocale, which is laudable.

ISO C provides very few text processing functions that don't fall
victim to localization effects.

Think you can lexically scan a floating-point number in C syntax with
strtod? Check again: if the program has switched to a locale in which
the comma serves as the decimal point, "1.234E+15" won't be understood
properly by strotd.

> I searched all usages of c_isspace in the source code of bison and this is
> the only occurrence the cast to unsigned char is missing so I think that
> should be fixed.

Rather, the other unsigned char casts may be a hyper-correction
probably left over from previous versions of the code before gnulib.