On Wed, Dec 18, 2024 at 11:33:46AM +0100, Christoph Badura wrote:
> On Sun, Dec 15, 2024 at 08:34:35PM +0000, Patrick Welche wrote:
> > int main()
> > {
> > printf("%d", isspace(0xffffffffu));
> >
> > return 0;
> > }
> >
> > causes a segmentation fault on NetBSD-current/amd64, but returns 0 on
> > ubuntu 24. One could say "don't do that, 0xffffffffu isn't a valid char".
>
> Is that actual usage in the code or something whipped up to demonstrate
> the issue?
That is something whipped up to demonstrate what happens in the code.
A "minimal reproducer" if you will...
> > (That value was used in the program as "an EOF occured when that char
> > was read".)
>
> "an EOF occured when that char was read" leaves me stumped.
> Clearly, if you are able to read a char, you weren't at EOF and if you
> were at EOF you wouldn't be able to read a char. That's how Unix has
> worked forever.
The code is defining its own
#define ENDFILE 0xffffffffu /* Too large to be a character */
and using it instead of EOF (why bother?).
Using EOF instead would be fine, as it is an int and not an unsigned int, viz
isspace(0xffffffffu) and isspace(0xffffffff) give a segmentation fault
isspace((int)0xffffffff) and isspace(EOF) don't.
A small hurdle was "but it works on linux" hence the email to this list,
and John Kollasch pointed to the CAVEATS section of ctype(3) within
minutes - thanks!
Cheers,
Patrick
