Re: [PATCH 1/1] fs/qnx6: Fix building with GCC 15

From: Al Viro
Date: Sun Oct 06 2024 - 16:00:58 EST


On Sun, Oct 06, 2024 at 07:38:07PM +0000, David Laight wrote:
> ...
> > would explain what was really going on - the point is not to make gcc STFU, it's
> > to make the code more straightforward. The warning is basically "it smells
> > somewhat fishy around >here<, might be worth taking a look". And yes, it turned
> > out to be fishy; minimal "make it STFU" would be to strip those NULs from
> > the initializers (i.e. just go for static char match_root[2][3] = {".", ".."}; -
> > an array initializer is zero-padded if it's shorter than the array), but that
> > wasn't the only, er, oddity in that code.
>
> Indeed - looks like it is checking that the first two directory entries
> are "." and ".." in about the most complex way possible.
>
> I have vague recollections on some code that ignored the first two entries
> because they 'must be "." and ".."' - and then failed because some filesystem
> (and I can't even remember the O/S) didn't meet its expectations!
>
> A simple:
> if (strcmp(dir_entry[0].de_fname, ".") || strcmp(dir_entry[1].de_fname, ".."))
> error = 1;
> would suffice.

memcmp(), please. strcmp() is _not_ guaranteed to be safe without both being
NUL-terminated; yes, compiler will almost simplify that in case when one of
the arguments is a string literal, but it's better to do straight memcmp() in
this case. It's not worth trying to be fancy there...