Re: PATH_MAX and test-stat.h

[James Youngman]

On Sat, Jun 18, 2011 at 8:33 PM, Bruno Haible <address@hidden> wrote:
> Hi Eric,
>
> In pathmax.h one of the possible replacement values for PATH_MAX on systems
> that don't define it (currently HP-UX and GNU/Hurd) is an expression
> involving pathconf().
>
> But tests/test-stat.h line 20 declares an array of size PATH_MAX. So - at
> least with pre-C99 compilers - it is assuming that PATH_MAX is a constant.
>
> Should we guarantee that PATH_MAX is a constant expression (by modifying
> lib/pathmax.h), or change tests/test-stat.h to not assume it?

It looks to me like POSIX doesn't state that PATH_MAX is a constant
expression.   There are other values in limits.h that POSIX states
must be constant expressions (for example, INT_MAX) so I think this is
deliberate.

I suspect that the most useful thing we can do in gnulib is define
PATH_MAX to a non-constant expression on all platforms, even the ones
in which it is normally a constant expression.   Otherwise maintainers
will find that their code works on their system but won't compile on
some other system they don't have access to.    Clearly this position
on PATH_MAX could be taken to its logical conclusion of un-defining
the macro on all platforms to make sure that all GNU programs work on
Hurd, but I think that discussion has already been had.   In any case,
maintainers who want to go in for this can probably achieve the same
sort of effect with a syntax check.

As for tests/test-stat.h, I'm mildly surprised that we haven't seen
any systems where an auto buffer of size PATH_MAX blows the stack.
The only purpose for which test-stat.h uses this array is to verify
that stat-ing "." and cwd gives the same device/inode.   So for this
example we can probably just rely on getcwd-lgpl and call getcwd(NULL,
0).

James.