[PATCH][util/macros] xorg-macros.m4.in: use the autoconf cache for XORG_CHECK_MALLOC_ZERO

[Burton, Ross]

Hi,

On 11 October 2013 02:23, Gaetan Nadon <memsize at videotron.ca> wrote:
> If all modules expanding the macro are setting $enableval to auto, then
> I think it works fine.

The macro doesn't take arguments, so by definition all modules are
using auto as the default unless the build system is explicitly
passing --enable-malloc0returnsnull or --disable-malloc0returnsnull.

> Now suppose a next module is configured using
> --disable-malloc0returnsnull, $enableval is now "no". The AC_LANG_PROGRAM
> is not executed, the value of xorg_cv_malloc0_returns_null is not
> changed (remains to the cached "yes" value), the value of
> MALLOC_ZERO_RETURNS_NULL does not change (remains to "yes") and value of
> *ZERO_CFLAGS do not change and are now wrong.

No.

If --disable is passed $enableval is "no" which is then assigned to
MALLOC_ZERO_RETURNS_NULL in the AC_ARG_ENABLE block (as before), which
results in the cache not being used and the test program not being ran
(as before).

> There are a number of permutations to check. Assuming the
> AC_LANG_PROGRAM test always return the same value, it may be preceeded
> by a module that was configured with enableval set to "yes" or "no".

That's not a problem as far as the test is concerned.  The cache isn't
written to by autoconf, only the user can do that.  If different
modules are compiled with different values for this test then they'll
"just" have different semantics for Xmalloc(0).

> I am also assuming that a module would not provide an alternate
> implementation of malloc which would break my assumption above.

Yes.  That's always been an assumption here and my test doesn't change
it.  Note that this only impacts users of Xmalloc() which is reducing
over time.

> I don't understand why someone would configure a module with --enable or
> --disable. Can you make sense out of this?

I'm not sure what you mean.  Personally I'd rip out the option
entirely and rely on autodetection (for native builds) with autoconf
site cache (for cross-compilation), but I left the patch in for
minimal impact on other users.

Ross