Update on the Modern C initiative - devel - Fedora mailing-lists

21 Dec 2023


      Based on my records, all issues that can lead to silent miscompilation
because of altered configure probes (autoconf/CMake and a few others)
have been addressed, or there are at least Bugzilla bugs filed for them.
There could be some gaps due to lack of architecture capture, general
rawhide churn, or configure scripts running late during the build, which
we do not reach due to a previous build failure.  But these gaps should
fairly small, I hope.  It's also not a new problem—while fixing newly
introduced errors, we encountered cases where autoconf probes had
already been failing unexpectedly for a long time because of typos or
missing #include directives.
I originally wanted to fix the int-conversion issues next.  That package
set is fairly small (about 60 packages).  But it's more or less a coin
toss whether the compiler errors is due to a missing cast due to C type
system limitations, or indicative of a real problem (typically
manifesting as a crash at run time if the code is ever executed).  The
latter can be quite difficult to fix and may require domain-specific
knowledge.  Just adding the cast in both cases just obscures the crash
or misbehavior in the second case, and robs us of an opportunity to fix
this properly.  I see what I can do to fix packages, but it's unlikely
that it will going to be all of them.
Looking at the calendar and the projected time when GCC 14 will land in
the buildroot, I think we missed the window where a GCC 13 version with
a preview of these C front end changes would have been beneficial to
Fedora developers.  It would have also created an awkward issue where
__GNUC__ is 13, but the compiler behaves in part like GCC 14.  This is
relevant if it's necessary to suppress (or treat as warnings)
-Wreturn-mismatch diagnostics, which only exist in GCC 14.
This brings me to my final point.  We still don't have a solution for
Vala. I plan to look at valac soon and see what we can do to keep things
at least compiling with GCC 14 (after re-running valac).
Thanks,
Florian