On Mon, Jan 16, 2023 at 08:42:32PM +0100, Miro Hrončok wrote:
> On 16. 01. 23 20:30, Siddhesh Poyarekar wrote:
> > If it is for distribution packages then I reckon the flags should be
> > as close as possible for the mere reason of consistency within the
> > distribution.
>
> Nope, the individual packages with extension modules all¹ use the
> %{build_cflags} flags by default.
>
> ¹: Technically they are required to and it is really hard not to do that noways.
>
> > If they're used for custom built modules (e.g. through
> > a tool that python auto-generates to build modules), then a very small
> > subset of the above flags would be necessary to retain binary
> > compatibility; you should be able to remove most of it.
>
> That is what I thought. Thank you.
Options like -m64/-m32 are ABI changing (but in %{optflags} these days
mostly uselessly because we don't usually cross-compile and gcc defaults to
those), -fsigned-char/-funsigned-char (I see it in redhat-rpm-config but
for armv3l/armv4b/armv4l which we don't build - in the past it was used on
more platforms) would be ABI changing, again on arm the various
-march=, -mfpu=, -mfloat-abi=, -mabi= options (but note that e.g. on most
other arches the -march= options aren't ABI changing, one just needs hw with
all the ISAs required by the built code), -fexceptions could be considered
partly ABI changing (at least say pthread_cancel through some objects
built with -fexceptions and others without that or with -fno-exceptions
will not destruct everything that should be after reaching frames without
it or similarly throwing C++ exceptions won't work well), so I'd suggest
to keep that one in. -mlong-double-{64,128} would be ABI changing, but
we just use compiler's default. -mabi={ibm,ieee}longdouble are ABI changing
on ppc64le too, but again we use the compiler defaults.
If you look at gcc documentation, many options are marked as ABI changing,
but I don't see them used in our %{optflags}...
So, when talking about options actually in use currently in f36/f37/f38 on
Fedora supported arches, I think -fexceptions is the only one I'd list.
Jakub
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