Re: [PATCH] ltmain.in: don't suppress output for PIC compilations

[Ileana Dumitrescu]

Hi Sam,

On 15/08/2024 18:55, Sam James wrote:
> Sam James <sam@gentoo.org> writes:
>
> > I just hit this in a fascinating place.
> >
> > When working on xz, I set `-Werror=suggest-attribute=returns_nonnull`, and
> > the build failed (as I expected it to), but with no visible error from
> > the compiler.
> >
> > There's a mysterious '>/dev/null 2>&1' on the second line where
> > liblzma_la-common.o is built without PIC.
> >
> > With -fPIC, IPA doesn't end up doing attribute discovery. Without it,
> > it does. This behaviour is insane and we should patch it out.
> >
> > Bug: https://bugs.gentoo.org/135865
> > Cc: glaubitz@physik.fu-berlin.de
> > Signed-off-by: Sam James <sam@gentoo.org>
> > ---
> > Please consider this kind of a PoC for discussion. This came up on the
> > GCC bug tracker the other day which prompted me to post it and get people's
> > opinions. See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55212#c158.
>
> (Also, if we agree the idea is fine, I'll improve the commit message --
> it was just written out of exasperation for a local patchset when I was
> debugging something and going mad, sorry!)
>
> > libtool assumes that the warning output with vs without -fPIC is going
> > to be identical, hence the non-PIC build output should be completely suppressed.
> >
> > I think this is a premature optimization at best, and it's caused real
> > confusion to people. Can we drop it?
> >
> > If this looks OK, I can check more closely if I need to remove more
> > bits.
> >
> >   build-aux/ltmain.in | 2 --
> >   1 file changed, 2 deletions(-)
> >
> > diff --git a/build-aux/ltmain.in b/build-aux/ltmain.in
> > index 63377541..48e89042 100644
> > --- a/build-aux/ltmain.in
> > +++ b/build-aux/ltmain.in
> > @@ -1665,8 +1665,6 @@ compiler."
> >         func_append command " -o $obj"
> >         fi
> >   
> > -      # Suppress compiler output if we already did a PIC compilation.
> > -      func_append command "$suppress_output"
> >         func_show_eval_locale "$command" \
> >           '$opt_dry_run || $RM $removelist; exit $EXIT_FAILURE'
> >   
> >
> > base-commit: 22a7e547e9857fc94fe5bc7c921d9a4b49c09f8e

The patch seems incomplete, since I can only find one instance of
output suppression. If your patch is applied, the option to switch off
suppression should also be removed, but switching the logic around to
suppress if chosen seems like a better solution than complete removal.

However, you could also just specify '-no-suppress' when compiling
rather than changing the default behaviour.

--
Ileana Dumitrescu

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