Re: [PATCH] Do not prepend target triple to -fuse-ld=lld,mold.

[Richard Biener <rguenther@suse.de>]

On Tue, 7 Nov 2023, Tatsuyuki Ishi wrote:

> > On Oct 16, 2023, at 18:16, Richard Biener <rguenther@suse.de> wrote:
> > 
> > On Mon, 16 Oct 2023, Tatsuyuki Ishi wrote:
> > 
> >> 
> >> 
> >>> On Oct 16, 2023, at 17:55, Richard Biener <rguenther@suse.de> wrote:
> >>> 
> >>> On Mon, 16 Oct 2023, Tatsuyuki Ishi wrote:
> >>> 
> >>>> 
> >>>> 
> >>>>> On Oct 16, 2023, at 17:39, Richard Biener <rguenther@suse.de> wrote:
> >>>>> 
> >>>>> On Mon, 16 Oct 2023, Tatsuyuki Ishi wrote:
> >>>>> 
> >>>>>> lld and mold are platform-agnostic and not prefixed with target triple.
> >>>>>> Prepending the target triple makes it less likely to find the intended
> >>>>>> linker executable.
> >>>>>> 
> >>>>>> A potential breaking change is that we no longer try to search for
> >>>>>> triple-prefixed lld/mold binaries anymore. However, since there doesn't
> >>>>>> seem to be support to build LLVM or mold with triple-prefixed executable
> >>>>>> names, it seems better to just not bother with that case.
> >>>>>> 
> >>>>>> 	PR driver/111605
> >>>>>> 
> >>>>>> gcc/Changelog:
> >>>>>> 
> >>>>>> 	* collect2.cc (main): Do not prepend target triple to
> >>>>>> 	-fuse-ld=lld,mold.
> >>>>>> ---
> >>>>>> gcc/collect2.cc | 13 ++++++++-----
> >>>>>> 1 file changed, 8 insertions(+), 5 deletions(-)
> >>>>>> 
> >>>>>> diff --git a/gcc/collect2.cc b/gcc/collect2.cc
> >>>>>> index 63b9a0c233a..c943f9f577c 100644
> >>>>>> --- a/gcc/collect2.cc
> >>>>>> +++ b/gcc/collect2.cc
> >>>>>> @@ -865,12 +865,15 @@ main (int argc, char **argv)
> >>>>>> int i;
> >>>>>> 
> >>>>>> for (i = 0; i < USE_LD_MAX; i++)
> >>>>>> -    full_ld_suffixes[i]
> >>>>>> #ifdef CROSS_DIRECTORY_STRUCTURE
> >>>>>> -      = concat (target_machine, "-", ld_suffixes[i], NULL);
> >>>>>> -#else
> >>>>>> -      = ld_suffixes[i];
> >>>>>> -#endif
> >>>>>> +    /* lld and mold are platform-agnostic and not prefixed with target
> >>>>>> +       triple.  */
> >>>>>> +    if (!(i == USE_LLD_LD || i == USE_MOLD_LD))
> >>>>>> +      full_ld_suffixes[i] = concat (target_machine, "-", ld_suffixes[i],
> >>>>>> +				    NULL);
> >>>>>> +    else
> >>>>>> +#endif
> >>>>>> +      full_ld_suffixes[i] = ld_suffixes[i];
> >>>>>> 
> >>>>>> p = argv[0] + strlen (argv[0]);
> >>>>>> while (p != argv[0] && !IS_DIR_SEPARATOR (p[-1]))
> >>>>> 
> >>>>> Since we later do
> >>>>> 
> >>>>> /* Search the compiler directories for `ld'.  We have protection against
> >>>>>   recursive calls in find_a_file.  */
> >>>>> if (ld_file_name == 0)
> >>>>>  ld_file_name = find_a_file (&cpath, ld_suffixes[selected_linker], 
> >>>>> X_OK);
> >>>>> /* Search the ordinary system bin directories
> >>>>>   for `ld' (if native linking) or `TARGET-ld' (if cross).  */
> >>>>> if (ld_file_name == 0)
> >>>>>  ld_file_name = find_a_file (&path, full_ld_suffixes[selected_linker], 
> >>>>> X_OK);
> >>>>> 
> >>>>> I wonder how having full_ld_suffixes[LLD|MOLD] == ld_suffixes[LLD|MOLD]
> >>>>> fixes anything?
> >>>> 
> >>>> Per the linked PR, the intended use case for this is when one wants to use their system lld/mold with a separately packaged cross toolchain, without requiring them to symlink their system lld/mold into the cross toolchain bin directory.
> >>>> 
> >>>> (Note that the first search is against COMPILER_PATH while the latter is 
> >>>> against PATH).
> >>> 
> >>> Ah.  So what about instead adding here
> >>> 
> >>>  /* Search the ordinary system bin directories for mold/lld even in
> >>>     a cross configuration.  */
> >>>  if (ld_file_name == 0
> >>>      && selected_linker == ...)
> >>>    ld_file_name = find_a_file (&path, ld_suffixes[selected_linker], X_OK);
> >>> 
> >>> instead?  That would keep things working in case the user has a
> >>> xyz-arch-mold in the system dir but uses GNU ld on the host
> >>> otherwise, lacking a 'mold' binary there?
> >>> 
> >>> That is, we'd only add, not change what we search for.
> >> 
> >> I considered that, but as described in commit message, it doesn?t seem anyone has created stuff named xyz-arch-lld or xyz-arch-mold. Closest is Gentoo?s symlink mentioned in this thread, but that?s xyz-arch-ld -> ld.lld/mold.
> >> As such, this feels like a quirk, not something we need to keep compatibility for.
> > 
> > I don't have a good idea whether this is the case or not unfortunately
> > so if it's my call I would err on the safe side.
> > 
> > We seem to recognize mold and lld only since GCC 12 which both are
> > still maintained so I think we might want to do the change on all
> > those branches?
> > 
> > If you feel confident there's indeed no such installs then let's go
> > with your original patch.
> > 
> > Thus, OK for trunk and the affected branches after a while of no
> > reported issues.
> 
> Hi,
> 
> Can I consider this an approval for this patch to be applied to trunk?

Yes.

> I would appreciate if this patch could be tested in GCC 14 prereleases.
> 
> I suppose backporting after no reported issues in GCC 14 would be the plan here?
> 
> Please let me know in case of misunderstandings.

You understood correctly.

Richard.

> Thanks,
> Tatsuyuki.
> 
> > Thanks,
> > Richard.
> > 
> >> The proposed change seems simple enough though, so if you consider this 
> >> a compatibility issue I can go for that way as well.
> > 
> >> Tatsuyuki.
> >> 
> >>> 
> >>> Thanks,
> >>> Richard.
> >> 
> >> 
> > 
> > -- 
> > Richard Biener <rguenther@suse.de <mailto:rguenther@suse.de>>
> > SUSE Software Solutions Germany GmbH,
> > Frankenstrasse 146, 90461 Nuernberg, Germany;
> > GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)