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

[Richard Biener <rguenther@suse.de>]

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.

Thanks,
Richard.