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

[Tatsuyuki Ishi <ishitatsuyuki@gmail.com>]

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> 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.

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.