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 17:39, 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).

Tatsuyuki.

> 
> Richard.