[build, lto] Only accept -fuse-linker-plugin if linker supports -plugin (PR lto/46944)

[Rainer Orth]

Hi Ralf,

it's been a week since I answered your questions on this patch.  Could
you please have a look?

Thanks.
        Rainer


>>> I haven't found if there are provisions for in-tree gold, though, and
>>> still cannot test that.
>>
>> I'm not quite sure I understand this statement.  I built a combined tree
>> with gold enabled a while ago (must've been several months now).
>> I might be misunderstanding this.
>
> I suppose I've been unclear: I'm specificially referring to the current
> code for setting gcc_cv_lto_plugin: in the in-tree case, there's nothing
> that deals with in-tree gold.
>
>>>    if test $in_tree_ld = yes -a x"$ORIGINAL_PLUGIN_LD_FOR_TARGET" = x"$gcc_cv_ld"; then
>>> -    if test "$gcc_cv_gld_major_version" -eq 2 -a "$gcc_cv_gld_minor_version" -ge 21 -o "$gcc_cv_gld_major_version" -gt 2; then
>>> -      gcc_cv_lto_plugin=2
>>> -    elif test "$ld_is_gold" = yes -a "$gcc_cv_gld_major_version" -eq 2 -a "$gcc_cv_gld_minor_version" -eq 20; then
>>> -      gcc_cv_lto_plugin=1
>>> -
>>> +    ld_ver="GNU ld"
>>> +    # FIXME: ld_is_gold?
>>
>> What about this FIXME?  Did you test gold?  Is it not relevant here?
>> Can the FIXME go?
>
> I cannot test gold since it doesn't yet work on Solaris: cf. binutils PR
> gold/12525.  We made some progress on that front, but the PR is
> currently stalled and I had other things on my plate that prevented me
> from pushing it.  As I said, the current code (before my patch) doesn't
> handle in-tree gold, so I don't feel obliged to change that, especially
> since I'm in no good position to test.
>
>>> +      ld_vers_major=`expr "$ld_vers" : '\([0-9]*\)'`
>>> +      ld_vers_minor=`expr "$ld_vers" : '[0-9]*\.\([0-9]*\)'`
>>
>> Can you try the expr statements quickly on Tru64?  If not, I can do it
>> for you ('info Autoconf --index expr' is long and tells of many woes).
>
> I just tried with /bin/expr and ld_vers set to 2.20.1.  OTOH, this isn't
> relevant for two reasons: this code is identical to the one determining
> ld_vers_major/ld_vers_minor further up in gcc/configure.ac, and GNU ld
> (as well as GNU as) aren't currently supported on Tru64 UNIX and I
> seriously doubt that will change over the remaining livetime of the
> platform.
>
>> Thanks, and sorry for the delay,
>
> No worries.  I'd just like to get this series of patches out of my queue
> (and eventually backported to the 4.6 branch if all issues are sorted
> out).  Maybe one of the build maintainers finds some time to handle the
> current mess that are the linker tests in gcc/configure.ac, compared to
> what we do for the assembler.
>
> Thanks.
> 	Rainer

-- 
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Rainer Orth, Center for Biotechnology, Bielefeld University