[v3 PATCH] Implement LWG 2221, No formatted output operator for nullptr

Rainer Orth ro@CeBiTec.Uni-Bielefeld.DE
Fri Jan 11 09:07:00 GMT 2019


Hi Jonathan,

>>this patch broke Solaris bootstrap:
>>
>>ld: fatal: libstdc++-symbols.ver-sun: 7117: symbol 'std::basic_ostream<char, std::char_traits<char> >::operator<<(decltype(nullptr))': symbol version conflict
>>ld: fatal: libstdc++-symbols.ver-sun: 7119: symbol 'std::basic_ostream<wchar_t, std::char_traits<wchar_t> >::operator<<(decltype(nullptr))': symbol version conflict
>>
>>ld: fatal: libstdc++-symbols.ver-sun: 7117: symbol '_ZNSolsEDn': symbol version conflict
>>ld: fatal: libstdc++-symbols.ver-sun: 7119: symbol '_ZNSt13basic_ostreamIwSt11char_traitsIwEElsEDn': symbol version conflict
>>
>>Again, there were two matches for those two symbols:
>>
>>  GLIBCXX_3.4
>>    ##_ZNSolsE*[^Dg] (glob)
>>    _ZNSolsEDn;
>>  GLIBCXX_3.4.26
>>    ##_ZNSolsEDn (glob)
>>    _ZNSolsEDn;
>>
>>  GLIBCXX_3.4
>>    ##_ZNSt13basic_ostreamIwSt11char_traitsIwEElsE*[^Dg] (glob)
>>    _ZNSt13basic_ostreamIwSt11char_traitsIwEElsEDn;
>>  GLIBCXX_3.4.26
>>    ##_ZNSt13basic_ostreamIwSt11char_traitsIwEElsEDn (glob)
>>    _ZNSt13basic_ostreamIwSt11char_traitsIwEElsEDn;
>>
>>ISTM that the patterns were backwards.  The following patch fixes this
>>and allowed i386-pc-solaris2.11 bootstrap to complete without
>>regressions relative to the last successful one.
>
> I think what I should have done is change [^g] to [^gn]. That
> preserves the original behaviour (don't match the ppc64 long double
> symbols) but also excludes the new symbols, which end in 'n'.
>
> Maybe the attached patch would be better though. It matches every
> basic_ostream::operator<<(T) for any scalar T except 'g', and adds a
> second pattern to match basic_ostream::operator<<(T*) for various T.
> But neither of those matches the new operator<<(nullptr_t) overload.

it allowed me to link libstdc++.so, too.  For my patch I'd only been
going from the ld errors and the matching patterns in the generated
libstdc++.map-sun, not knowing the background here.

> FWIW I did run my symbol checker script, but it gets lots of false
> positives because it doesn't understand the #if preprocessor
> conditions, so it sees lots of false positive duplicates. I need to
> make it smarter for it to be useful here.

Indeed: the variation possible here can be a total PITA ;-)

Thanks.
        Rainer

-- 
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Rainer Orth, Center for Biotechnology, Bielefeld University



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