Using std::locale fails to link fmt 12 on Arch Linux with clang

[jordan-woyak]

The follow program fails to link on Arch Linux with clang++.
g++ links as expected.

I think this is somewhat similar to issue #2794.

// Enabling this allows the program to always link.
//#define FMT_HEADER_ONLY

#include <cstdio>
#include <ctime>
#include <locale>

#include <fmt/chrono.h>
#include <fmt/format.h>

int main()
{
    std::puts(fmt::format(std::locale(""), "{:L%c}", fmt::gmtime(std::time_t{})).c_str());
}

clang++ fmt-link-fail.cpp -lfmt

fmt-link-fail.cpp:(.text+0x41): undefined reference to `_ZN3fmt3v1210locale_refC1ISt6localeTnNSt9enable_ifIXneszsrT_7collateLi0EEiE4typeELi0EEERKS5_'

I'm reaching the limits of my linker understanding here.

Is this supposed to work?
If the ABI is not compatible can I somehow detect this and automatically define FMT_HEADER_ONLY ?

[vitaut]

Thanks for reporting, we should definitely make this work.

The symbol in question should normally be defined via

fmt/src/format.cc

Line 13 in 8eebb43

template FMT_API locale_ref::locale_ref(const std::locale& loc);

but I guess there is some incompatibility between clang and gcc. Could you post the list of symbols exported from the library that contain locale_ref in them?

[vitaut]

godbolt repro: https://www.godbolt.org/z/3MvEs3Tb8

[vitaut]

Related to llvm/llvm-project#85656.

[Arghnews]

Also as noted in one of the related comments on a related issue, using -fclang-abi-compat=17 with clang does seem to fix it for this case - but not sure if necessarily all cases - ie. it makes the mangled symbols match for the minimal example provided: https://www.godbolt.org/z/o9en3Yq43 So it may have suitability as a workaround

I was passing by, here's gcc 13 and clang 18 output from fmt head then filtered with nm --defined-only libfmt.a | grep -i locale_ref

gcc:

0000000000000000 W _ZN3fmt3v1210locale_refC1ISt6localeLi0EEERKT_
0000000000000000 W _ZN3fmt3v1210locale_refC2ISt6localeLi0EEERKT_
0000000000000000 n _ZN3fmt3v1210locale_refC5ISt6localeLi0EEERKT_
0000000000005450 T _ZN3fmt3v126detail10vformat_toERNS1_6bufferIcEENS0_17basic_string_viewIcEENS0_17basic_format_argsINS0_7contextEEENS0_10locale_refE
000000000000048d t _ZN3fmt3v126detail10vformat_toERNS1_6bufferIcEENS0_17basic_string_viewIcEENS0_17basic_format_argsINS0_7contextEEENS0_10locale_refE.cold
0000000000000000 W _ZN3fmt3v126detail11write_fixedIcNS1_14digit_groupingIcEENS0_14basic_appenderIcEENS1_14big_decimal_fpEEET1_S8_RKT2_iT_RKNS0_12format_specsENS0_4signENS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail11write_fixedIcNS1_14digit_groupingIcEENS0_14basic_appenderIcEENS1_9dragonbox10decimal_fpIdEEEET1_SA_RKT2_iT_RKNS0_12format_specsENS0_4signENS0_10locale_refE
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0000000000000000 W _ZN3fmt3v126detail14digit_groupingIcEC1ENS0_10locale_refEb
0000000000000000 W _ZN3fmt3v126detail14digit_groupingIcEC2ENS0_10locale_refEb
0000000000000000 n _ZN3fmt3v126detail14digit_groupingIcEC5ENS0_10locale_refEb
0000000000000000 W _ZN3fmt3v126detail14do_write_floatIcNS1_14digit_groupingIcEENS0_14basic_appenderIcEENS1_14big_decimal_fpEEET1_S8_RKT2_RKNS0_12format_specsENS0_4signEiNS0_10locale_refE
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0000000000000000 W _ZN3fmt3v126detail18decimal_point_implIcEET_NS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail18decimal_point_implIwEET_NS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail18thousands_sep_implIcEENS1_20thousands_sep_resultIT_EENS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail18thousands_sep_implIwEENS1_20thousands_sep_resultIT_EENS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail5writeIcNS0_14basic_appenderIcEEeLi0EEET0_S5_T1_NS0_12format_specsENS0_10locale_refE
0000000000005200 T _ZN3fmt3v126detail9write_locENS0_14basic_appenderIcEENS0_9loc_valueERKNS0_12format_specsENS0_10locale_refE
0000000000000461 t _ZN3fmt3v126detail9write_locENS0_14basic_appenderIcEENS0_9loc_valueERKNS0_12format_specsENS0_10locale_refE.cold
0000000000000000 W _ZNK3fmt3v1210locale_ref3getISt6localeEET_v

clang:

0000000000000000 W _ZN3fmt3v1210locale_refC1ISt6localeTnNSt9enable_ifIXneszsrT_7collateLi0EEiE4typeELi0EEERKS5_
0000000000000000 W _ZN3fmt3v1210locale_refC2ISt6localeTnNSt9enable_ifIXneszsrT_7collateLi0EEiE4typeELi0EEERKS5_
0000000000000000 n _ZN3fmt3v1210locale_refC5ISt6localeTnNSt9enable_ifIXneszsrT_7collateLi0EEiE4typeELi0EEERKS5_
0000000000000ba0 T _ZN3fmt3v126detail10vformat_toERNS1_6bufferIcEENS0_17basic_string_viewIcEENS0_17basic_format_argsINS0_7contextEEENS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail11write_fixedIcNS1_14digit_groupingIcEENS0_14basic_appenderIcEENS1_14big_decimal_fpEEET1_S8_RKT2_iT_RKNS0_12format_specsENS0_4signENS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail11write_fixedIcNS1_14digit_groupingIcEENS0_14basic_appenderIcEENS1_9dragonbox10decimal_fpIdEEEET1_SA_RKT2_iT_RKNS0_12format_specsENS0_4signENS0_10locale_refE
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0000000000000000 W _ZN3fmt3v126detail14digit_groupingIcEC2ENS0_10locale_refEb
0000000000000000 W _ZN3fmt3v126detail14do_write_floatIcNS1_14digit_groupingIcEENS0_14basic_appenderIcEENS1_14big_decimal_fpEEET1_S8_RKT2_RKNS0_12format_specsENS0_4signEiNS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail14do_write_floatIcNS1_14digit_groupingIcEENS0_14basic_appenderIcEENS1_9dragonbox10decimal_fpIdEEEET1_SA_RKT2_RKNS0_12format_specsENS0_4signEiNS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail14do_write_floatIcNS1_14digit_groupingIcEENS0_14basic_appenderIcEENS1_9dragonbox10decimal_fpIfEEEET1_SA_RKT2_RKNS0_12format_specsENS0_4signEiNS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail18decimal_point_implIcEET_NS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail18decimal_point_implIwEET_NS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail18thousands_sep_implIcEENS1_20thousands_sep_resultIT_EENS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail18thousands_sep_implIwEENS1_20thousands_sep_resultIT_EENS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail5writeIcNS0_14basic_appenderIcEEdTnNSt9enable_ifIXsr17is_floating_pointIT1_EE5valueEiE4typeELi0EEET0_S9_S6_NS0_12format_specsENS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail5writeIcNS0_14basic_appenderIcEEEET0_S5_T_RKNS0_12format_specsENS0_10locale_refE
0000000000000000 W _ZN3fmt3v126detail5writeIcNS0_14basic_appenderIcEEeTnNSt9enable_ifIXsr17is_floating_pointIT1_EE5valueEiE4typeELi0EEET0_S9_S6_NS0_12format_specsENS0_10locale_refE
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0000000000000180 T _ZN3fmt3v126detail9write_locENS0_14basic_appenderIcEENS0_9loc_valueERKNS0_12format_specsENS0_10locale_refE
0000000000000000 W _ZNK3fmt3v1210locale_ref3getISt6localeEET_v
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0000000000000000 W _ZZN3fmt3v126detail14do_write_floatIcNS1_14digit_groupingIcEENS0_14basic_appenderIcEENS1_9dragonbox10decimal_fpIdEEEET1_SA_RKT2_RKNS0_12format_specsENS0_4signEiNS0_10locale_refEENKUlS6_E_clES6_
0000000000000000 W _ZZN3fmt3v126detail14do_write_floatIcNS1_14digit_groupingIcEENS0_14basic_appenderIcEENS1_9dragonbox10decimal_fpIfEEEET1_SA_RKT2_RKNS0_12format_specsENS0_4signEiNS0_10locale_refEENKUlS6_E_clES6_

[vitaut]

Tenative fix: 6570bc2. @jordan-woyak, could you confirm that it resolves the issue?

[jordan-woyak]

Tenative fix: 6570bc2. @jordan-woyak, could you confirm that it resolves the issue?

This unfortunately does not seem to fix the linker error.

If I build 45247c8 with g++ and try to link it with my above test program built with clang++ I still get:

undefined reference to `_ZN3fmt3v1210locale_refC1ISt6localeTnNSt9enable_ifIXneszsrT_7collateLi0EEiE4typeELi0EEERKS5_'

Building 45247c8 with clang++ works around the error as expected.

[vitaut]

A small follow-up that should make the mangling consistent: 9721d97.

[jordan-woyak]

A small follow-up that should make the mangling consistent: 9721d97.

This is worse :P

Mismatching g++/clang++ produces the same:

undefined reference to `_ZN3fmt3v1210locale_refC1ISt6localeTnNSt9enable_ifIXneszsrT_7collateLi0EEiE4typeELi0EEERKS5_'

Matching g++/clang++ now also doesn't link:

undefined reference to `fmt::v12::locale_ref::locale_ref<std::locale, 0>(std::locale const&)'

[vitaut]

Ah, the value of std::locale::collate is implementation-defined so ABI incompatibility is now replaced with standard library incompatibility =).

[vitaut]

Take 3: 9395ef5.

[jordan-woyak]

Take 3: 9395ef5.

Building everything with g++ works per usual.

If I build fmt with g++ and the test program with clang++ I get the same existing linker error:

_ZN3fmt3v1210locale_refC1ISt6localeTnNSt9enable_ifIXneszsrT_7collateLi0EEiE4typeELi0EEERKS5_

But now if I build fmt with clang++, building my test program (with default options) only links properly with g++.

Using clang++ for everything now produces the linker error.

Edit: Hold on, I'm probably not using the updated headers in the test program...

[jordan-woyak]

Sorry, you can ignore a lot of what I said. If I actually use the updated headers for the test program then 45247c8 9721d97 and 9395ef5 and even latest master work with mismatched g++/clang++.

[vitaut]

No worries and thanks for testing. I merged in a somewhat more resilient to ABI differences version of SFINAE check and closing this.

[vitaut]

Thinking more of it, since 45247c8 fixes the issue and does not introduce an ABI break for clang, let's go back to it.