On Wed, 3 May 2023 at 19:55, Jakub Jelinek via Libstdc++
<libstd...@gcc.gnu.org> wrote:
>
> Hi!
>
> This is an ABI problem on powerpc64le-linux, introduced in 13.1.
> When libstdc++ is configured against old glibc, the
> _ZSt10from_charsPKcS0_RDF128_St12chars_format@@GLIBCXX_3.4.31
> _ZSt8to_charsPcS_DF128_@@GLIBCXX_3.4.31
> _ZSt8to_charsPcS_DF128_St12chars_format@@GLIBCXX_3.4.31
> _ZSt8to_charsPcS_DF128_St12chars_formati@@GLIBCXX_3.4.31
> symbols are exported from the library, while when it is configured against
> new enough glibc, those symbols aren't exported and we export instead
> _ZSt10from_charsPKcS0_Ru9__ieee128St12chars_format@@GLIBCXX_IEEE128_3.4.29
> _ZSt8to_charsPcS_u9__ieee128@@GLIBCXX_IEEE128_3.4.29
> _ZSt8to_charsPcS_u9__ieee128St12chars_format@@GLIBCXX_IEEE128_3.4.29
> _ZSt8to_charsPcS_u9__ieee128St12chars_formati@@GLIBCXX_IEEE128_3.4.29
> together with various other @@GLIBCXX_IEEE128_3.4.{29,30,31} and
> @@CXXABI_IEEE128_1.3.13 symbols. The idea was that those *IEEE128* symbol
> versions (similarly to *LDBL* symbol versions) are optional (but if it
> appears, all symbols from it up to the version of the library appears),
> but the base appears always.
> My _Float128 from_chars/to_chars changes unfortunately broke this.
> I believe nothing really uses those symbols if libstdc++ has been
> configured against old glibc, so if 13.1 wasn't already released, it might
> be best to make sure they aren't exported on powerpc64le-linux.
> But as they were exported, I think the best resolution for this ABI
> difference is to add those 4 symbols as aliases to the
> GLIBCXX_IEEE128_3.4.29 *u9__ieee128* symbols, which the following patch
> does.
>
> Tested on powerpc64le-linux (both configured against glibc 2.36 and 2.17)
> and powerpc64-linux (configured against glibc 2.17), ok for trunk?
Do we want a #pragma to suppress -Wattribute-alias here?
>
> 2023-05-03 Jakub Jelinek <ja...@redhat.com>
>
> * src/c++17/floating_from_chars.cc
> (_ZSt10from_charsPKcS0_RDF128_St12chars_format): New alias to
> _ZSt10from_charsPKcS0_Ru9__ieee128St12chars_format.
> * src/c++17/floating_to_chars.cc (_ZSt8to_charsPcS_DF128_): New alias
> to
> _ZSt8to_charsPcS_u9__ieee128.
> (_ZSt8to_charsPcS_DF128_St12chars_format): New alias to
> _ZSt8to_charsPcS_u9__ieee128St12chars_format.
> (_ZSt8to_charsPcS_DF128_St12chars_formati): New alias to
> _ZSt8to_charsPcS_u9__ieee128St12chars_formati.
> * config/abi/post/powerpc64le-linux-gnu/baseline_symbols.txt: Updated.
>
> --- libstdc++-v3/src/c++17/floating_from_chars.cc.jj 2023-04-13
> 23:00:36.125459347 +0200
> +++ libstdc++-v3/src/c++17/floating_from_chars.cc 2023-05-03
> 17:24:45.121600206 +0200
> @@ -1272,6 +1272,13 @@ from_chars(const char* first, const char
> // fast_float doesn't support IEEE binary128 format, but we can use
> strtold.
> return from_chars_strtod(first, last, value, fmt);
> }
> +
> +extern "C" from_chars_result
> +_ZSt10from_charsPKcS0_RDF128_St12chars_format(const char* first,
> + const char* last,
> + __ieee128& value,
> + chars_format fmt) noexcept
> +__attribute__((alias
> ("_ZSt10from_charsPKcS0_Ru9__ieee128St12chars_format")));
> #elif defined(USE_STRTOF128_FOR_FROM_CHARS)
> from_chars_result
> from_chars(const char* first, const char* last, _Float128& value,
> --- libstdc++-v3/src/c++17/floating_to_chars.cc.jj 2023-01-16
> 23:19:06.284716774 +0100
> +++ libstdc++-v3/src/c++17/floating_to_chars.cc 2023-05-03 17:12:16.766877278
> +0200
> @@ -1851,6 +1851,23 @@ to_chars(char* first, char* last, __floa
> {
> return __floating_to_chars_precision(first, last, value, fmt, precision);
> }
> +
> +extern "C" to_chars_result
> +_ZSt8to_charsPcS_DF128_(char* first, char* last, __float128 value) noexcept
> + __attribute__((alias ("_ZSt8to_charsPcS_u9__ieee128")));
> +
> +extern "C" to_chars_result
> +_ZSt8to_charsPcS_DF128_St12chars_format(char* first, char* last,
> + __float128 value,
> + chars_format fmt) noexcept
> + __attribute__((alias ("_ZSt8to_charsPcS_u9__ieee128St12chars_format")));
> +
> +extern "C" to_chars_result
> +_ZSt8to_charsPcS_DF128_St12chars_formati(char* first, char* last,
> + __float128 value,
> + chars_format fmt,
> + int precision) noexcept
> + __attribute__((alias ("_ZSt8to_charsPcS_u9__ieee128St12chars_formati")));
> #else
> to_chars_result
> to_chars(char* first, char* last, _Float128 value) noexcept
> ---
> libstdc++-v3/config/abi/post/powerpc64le-linux-gnu/baseline_symbols.txt.jj
> 2023-05-02 19:27:47.538504941 +0200
> +++ libstdc++-v3/config/abi/post/powerpc64le-linux-gnu/baseline_symbols.txt
> 2023-05-03 19:06:33.389469841 +0200
> @@ -4491,6 +4491,7 @@ FUNC:_ZNSt9type_infoD1Ev@@GLIBCXX_3.4
> FUNC:_ZNSt9type_infoD2Ev@@GLIBCXX_3.4
>
> FUNC:_ZNVSt9__atomic011atomic_flag12test_and_setESt12memory_order@@GLIBCXX_3.4.11
> FUNC:_ZNVSt9__atomic011atomic_flag5clearESt12memory_order@@GLIBCXX_3.4.11
> +FUNC:_ZSt10from_charsPKcS0_RDF128_St12chars_format@@GLIBCXX_3.4.31
> FUNC:_ZSt10from_charsPKcS0_RdSt12chars_format@@GLIBCXX_3.4.29
> FUNC:_ZSt10from_charsPKcS0_ReSt12chars_format@@GLIBCXX_3.4.29
> FUNC:_ZSt10from_charsPKcS0_RfSt12chars_format@@GLIBCXX_3.4.29
> @@ -4641,6 +4642,9 @@ FUNC:_ZSt7getlineIwSt11char_traitsIwESaI
>
> FUNC:_ZSt7getlineIwSt11char_traitsIwESaIwEERSt13basic_istreamIT_T0_ES7_RNSt7__cxx1112basic_stringIS4_S5_T1_EES4_@@GLIBCXX_3.4.21
>
> FUNC:_ZSt7getlineIwSt11char_traitsIwESaIwEERSt13basic_istreamIT_T0_ES7_RSbIS4_S5_T1_E@@GLIBCXX_3.4
>
> FUNC:_ZSt7getlineIwSt11char_traitsIwESaIwEERSt13basic_istreamIT_T0_ES7_RSbIS4_S5_T1_ES4_@@GLIBCXX_3.4
> +FUNC:_ZSt8to_charsPcS_DF128_@@GLIBCXX_3.4.31
> +FUNC:_ZSt8to_charsPcS_DF128_St12chars_format@@GLIBCXX_3.4.31
> +FUNC:_ZSt8to_charsPcS_DF128_St12chars_formati@@GLIBCXX_3.4.31
> FUNC:_ZSt8to_charsPcS_d@@GLIBCXX_3.4.29
> FUNC:_ZSt8to_charsPcS_dSt12chars_format@@GLIBCXX_3.4.29
> FUNC:_ZSt8to_charsPcS_dSt12chars_formati@@GLIBCXX_3.4.29
>
> Jakub
>
