Re: [PATCH][_GLIBCXX_INLINE_VERSION] Adapt to_chars/from_chars symbols

["François Dumont" <frs.dumont@gmail.com>]

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On 28/11/22 11:21, Jonathan Wakely wrote:
>
>
> On Mon, 28 Nov 2022 at 10:10, Jonathan Wakely <jwakely@redhat.com> wrote:
>
>
>
>     On Mon, 28 Nov 2022 at 06:07, François Dumont via Libstdc++
>     <libstdc++@gcc.gnu.org <mailto:libstdc%2B%2B@gcc.gnu.org>> wrote:
>
>         This patch is fixing those tests:
>
>         20_util/to_chars/float128_c++23.cc
>         std/format/formatter/requirements.cc
>         std/format/functions/format.cc
>         std/format/functions/format_to_n.cc
>         std/format/functions/size.cc
>         std/format/functions/vformat_to.cc
>         std/format/string.cc
>
>         Note that symbols used in <format> for __ibm128 and __iee128
>         are untested.
>
>         I even wonder if the normal mode ones are because I cannot
>         find the
>         symbols used in gnu.ver.
>
>
>              libstdc++: [_GLIBCXX_INLINE_VERSION] Add to_chars/from_chars
>         symbols export
>
>              libstdc++-v3/ChangeLog
>
>                      * include/std/format
>         [_GLIBCXX_INLINE_VERSION](to_chars):
>         Adapt __asm symbol
>                      specifications.
>                      * config/abi/pre/gnu-versioned-namespace.ver: Add
>         to_chars/from_chars symbols
>                      export.
>
>         Ok to commit ?
>
>
>
>     Why are changes needed to the linker script?
>
>     Those functions should already match the general wildcard:
>
>         # Names inside the 'extern' block are demangled names.
>         extern "C++"
>         {
>           std::*;
>           std::__8::*;
>         };
>
>
>
No idear, my guess was that it has something to do with the __asm usages 
in <format> and with the commnt:

   // These overloads exist in the library, but are not declared for C++20.
   // Make them available as std::__format::to_chars.

Maybe they exist in the library but are unused so not exported unless 
specified in the linker script ?


>
> Instead of nine separate #if blocks, can we just do:
>
> #if _GLIBCXX_INLINE_VERSION
> # define _GLIBCXX_ALIAS(S) __asm("_ZNSt3__8" S)
> #else
> # define _GLIBCXX_ALIAS(S) __asm("_ZNSt" S)
> #endif
>
>  And then use:
>
>   _GLIBCXX_ALIAS("8to_charsPcS_eSt12chars_format");
>
> and finally:
>
> #undef _GLIBCXX_ALIAS
>
>
I tried and as expected it's not working because the diff in the symbol 
is not limited to the '3__8' pattern. 'chars_format' is also defined in 
versioned namespace which might perhaps explain some mangling diff.

Here is an updated patch though, I had forgotten to replace a _DF128 
with a __ieee128 in the untested part of this patch.

If you prefer to take a closer look later I'll just re-submit my patch 
to move versioned namespace mode to cxx11 abi knowing that those tests 
are already FAIL.

François