[PATCH RFA] libstdc++: add more #if to std.cc (was Re: [Linaro-TCWG-CI] gcc-16-5581-g3ad2e2d707c3: 1 regression on arm)

[Jason Merrill]

On 12/6/25 11:52 AM, ci_notify@linaro.org wrote:
> Dear contributor,
> 
> Our automatic CI has detected problems related to your patch(es). Please find some details below.
> 
> In  arm-eabi v7-a softfp, after:
>    | commit gcc-16-5581-g3ad2e2d707c3
>    | Author: Jason Merrill <jason@redhat.com>
>    | Date:   Tue Nov 11 15:58:01 2025 +0530
>    |
>    |     driver/c++: add --compile-std-module
>    |
>    |     For simple testcases that want to use the std module, it would be useful to
>    |     have a reasonably short way to request building the binary module form
>    |     before the testcase.  So with this patch users can write
>    | ... 31 lines of the commit log omitted.
> 
> Produces 1 regression:
>    |
>    | regressions.sum:
>    | Running g++:g++.dg/modules/modules.exp ...
>    | FAIL: g++.dg/modules/compile-std1.C -std=c++26 (test for excess errors)

It seems that module std doesn't compile on arm-eabi, which is good to know.

There seem to be two general issues: first, that some of the <stdio.h> 
functions that <print> relies on aren't declared:

> /home/tcwg-buildslave/workspace/tcwg_gnu_1/abe/builds/x86_64-pc-linux-gnu/arm-eabi/gcc-gcc.git~master-sta\
> ge2/arm-eabi/libstdc++-v3/include/print: In member function 'virtual void std::__format::_File_sink::_M_o\
> verflow()':
> /home/tcwg-buildslave/workspace/tcwg_gnu_1/abe/builds/x86_64-pc-linux-gnu/arm-eabi/gcc-gcc.git~master-sta\
> ge2/arm-eabi/libstdc++-v3/include/print:197:20: error: '::fwrite_unlocked' has not been declared; did you\
>  mean '_fwrite_unlocked_r'?
> /home/tcwg-buildslave/workspace/tcwg_gnu_1/abe/builds/x86_64-pc-linux-gnu/arm-eabi/gcc-gcc.git~master-sta\
> ge2/arm-eabi/libstdc++-v3/include/print: In constructor 'std::__format::_File_sink::_File_sink(FILE*, boo\
> l)':
> /home/tcwg-buildslave/workspace/tcwg_gnu_1/abe/builds/x86_64-pc-linux-gnu/arm-eabi/gcc-gcc.git~master-sta\
> ge2/arm-eabi/libstdc++-v3/include/print:212:9: error: '::flockfile' has not been declared; did you mean '\
> _flockfile'?
> /home/tcwg-buildslave/workspace/tcwg_gnu_1/abe/builds/x86_64-pc-linux-gnu/arm-eabi/gcc-gcc.git~master-sta\
> ge2/arm-eabi/libstdc++-v3/include/print: In destructor 'std::__format::_File_sink::~_File_sink()':
> /home/tcwg-buildslave/workspace/tcwg_gnu_1/abe/builds/x86_64-pc-linux-gnu/arm-eabi/gcc-gcc.git~master-sta\
> ge2/arm-eabi/libstdc++-v3/include/print:218:11: error: '::putc_unlocked' has not been declared; did you m\
> ean '_putc_unlocked_r'?
> /home/tcwg-buildslave/workspace/tcwg_gnu_1/abe/builds/x86_64-pc-linux-gnu/arm-eabi/gcc-gcc.git~master-sta\
> ge2/arm-eabi/libstdc++-v3/include/print:219:9: error: '::funlockfile' has not been declared; did you mean\
>  '_funlockfile'?

It seems that newlib doesn't declare these functions under -std=c++26, 
only -std=gnu++26.  I don't know what the right approach to this is.

and then a bunch of "not declared" exports, such as

> /home/tcwg-buildslave/workspace/tcwg_gnu_1/abe/builds/x86_64-pc-linux-gnu/arm-eabi/gcc-gcc.git~master-sta\
> ge2/arm-eabi/libstdc++-v3/include/bits/std.cc:1002:14: error: 'condition_variable' has not been declared \
> in 'std'

This looks like just needing to add more #if to std.cc, as below.  OK 
for trunk?

Incidentally, is it expected that arm-eabi doesn't support gthread?

Jason
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