[RFA] libstdc++: add more #if to std.cc (was Re: [Linaro-TCWG-CI] gcc-16-5581-g3ad2e2d707c3: 1 regression on arm)
Commit Message
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
Comments
On Sat, 6 Dec 2025 at 09:14, Jason Merrill <jason@redhat.com> wrote:
>
> 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?
OK
I keep going back and forth on whether we should provide dumb no-op
versions of std::mutex etc. for non-ghtreads targets, so that the
types exist they just don't do anything. We provide std::thread for
non-gthreads, but it only has a default constructor, so you can't
actually create new threads of execution with it.
And for this one we could just define the thread-safe pool as an alias
of the unsynchronized pool for non-gthreads:
+#if _GLIBCXX_HAS_GTHREADS
using std::pmr::synchronized_pool_resource;
+#endif
using std::pmr::unsynchronized_pool_resource;
>
> Incidentally, is it expected that arm-eabi doesn't support gthread?
>
> Jason
From e098c651d9269e8ddb36dbf43cfe1876f5f40168 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Sat, 6 Dec 2025 15:55:43 +0800
Subject: [PATCH] libstdc++: add more #if to std.cc
To: gcc-patches@gcc.gnu.org
compile-std1.C was breaking on arm-eabi because these interfaces aren't
declared. So for exporting let's check the same macros that control
declaring them.
libstdc++-v3/ChangeLog:
* src/c++23/std.cc.in: Add more #if.
---
libstdc++-v3/src/c++23/std.cc.in | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)
@@ -573,14 +573,20 @@ export namespace std
using std::atomic_flag;
using std::atomic_flag_clear;
using std::atomic_flag_clear_explicit;
+#if __cpp_lib_atomic_wait
using std::atomic_flag_notify_all;
using std::atomic_flag_notify_one;
+#endif
+#if __cpp_lib_atomic_flag_test
using std::atomic_flag_test;
using std::atomic_flag_test_and_set;
using std::atomic_flag_test_and_set_explicit;
using std::atomic_flag_test_explicit;
+#endif
+#if __cpp_lib_atomic_wait
using std::atomic_flag_wait;
using std::atomic_flag_wait_explicit;
+#endif
using std::atomic_init;
using std::atomic_int;
using std::atomic_int16_t;
@@ -602,8 +608,10 @@ export namespace std
using std::atomic_load;
using std::atomic_load_explicit;
using std::atomic_long;
+#if __cpp_lib_atomic_wait
using std::atomic_notify_all;
using std::atomic_notify_one;
+#endif
using std::atomic_ptrdiff_t;
using std::atomic_ref;
using std::atomic_schar;
@@ -638,8 +646,10 @@ export namespace std
using std::atomic_unsigned_lock_free;
#endif
using std::atomic_ushort;
+#if __cpp_lib_atomic_wait
using std::atomic_wait;
using std::atomic_wait_explicit;
+#endif
using std::atomic_wchar_t;
using std::kill_dependency;
using std::memory_order;
@@ -997,6 +1007,7 @@ export namespace std
}
// 33.7 <condition_variable>
+#if _GLIBCXX_HAS_GTHREADS
export namespace std
{
using std::condition_variable;
@@ -1004,6 +1015,7 @@ export namespace std
using std::cv_status;
using std::notify_all_at_thread_exit;
}
+#endif
// 17.12.2 <coroutine>
#if __cpp_lib_coroutine
@@ -1762,10 +1774,12 @@ export namespace std
}
// <latch>
+#if __cpp_lib_latch
export namespace std
{
using std::latch;
}
+#endif
// 17.3.3 <limits> [limits.syn]
export namespace std
@@ -2037,7 +2051,9 @@ export namespace std::pmr
using std::pmr::polymorphic_allocator;
using std::pmr::pool_options;
using std::pmr::set_default_resource;
+#if _GLIBCXX_HAS_GTHREADS
using std::pmr::synchronized_pool_resource;
+#endif
using std::pmr::unsynchronized_pool_resource;
}
@@ -2051,13 +2067,19 @@ export namespace std
using std::defer_lock_t;
using std::lock;
using std::lock_guard;
+#if _GLIBCXX_HAS_GTHREADS
using std::mutex;
+#endif
using std::once_flag;
+#if _GLIBCXX_HAS_GTHREADS
using std::recursive_mutex;
using std::recursive_timed_mutex;
+#endif
using std::scoped_lock;
using std::swap;
+#if _GLIBCXX_HAS_GTHREADS
using std::timed_mutex;
+#endif
using std::try_lock;
using std::try_to_lock;
using std::try_to_lock_t;
@@ -2645,11 +2667,13 @@ export namespace std
}
// <semaphore>
+#if __cpp_lib_semaphore
export namespace std
{
using std::binary_semaphore;
using std::counting_semaphore;
}
+#endif
// <set>
export namespace std
@@ -2671,8 +2695,10 @@ export namespace std
export namespace std
{
using std::shared_lock;
+#if _GLIBCXX_HAS_GTHREADS
using std::shared_mutex;
using std::shared_timed_mutex;
+#endif
using std::swap;
}
@@ -2957,7 +2983,9 @@ export namespace std
{
using std::swap;
using std::thread;
+#if __cpp_lib_jthread
using std::jthread;
+#endif
namespace this_thread
{
using std::this_thread::get_id;
--
2.51.1