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

Jason Merrill <[email protected]>
Newsgroups gmane.comp.gcc.patches,gmane.comp.gcc.regression,gmane.comp.gcc.libstdc++.devel,gmane.linux.linaro.toolchain
Message-ID <[email protected]> 
On 12/6/25 11:52 AM, [email protected] 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 <[email protected]>
>    | 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
0001-libstdc-add-more-if-to-std.cc.patch (text/x-patch, 3.9 KB) 
From e098c651d9269e8ddb36dbf43cfe1876f5f40168 Mon Sep 17 00:00:00 2001
From: Jason Merrill <[email protected]>
Date: Sat, 6 Dec 2025 15:55:43 +0800
Subject: [PATCH] libstdc++: add more #if to std.cc
To: [email protected]

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(+)

diff --git a/libstdc++-v3/src/c++23/std.cc.in b/libstdc++-v3/src/c++23/std.cc.in
index c2a9293b05a..4962d4fc598 100644
--- a/libstdc++-v3/src/c++23/std.cc.in
+++ b/libstdc++-v3/src/c++23/std.cc.in
@@ -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
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