Build Errors on GCC 15 and glibc 2.43

[avlec]

With gcc 15.2.1+r604 and glibc 2.43 on Arch Linux this project does not build.

[ 33%] Building CXX object model/CMakeFiles/model.dir/model.cpp.o
In file included from /home/avlec/pico/pico-sdk/src/common/boot_picoboot_headers/include/boot/picoboot.h:15,
                 from /home/avlec/pico/picotool/model/model.h:8,
                 from /home/avlec/pico/picotool/model/model.cpp:1:
/usr/include/bits/struct_mutex.h:35:9: error: declaration does not declare anything [-fpermissive]
   35 |   short __unused;
      |         ^~~~~~~~
In file included from /usr/include/c++/15.2.1/x86_64-pc-linux-gnu/bits/gthr-default.h:35,
                 from /usr/include/c++/15.2.1/x86_64-pc-linux-gnu/bits/gthr.h:157,
                 from /usr/include/c++/15.2.1/ext/atomicity.h:37,
                 from /usr/include/c++/15.2.1/bits/shared_ptr_base.h:61,
                 from /usr/include/c++/15.2.1/bits/shared_ptr.h:53,
                 from /usr/include/c++/15.2.1/memory:82,
                 from /home/avlec/pico/picotool/model/model.h:43:
/usr/include/c++/15.2.1/ext/concurrence.h:124:34: error: cannot convert ‘<brace-enclosed initializer list>’ to ‘__pthread_internal_list*’ in initialization
  124 |     __gthread_mutex_t _M_mutex = __GTHREAD_MUTEX_INIT;
      |                                  ^~~~~~~~~~~~~~~~~~~~
/usr/include/c++/15.2.1/ext/concurrence.h:179:44: error: cannot convert ‘<brace-enclosed initializer list>’ to ‘__pthread_internal_list*’ in initialization
  179 |     __gthread_recursive_mutex_t _M_mutex = __GTHREAD_RECURSIVE_MUTEX_INIT;
      |                                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
make[2]: *** [model/CMakeFiles/model.dir/build.make:79: model/CMakeFiles/model.dir/model.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:802: model/CMakeFiles/model.dir/all] Error 2
make: *** [Makefile:136: all] Error 2

/usr/include/bits/struct_mutex.h

This seems to be a bad glibc header that was fixed recently upstream and is unreleased
https://sourceware.org/git/?p=glibc.git;a=commit;h=243bdfec8f7cd4a85a8ce6e4e9a5a5accd3ce1aa

I do not know how to work around this one... (I just edited the system header with sudo to change __unused to the same thing in the linked glibc commit)

/usr/include/c++/15.2.1/ext/concurrence.h

Similar __GTHREAD failures have cropped up in pico-sdk here raspberrypi/pico-sdk#2746. Linked in that issue is an abandoned fix of which I applied here and it resolves these issues.

diff --git a/model/CMakeLists.txt b/model/CMakeLists.txt
index cd9e775..4879f63 100644
--- a/model/CMakeLists.txt
+++ b/model/CMakeLists.txt
@@ -4,6 +4,10 @@ add_library(model STATIC
 target_include_directories(model PUBLIC ${CMAKE_CURRENT_LIST_DIR} ${CMAKE_CURRENT_BINARY_DIR})

 target_link_libraries(model PUBLIC boot_uf2_headers boot_picoboot_headers pico_platform_headers errors)
+target_compile_definitions(model PRIVATE
+       _GTHREAD_USE_MUTEX_INIT_FUNC
+       _GTHREAD_USE_RECURSIVE_MUTEX_INIT_FUNC
+)

 add_custom_target(unreadable_rom_data DEPENDS
         ${CMAKE_CURRENT_BINARY_DIR}/rp2350_a2_rom_end.h

[tkatter]

Had this same problem with /usr/include/bits/struct_mutex.h on Arch, editing the file with sudo and changing __unused -> __glibc_reserved worked like you mentioned. Thanks for finding that.

[mikee47]

This issue is present in gcc 16.1.1 20260515 (glibc 2.43-5). Other than hacking /usr/include/bits/struct_mutex.h, this patch fixes the problem for picotool. Note that the suggested changes to CMakeLists.txt do not work for me.

diff --git a/model/model.h b/model/model.h
index 17bf824..318b0d2 100644
--- a/model/model.h
+++ b/model/model.h
@@ -4,9 +4,16 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 #pragma once
+
+/* 2026-05-20 Temporary fix for https://github.com/raspberrypi/picotool/issues/300 */
+#undef __unused
+#define __unused __glibc_unused
+
 #include "boot/uf2.h"
 #include "boot/picoboot.h"
 
+#undef __unused
+
 // Unreadable ROM data
 #include "rp2350_a2_rom_end.h"
 #include "rp2350_a3_rom_end.h"
@@ -418,4 +425,7 @@ static bool contains_unreadable_rom(uint32_t addr, uint32_t size, const model_t&
             (addr < model->unreadable_rom_start() && addr + size > model->unreadable_rom_end());
 }
 
-#endif
\ No newline at end of file
+#endif
+
+/* 2026-05-20 Temporary fix for https://github.com/raspberrypi/picotool/issues/300 */
+#define __unused __attribute__((__unused__))

[non-bin]

Seems to be working for me now on debian latest

[shtirlic]

That what helpde me to make it compile on Arch wit all latest:

~/.local/include/ext/concurrence.h

#pragma once
// Shadow header: fix GCC 16 + glibc 2.43 incompatibility
// Redefine broken mutex initializers to use value-init instead of
// PTHREAD_MUTEX_INITIALIZER which contains { NULL, NULL } brace-init
// that GCC 16 rejects for pointer fields.
#include <x86_64-pc-linux-gnu/bits/gthr-default.h>
#undef __GTHREAD_MUTEX_INIT
#undef __GTHREAD_RECURSIVE_MUTEX_INIT
#define __GTHREAD_MUTEX_INIT {}
#define __GTHREAD_RECURSIVE_MUTEX_INIT {}
#include_next <ext/concurrence.h>

and I do cmake like this

cmake -DCMAKE_INSTALL_PREFIX=~/.local \
      -DCMAKE_CXX_FLAGS="-I$HOME/.local/include -fpermissive" \
      ..

[kilograham]

can ppl please confirm which versions of GCC 15 & 16 are broken/working, and whether defining _GTHREAD_USE_COND_INIT_FUNC is a sufficient fix

(note this appears to be a GCC bug, which is why it is fixed in later versions)

[HattonLe]

Ubuntu 26.04, kernel 7.0.0, gcc (Ubuntu 15.2.0-16ubuntu1) 15.2.0, ldd (Ubuntu GLIBC 2.43-2ubuntu2) 2.43.

Never used Pico hardware before so 1st time trying to get pico sdk and things installed on my Ubuntu system.
In the process of doing that its trying to build "picotool" and I'm getting the same error as OP, plus some extra errors out of CMakeFiles/picotool.dir/main.cpp

I've just included the last 20 lines or so of the "main.cpp" errors (as it messes up the comment) as follows...

_In member function ‘_Tp* std::__new_allocator<_Tp>::allocate(size_type, const void*) [with _Tp = unsigned char]’,
inlined from ‘static _Tp* std::allocator_traits<std::allocator<_Tp1> >::allocate(allocator_type&, size_type) [with _Tp = unsigned char]’ at /usr/include/c++/15/bits/alloc_traits.h:614:28,
inlined from ‘std::_Vector_base<_Tp, _Alloc>::pointer std::_Vector_base<_Tp, _Alloc>::_M_allocate(std::size_t) [with _Tp = unsigned char; _Alloc = std::allocator]’ at /usr/include/c++/15/bits/stl_vector.h:387:33,
inlined from ‘void std::_Vector_base<_Tp, _Alloc>::_M_create_storage(std::size_t) [with _Tp = unsigned char; _Alloc = std::allocator]’ at /usr/include/c++/15/bits/stl_vector.h:405:44,
inlined from ‘std::_Vector_base<_Tp, _Alloc>::_Vector_base(std::size_t, const allocator_type&) [with _Tp = unsigned char; _Alloc = std::allocator]’ at /usr/include/c++/15/bits/stl_vector.h:341:26,
inlined from ‘std::vector<_Tp, _Alloc>::vector(size_type, const allocator_type&) [with _Tp = unsigned char; _Alloc = std::allocator]’ at /usr/include/c++/15/bits/stl_vector.h:587:47,
inlined from ‘std::vector memory_access::read_vector(uint32_t, unsigned int, bool) [with T = unsigned char]’ at /home/main/Downloads/pico/picotool/main.cpp:1873:59,
inlined from ‘virtual bool link_command::execute(device_map&)’ at /home/main/Downloads/pico/picotool/main.cpp:5828:85:
/usr/include/c++/15/bits/new_allocator.h:151:73: note: returned from ‘void* operator new(std::size_t)’
151 | return static_cast<_Tp*>(_GLIBCXX_OPERATOR_NEW(_n * sizeof(Tp)));
| ^
ninja: build stopped: subcommand failed.

these "main.cpp" errors all seem to involve macros _GLIBCXX_SIZED_DEALLOC and _GLIBCXX_OPERATOR_NEW.