[Buildroot] [PATCH 1/1] package/glibc: add upstream patch to fix build error with glibc 2.43

[Buildroot] [PATCH 1/1] package/glibc: add upstream patch to fix build error with glibc 2.43

[Bernd Kuhls]

Seen with this defconfig

BR2_x86_64=y
BR2_GCC_VERSION_15_X=y
BR2_TOOLCHAIN_BUILDROOT_CXX=y
BR2_PACKAGE_PICOTOOL=y

output/host/x86_64-buildroot-linux-gnu/sysroot/usr/include/bits/struct_mutex.h:35:9:
 error: declaration does not declare anything [-fpermissive]
   35 |   short __unused;

No related autobuilder error was recorded.
The build error does not occur with glibc-2.42 on the 2026.02.x branch.

The build error was reported to picotool upstream:
https://github.com/raspberrypi/picotool/issues/300

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
---
 ...-__unused-fields-to-__glibc_reserved.patch | 85 +++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 package/glibc/0001-Rename-__unused-fields-to-__glibc_reserved.patch

diff --git a/package/glibc/0001-Rename-__unused-fields-to-__glibc_reserved.patch b/package/glibc/0001-Rename-__unused-fields-to-__glibc_reserved.patch
new file mode 100644
index 0000000000..5b7172df44
--- /dev/null
+++ b/package/glibc/0001-Rename-__unused-fields-to-__glibc_reserved.patch
@@ -0,0 +1,85 @@
+From 243bdfec8f7cd4a85a8ce6e4e9a5a5accd3ce1aa Mon Sep 17 00:00:00 2001
+From: Jakub Jelinek <jakub@redhat.com>
+Date: Tue, 17 Feb 2026 17:06:48 +0100
+Subject: [PATCH] Rename __unused fields to __glibc_reserved.
+
+__unused is often defined to __attribute__((unused)) in BSD
+sources and furthermore libstdc++ testsuite uses it as a macro
+to verify libstdc++ headers don't use __unused identifiers.
+In ~2012 glibc headers have been cleaned up, but some new
+uses of __unused have reappeared (s390 fenv.h already many
+years ago, the rest last November).
+
+Reviewed-by: Florian Weimer <fweimer@redhat.com>
+
+Upstream: https://sourceware.org/git/?p=glibc.git;a=commit;h=243bdfec8f7cd4a85a8ce6e4e9a5a5accd3ce1aa
+
+Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
+---
+ sysdeps/powerpc/nptl/bits/struct_mutex.h | 2 +-
+ sysdeps/s390/fpu/bits/fenv.h             | 8 ++++----
+ sysdeps/s390/nptl/bits/struct_mutex.h    | 2 +-
+ sysdeps/x86/nptl/bits/struct_mutex.h     | 2 +-
+ 4 files changed, 7 insertions(+), 7 deletions(-)
+
+diff --git a/sysdeps/powerpc/nptl/bits/struct_mutex.h b/sysdeps/powerpc/nptl/bits/struct_mutex.h
+index 1472af21f7..ebf2d50922 100644
+--- a/sysdeps/powerpc/nptl/bits/struct_mutex.h
++++ b/sysdeps/powerpc/nptl/bits/struct_mutex.h
+@@ -32,7 +32,7 @@ struct __pthread_mutex_s
+   int __kind;
+ #if __WORDSIZE == 64
+   short __spins;
+-  short __unused;
++  short __glibc_reserved;
+   __pthread_list_t __list;
+ # define __PTHREAD_MUTEX_HAVE_PREV      1
+ #else
+diff --git a/sysdeps/s390/fpu/bits/fenv.h b/sysdeps/s390/fpu/bits/fenv.h
+index b9e844e393..33e88fbe9d 100644
+--- a/sysdeps/s390/fpu/bits/fenv.h
++++ b/sysdeps/s390/fpu/bits/fenv.h
+@@ -76,10 +76,10 @@ typedef unsigned int fexcept_t; /* size of fpc */
+ typedef struct
+ {
+   fexcept_t __fpc;
+-  void *__unused;
+-  /* The field __unused (formerly __ieee_instruction_pointer) is a relict from
+-     commit "Remove PTRACE_PEEKUSER" (87b9b50f0d4b92248905e95a06a13c513dc45e59)
+-     and isn't used anymore.  */
++  void *__glibc_reserved;
++  /* The field __glibc_reserved (formerly __ieee_instruction_pointer) is a
++     relict from commit "Remove PTRACE_PEEKUSER"
++     (87b9b50f0d4b92248905e95a06a13c513dc45e59) and isn't used anymore.  */
+ } fenv_t;
+ 
+ /* If the default argument is used we use this value.  */
+diff --git a/sysdeps/s390/nptl/bits/struct_mutex.h b/sysdeps/s390/nptl/bits/struct_mutex.h
+index d069b485d1..571265267c 100644
+--- a/sysdeps/s390/nptl/bits/struct_mutex.h
++++ b/sysdeps/s390/nptl/bits/struct_mutex.h
+@@ -32,7 +32,7 @@ struct __pthread_mutex_s
+   int __kind;
+ #if __WORDSIZE == 64
+   short __spins;
+-  short __unused;
++  short __glibc_reserved;
+   __pthread_list_t __list;
+ # define __PTHREAD_MUTEX_HAVE_PREV      1
+ #else
+diff --git a/sysdeps/x86/nptl/bits/struct_mutex.h b/sysdeps/x86/nptl/bits/struct_mutex.h
+index 9c19dff660..13c9894ad4 100644
+--- a/sysdeps/x86/nptl/bits/struct_mutex.h
++++ b/sysdeps/x86/nptl/bits/struct_mutex.h
+@@ -32,7 +32,7 @@ struct __pthread_mutex_s
+   int __kind;
+ #ifdef __x86_64__
+   short __spins;
+-  short __unused;
++  short __glibc_reserved;
+   __pthread_list_t __list;
+ # define __PTHREAD_MUTEX_HAVE_PREV      1
+ #else
+-- 
+2.47.3
+
-- 
2.47.3

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Re: [Buildroot] [PATCH 1/1] package/glibc: add upstream patch to fix build error with glibc 2.43

[Thomas Petazzoni via buildroot]

On Fri, May 01, 2026 at 07:14:32PM +0200, Bernd Kuhls wrote:
> Seen with this defconfig
> 
> BR2_x86_64=y
> BR2_GCC_VERSION_15_X=y
> BR2_TOOLCHAIN_BUILDROOT_CXX=y
> BR2_PACKAGE_PICOTOOL=y
> 
> output/host/x86_64-buildroot-linux-gnu/sysroot/usr/include/bits/struct_mutex.h:35:9:
>  error: declaration does not declare anything [-fpermissive]
>    35 |   short __unused;
> 
> No related autobuilder error was recorded.
> The build error does not occur with glibc-2.42 on the 2026.02.x branch.
> 
> The build error was reported to picotool upstream:
> https://github.com/raspberrypi/picotool/issues/300
> 
> Signed-off-by: Bernd Kuhls <bernd@kuhls.net>

Thanks, applied to master. Do you happen to know why glibc upstream
didn't include this patch in its 2.43 maintenance branch, if it fixes
a bug? Maybe something to report to them?

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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