This is a note to let you know that I've just added the patch titled

    x86/boot: Compile boot code with -std=gnu11 too

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-boot-compile-boot-code-with-std-gnu11-too.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From matttbe@kernel.org Sat Oct 18 01:24:24 2025
From: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>
Date: Fri, 17 Oct 2025 18:24:00 +0200
Subject: x86/boot: Compile boot code with -std=gnu11 too
To: stable@vger.kernel.org, Greg Kroah-Hartman <gregkh@linuxfoundation.org>,  Sasha Levin <sashal@kernel.org>
Cc: MPTCP Upstream <mptcp@lists.linux.dev>,  "Matthieu Baerts (NGI0)" <matttbe@kernel.org>,  Alexey Dobriyan <adobriyan@gmail.com>, Ingo Molnar <mingo@kernel.org>,  "H. Peter Anvin (Intel)" <hpa@zytor.com>,  Nathan Chancellor <nathan@kernel.org>,  Dave Hansen <dave.hansen@linux.intel.com>, Ard Biesheuvel <ardb@kernel.org>
Message-ID: <20251017-v5-15-gcc-15-v1-1-da6c065049d7@kernel.org>

From: Alexey Dobriyan <adobriyan@gmail.com>

commit b3bee1e7c3f2b1b77182302c7b2131c804175870 upstream.

Use -std=gnu11 for consistency with main kernel code.

It doesn't seem to change anything in vmlinux.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Link: https://lore.kernel.org/r/2058761e-12a4-4b2f-9690-3c3c1c9902a5@p183
[ This kernel version doesn't build with GCC 15:
    In file included from include/uapi/linux/posix_types.h:5,
                     from include/uapi/linux/types.h:14,
                     from include/linux/types.h:6,
                     from arch/x86/realmode/rm/wakeup.h:11,
                     from arch/x86/realmode/rm/wakemain.c:2:
    include/linux/stddef.h:11:9: error: cannot use keyword 'false' as enumeration constant
       11 |         false   = 0,
          |         ^~~~~
    include/linux/stddef.h:11:9: note: 'false' is a keyword with '-std=c23' onwards
    include/linux/types.h:30:33: error: 'bool' cannot be defined via 'typedef'
       30 | typedef _Bool                   bool;
          |                                 ^~~~
    include/linux/types.h:30:33: note: 'bool' is a keyword with '-std=c23' onwards
    include/linux/types.h:30:1: warning: useless type name in empty declaration
       30 | typedef _Bool                   bool;
          | ^~~~~~~

  The fix is similar to commit ee2ab467bddf ("x86/boot: Use '-std=gnu11'
  to fix build with GCC 15") which has been backported to this kernel.

  Note: In < 5.18 version, -std=gnu89 is used instead of -std=gnu11, see
  commit e8c07082a810 ("Kbuild: move to -std=gnu11"). I suggest not to
  modify that in this commit here as all the other similar fixes to
  support GCC 15 set -std=gnu11. This can be done in a dedicated commit
  if needed. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/Makefile |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -24,7 +24,7 @@ endif
 
 # How to compile the 16-bit code.  Note we always compile for -march=i386;
 # that way we can complain to the user if the CPU is insufficient.
-REALMODE_CFLAGS	:= -m16 -g -Os -DDISABLE_BRANCH_PROFILING -D__DISABLE_EXPORTS \
+REALMODE_CFLAGS	:= -std=gnu11 -m16 -g -Os -DDISABLE_BRANCH_PROFILING -D__DISABLE_EXPORTS \
 		   -Wall -Wstrict-prototypes -march=i386 -mregparm=3 \
 		   -fno-strict-aliasing -fomit-frame-pointer -fno-pic \
 		   -mno-mmx -mno-sse $(call cc-option,-fcf-protection=none)


Patches currently in stable-queue which might be from matttbe@kernel.org are

queue-5.15/arch-back-to-std-gnu89-in-v5.18.patch
queue-5.15/x86-boot-compile-boot-code-with-std-gnu11-too.patch
queue-5.15/mptcp-drop-bogus-optimization-in-__mptcp_check_push.patch
queue-5.15/mptcp-restore-window-probe.patch
queue-5.15/revert-docs-process-howto-replace-c89-with-c11.patch