On Fri, Oct 17, 2025 at 07:33:37PM +0200, Matthieu Baerts (NGI0) wrote:
Two backports linked to build issues with GCC 15 have failed in this version:
- ee2ab467bddf ("x86/boot: Use '-std=gnu11' to fix build with GCC 15")
- 8ba14d9f490a ("efi: libstub: Use '-std=gnu11' to fix build with GCC 15")
Conflicts have been solved, and described.
After that, this kernel version still didn'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; | ^~~~~~~
I initially fixed this by adding -std=gnu11 in arch/x86/Makefile, then I realised this fix was already done in an upstream commit, created before the GCC 15 release and not mentioning the error I had. This is patch 3.
When I was investigating my error, I noticed other commits were already backported to stable versions. They were all adding -std=gnu11 in different Makefiles. In their commit message, they were mentioning 'gnu11' was picked to use the same as the one from the main Makefile. But this is not the case in this kernel version. Patch 4 fixes that.
Finally, I noticed extra warnings I didn't have in v5.10. Patch 5 fixes that.
5.4 is only going to be alive for about 1 more month, so I really don't think trying to "downgrade" things here is worth it at all. Anyone still stuck on this old, obsolete, and very insecure kernel tree isn't going to be attempting to build it using the bleeding edge gcc release :)
So thanks for the patches, but i'll hold off on them for now.
thanks,
greg k-h