Hi all,

GCC 15 changed the default C standard dialect from gnu17 to gnu23, which should not have impacted the kernel because it explicitly requests the gnu11 standard in the main Makefile. However I see these errors in older kernels series and some realtime kernels:

5.4, 5.10, 5.15, 6.1, 6.1-rt, 6.6, 6.13-rt

2025-04-30T19:26:10.5226566Z from arch/x86/realmode/rm/wakemain.c:2: 2025-04-30T19:26:10.5228293Z ./include/linux/stddef.h:11:9: error: cannot use keyword ‘false’ as enumeration constant 2025-04-30T19:26:10.5229525Z 11 | false = 0, 2025-04-30T19:26:10.5230691Z | ^~~~~ 2025-04-30T19:26:10.5232337Z ./include/linux/stddef.h:11:9: note: ‘false’ is a keyword with ‘-std=c23’ onwards 2025-04-30T19:26:10.5234141Z ./include/linux/types.h:30:33: error: ‘bool’ cannot be defined via ‘typedef’ 2025-04-30T19:26:10.5235478Z 30 | typedef _Bool bool; 2025-04-30T19:26:10.5236557Z | ^~~~ 2025-04-30T19:26:10.5238016Z ./include/linux/types.h:30:33: note: ‘bool’ is a keyword with ‘-std=c23’ onwards 2025-04-30T19:26:10.5239544Z ./include/linux/types.h:30:1: warning: useless type name in empty declaration 2025-04-30T19:26:10.5241119Z 30 | typedef _Bool bool; 2025-04-30T19:26:10.5242189Z | ^~~~~~~ 2025-04-30T19:26:10.5351835Z make[4]: *** [scripts/Makefile.build:250: arch/x86/realmode/rm/wakemain.o] Error 1 2025-04-30T19:26:10.5362380Z make[3]: *** [arch/x86/realmode/Makefile:22: arch/x86/realmode/rm/realmode.bin] Error 2

I found this with mips: https://lkml.iu.edu/hypermail/linux/kernel/2503.2/09285.html

Do we miss some patch not backported?