Hi Kostadin, Just a quick FYI off the bat, you only directed this to LKML, which is basically like sending it into the void because very few people actually read every message on LKML. I only caught it because I have a filter set up for mentions of Clang and LLVM. I'd suggest adding at least the Kbuild mailing list, which I have done now. I have also added Arnd because I seem to recall him looking into how hard it would be to build the kernel with C23. On Mon, Nov 18, 2024 at 02:26:49PM +0000, Kostadin Shishmanov wrote: > Whenever I try to build the kernel with upcoming GCC 15 which defaults to -std=gnu23 I get a build failure: > > ``` > 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 ./include/uapi/linux/mei_uuid.h:12, > from ./include/uapi/linux/mei.h:10, > from ./include/linux/mod_devicetable.h:12, > from scripts/mod/devicetable-offsets.c:3: > ./include/linux/stddef.h:11:9: error: expected identifier before ‘false’ > 11 | false = 0, > ./include/linux/types.h:35:33: error: two or more data types in declaration specifiers > 35 | typedef _Bool bool; > ./include/linux/types.h:35:1: warning: useless type name in empty declaration > 35 | typedef _Bool bool; > ``` > > This can be reproduced on older GCC versions with KCFLAGS="-std=gnu23" The kernel builds explicitly with '-std=gnu11' (see Makefile), so I would not expect the default switch on the GCC side to matter. That signals to me that we are not actually using that flag everywhere then? Building with V=1, I can see '-std=gnu11' in the compiler command for scripts/mod/devicetable-offsets.s, which is generated from scripts/mod/devicetable-offsets.c, so it seems like something else is going on here? > With Clang 18 and KCFLAGS="-std=c23" it's an even bigger mess: I think the error below occurs because you used 'c23' instead of 'gnu23'. GCC's documentation states: "The asm keyword is a GNU extension. When writing code that can be compiled with -ansi and the various -std options, use __asm__ instead of asm (see Alternate Keywords)." https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html Cheers, Nathan > ``` > In file included from ./arch/x86/include/asm/jump_label.h:7, > from ./include/linux/jump_label.h:112, > from ./arch/x86/include/asm/string_64.h:6, > from ./arch/x86/include/asm/string.h:5, > from ./include/linux/string.h:64, > from ./include/linux/uuid.h:11, > from ./include/linux/mod_devicetable.h:14: > ./arch/x86/include/asm/asm.h: In function ‘rip_rel_ptr’: > ./arch/x86/include/asm/asm.h:120:9: error: implicit declaration of function ‘asm’ [-Wimplicit-function-declaration] > 120 | asm("leaq %c1(%%rip), %0" : "=r"(p) : "i"(p)); > ./arch/x86/include/asm/asm.h:120:34: error: expected ‘)’ before ‘:’ token > 120 | asm("leaq %c1(%%rip), %0" : "=r"(p) : "i"(p)); > ./arch/x86/include/asm/asm.h: At top level: > ./arch/x86/include/asm/asm.h:222:46: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘asm’ > 222 | register unsigned long current_stack_pointer asm(_ASM_SP); > ./arch/x86/include/asm/jump_label.h: In function ‘arch_static_branch’: > ./arch/x86/include/asm/jump_label.h:27:9: error: ‘asm’ undeclared (first use in this function) > 27 | asm goto("1:" > ./arch/x86/include/asm/jump_label.h:27:9: note: each undeclared identifier is reported only once for each function it appears in > ./arch/x86/include/asm/jump_label.h:27:12: error: expected ‘;’ before ‘goto’ > 27 | asm goto("1:" > ; > In file included from ./include/uapi/linux/swab.h:8, > from ./include/linux/swab.h:5, > from ./include/uapi/linux/byteorder/little_endian.h:14, > from ./include/linux/byteorder/little_endian.h:5, > from ./arch/x86/include/uapi/asm/byteorder.h:5, > from ./include/linux/bitfield.h:11, > from ./include/linux/fortify-string.h:5, > from ./include/linux/string.h:390: > ./arch/x86/include/uapi/asm/swab.h: In function ‘__arch_swab32’: > ./arch/x86/include/uapi/asm/swab.h:10:24: error: expected ‘)’ before ‘:’ token > 10 | asm("bswapl %0" : "=r" (val) : "0" (val)); > ) > ./arch/x86/include/uapi/asm/swab.h: In function ‘__arch_swab64’: > ./arch/x86/include/uapi/asm/swab.h:31:24: error: expected ‘)’ before ‘:’ token > 31 | asm("bswapq %0" : "=r" (val) : "0" (val)); > ) > In file included from scripts/mod/devicetable-offsets.c:2: > scripts/mod/devicetable-offsets.c: In function ‘main’: > ./include/linux/kbuild.h:6:9: error: ‘asm’ undeclared (first use in this function) > 6 | asm volatile("\n.ascii \"->" #sym " %0 " #val "\"" : : "i" (val)) > scripts/mod/devicetable-offsets.c:5:22: note: in expansion of macro ‘DEFINE’ > 5 | #define DEVID(devid) DEFINE(SIZE_##devid, sizeof(struct devid)) > scripts/mod/devicetable-offsets.c:11:9: note: in expansion of macro ‘DEVID’ > 11 | DEVID(usb_device_id); > ./include/linux/kbuild.h:6:13: error: expected ‘;’ before ‘volatile’ > 6 | asm volatile("\n.ascii \"->" #sym " %0 " #val "\"" : : "i" (val)) > ``` > > There is a lot more output from the compiler that i've cut off because the email would become way too long. > > Regards, > Kostadin >
