On Tue, Jun 4, 2019 at 8:55 PM Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Tue, Jun 4, 2019 at 1:23 PM Joe Perches <joe@xxxxxxxxxxx> wrote: > > > > On Tue, 2019-06-04 at 20:13 +0900, Masahiro Yamada wrote: > > > On the other hand, uapi headers are written in more strict C, where > > > the C++ comment style is forbidden. > > > > Is this a real problem for any toolchain? > > There is likely some code that is built with -Wpedandic -Werror --std=c89 > or similar. Since glibc allows this combination for its own headers, it seems > best to also allow it in kernel headers that may be included by libc headers > or by applications, at least where it does not hurt. > > Realistically though, we probably assume c99 or gnu89 in user space > headers anyway, since there is no 'long long' in earlier standards. > > Arnd In fact, I detected this issue by the following patch: https://patchwork.kernel.org/patch/10974669/ When I worked on it, I wondered which c-dialect flags should be used. This code: > # Unlike the kernel space, uapi headers are written in more strict C. > # - Forbid C++ style comments > # - Use '__inline', '__asm__' instead of 'inline', 'asm' > # > # -std=c90 (equivalent to -ansi) catches the violation of those. > # We cannot go as far as adding -Wpedantic since it emits too many warnings. > # > # REVISIT: re-consider the proper set of compiler flags for uapi compile-test. > > UAPI_CFLAGS := -std=c90 -Wpedantic -Wall -Werror=implicit-function-declaration Even "-std=c99 -Wpedantic" emits lots of warnings. I noticed one more thing. There are two ways to define fixed-width type. [1] #include <linux/types.h>, __u8, __u16, __u32, __u64 vs [2] #include <stdint.h>, uint8_t, uint16_t, uint32_t, uint64_t Both are used in UAPI headers. IIRC, <stdint.h> was standardized by C99. So, we have already relied on C99 in user-space too. -- Best Regards Masahiro Yamada
