On Tue, Jun 4, 2019 at 10:44 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Tue, Jun 04, 2019 at 09:48:12PM +0900, Masahiro Yamada wrote: > > 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. > > Just because we have relied on it in the past, does not mean we need to > keep relying on it. I have had numerous complaints over the years from > libc authors that our uapi headers are _NOT_ able to be directly > consumed by them. They all end up having to fix things up and include > local "sanitized" copies. > > So any work we can do here to make them more sane and work properly > everywhere is a good thing, as right now, they are broken. Maybe, we should document UAPI header coding guideline. Without To-Don't list, people will do anything. -- Best Regards Masahiro Yamada
