On Tue, May 9, 2023, at 09:05, Tiezhu Yang wrote: > Now we specify the minimal version of GCC as 5.1 and Clang/LLVM as 11.0.0 > in Documentation/process/changes.rst, __CHAR_BIT__ and __SIZEOF_LONG__ are > usable, just define __BITS_PER_LONG as (__CHAR_BIT__ * __SIZEOF_LONG__) in > asm-generic uapi bitsperlong.h, simpler, works everywhere. > > Remove all the arch specific uapi bitsperlong.h which will be generated as > arch/*/include/generated/uapi/asm/bitsperlong.h. > > Suggested-by: Xi Ruoyao <xry111@xxxxxxxxxxx> > Link: > https://lore.kernel.org/all/d3e255e4746de44c9903c4433616d44ffcf18d1b.camel@xxxxxxxxxxx/ > Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> I originally introduced the bitsperlong.h header, and I'd love to see it removed if it's no longer needed. Your patch certainly seems like it does this well. There is one minor obstacle to this, which is that the compiler requirements for uapi headers are not the same as for kernel internal code. In particular, the uapi headers may be included by user space code that is built with an older compiler version, or with a compiler that is not gcc or clang. I think we are completely safe on the architectures that were added since the linux-3.x days (arm64, riscv, csky, openrisc, loongarch, nios2, and hexagon), but for the older ones there is a regression risk. Especially on targets that are not that actively maintained (sparc, alpha, ia64, sh, ...) there is a good chance that users are stuck on ancient toolchains. It's probably also a safe assumption that anyone with an older libc version won't be using the latest kernel headers, so I think we can still do this across architectures if both glibc and musl already require a compiler that is new enough, or alternatively if we know that the kernel headers require a new compiler for other reasons and nobody has complained. For glibc, it looks the minimum compiler version was raised from gcc-5 to gcc-8 four years ago, so we should be fine. In musl, the documentation states that at least gcc-3.4 or clang-3.2 are required, which probably predate the __SIZEOF_LONG__ macro. On the other hand, musl was only released in 2011, and building musl itself explicitly does not require kernel uapi headers, so this may not be too critical. There is also uClibc, but I could not find any minimum supported compiler version for that. Most commonly, this one is used for cross-build environments, so it's also less likely to have libc/gcc/headers being wildly out of sync. Not sure. Arnd [1] https://sourceware.org/pipermail/libc-alpha/2019-January/101010.html
