From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tiezhu Yang Subject: Re: [RFC PATCH] asm-generic: Unify uapi bitsperlong.h Date: Thu, 8 Jun 2023 15:04:13 +0800 Message-ID: <76d3be65-91df-7969-5303-38231a7df926@loongson.cn> References: <1683615903-10862-1-git-send-email-yangtiezhu@loongson.cn> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From:Cc: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=trPIJTOFtizg5ESqcWgeUWh5Hs4lceXzuWshzrB+4Lw=; b=DlMZYPO3s3QI1pZ492ZsUGbtf8 e2IydAbwfqNf+ShsxUnk3yHoeVh1sfp2WsGjyzGl9nYmX2xI8Bjtzmy4IiP8l3te5+GpWpELeAgQ0 gPxT9deGTGwDodeC47ZFXzie7yKRnNM2KZUAOFgEAJAzeuLhtEdvHgDXtw7h8VxGehdcxrB3JXYeD znE+e/z+qIvP8t49LDFv4aSmGtpwMwa+FVNWq1pG4wyV8ZprMdJCzhwDn6WqVW74kup3tfUSo/e4Q 1qo4ie+h9z2kYZQl2pKptoInRwplBM56yumbzJth7/uOH6dP/y550+L6ShOE1gZ0qvumChKnqJzHH 6oAWUCLg==; In-Reply-To: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-riscv" Errors-To: linux-riscv-bounces+glpr-linux-riscv=m.gmane-mx.org@lists.infradead.org Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Arnd Bergmann Cc: linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, x86@kernel.org, bpf@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-kselftest@vger.kernel.org, Linux-Arch , llvm@lists.linux.dev, linux-kernel@vger.kernel.org, loongson-kernel@lists.loongnix.cn Hi all, On 05/09/2023 05:37 PM, Arnd Bergmann wrote: > 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 >> Link: >> https://lore.kernel.org/all/d3e255e4746de44c9903c4433616d44ffcf18d1b.camel@xry111.site/ >> Signed-off-by: Tiezhu Yang > > 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 > Thanks Arnd for the detailed reply. Any more comments? What should I do in the next step? Thanks, Tiezhu