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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-486eb359f38sm7798317f8f.30.2026.09.11.14.01.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 11 Sep 2026 14:01:05 -0700 (PDT) Date: Fri, 11 Sep 2026 22:01:02 +0100 From: David Laight To: "Lorenzo Stoakes (ARM)" Cc: Nicolas Schier , Nathan Chancellor , Linus Torvalds , Nick Desaulniers , Bill Wendling , Justin Stitt , Masahiro Yamada , Alexey Gladkov , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Arnd Bergmann , Catalin Marinas , Will Deacon , Mark Rutland , Ard Biesheuvel , Ilias Apalodimas , Josh Poimboeuf , Peter Zijlstra , Miguel Ojeda , Boqun Feng , Gary Guo , =?UTF-8?B?QmrDtnJu?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Daniel Almeida , Tamir Duberstein , Alexandre Courbot , Onur =?UTF-8?B?w5Z6a2Fu?= , Jonathan Corbet , Randy Dunlap , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-efi@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-doc@vger.kernel.org, Jens Axboe Subject: Re: [PATCH 12/23] kbuild: avoid re-running compiler and linker probes Message-ID: <20260911220102.1d3d696a@pumpkin> In-Reply-To: References: <20260908-build-speedup-v1-0-5dc1ac01672d@kernel.org> <20260908-build-speedup-v1-12-5dc1ac01672d@kernel.org> <178901395292.3971858.13236774094648272066.b4-review@b4> <20260910-translucent-sweet-sidewinder-7acacb@l-nschier-aarch64> <20260911183333.1df0f2e2@pumpkin> <20260911-invaluable-indigo-seal-e31aec@l-nschier-aarch64> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Fri, 11 Sep 2026 19:24:50 +0100 "Lorenzo Stoakes (ARM)" wrote: > On Fri, Sep 11, 2026 at 08:17:57PM +0200, Nicolas Schier wrote: > > On Fri, Sep 11, 2026 at 06:33:33PM +0100, David Laight wrote: > > > On Thu, 10 Sep 2026 17:42:35 +0200 > > > Nicolas Schier wrote: > > > > > > ... > > > > Yes, skimming through the patch, I thought about that, too. Moving more > > > > cc option checks to Kconfig will make building out-of-tree kmods with a > > > > different compiler more dangerous. Maybe we will have to make the > > > > warning in Makefile's prepare (external kmods) target a bit louder. > > > > > > One problem is that distributions have a nasty habit of shipping kernels > > > that are compiled with a different compiler version to they actually > > > ship as a compiler. > > > In some cases the versions are clearly the same - but the version > > > strings differ. > > > > yeah, I guess you hit the mark. > > I mean this is a problem that already exists for any flags already specified in > Kconfig. > > Out-of-tree modules are historically something that we don't go to great lengths > to support and haven't historically worried about breaking, either. > > I'm sure distros can find ways around this if a problem were to arise. But I > don't think it's something to worry about all that much. > > I expect a _lot_ of these, in any case, would only require the compilers to be > within a fair few major versions of one another anyway. That is true at the moment when the version of the compiler being used is checked. For instance it doesn't matter if modules are compiled without 'asm goto with output'. But if you putting the options in Kconfig the compiler being used better not be older - or it might not support the options. It isn't too bad if the compile fails, but some are silent. IIRC it is Ubuntu that has different version strings for the same compiler version, and Oracle that ships kernels compiled with much newer compilers that they install by default. David > > > > > -- > > Nicolas > > -- > Cheers, Lorenzo