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Peter Anvin" , Linus Torvalds Subject: Re: [PATCH v1] x86/mm/pat: (un)track_pfn_copy() fix + improvements Message-ID: References: <20250404124931.2255618-1-david@redhat.com> <630caa8e-2ee2-4895-9e4e-8bf2fa079100@redhat.com> <4961949a-75db-4071-a478-fdc543c1dd28@stanley.mountain> <20250408025129.GA1168636@ax162> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250408025129.GA1168636@ax162> X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: EAA244000A X-Stat-Signature: jt58cfzmxuxsno1qoi8ri85npk8syhuz X-Rspam-User: X-HE-Tag: 1744100374-891941 X-HE-Meta: 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 9ViOgTb8 80HIvNCsPA7YJ4RKeJiOu1rGAS7qJDFI+hKIlf1f9e3VZzJB4ncJDs3bCLYmGJGlbymE1FSbXlM025yhwWJotTUJ5qPJFbkUcxSvKPFaiyUDhBDcNHCA8i00FcRV4DZPMZyZQkDpUm5LObP/xsqFB45wbqhKp202GJe0sloEjtvkUMgbldANZBFt+xSuq2t0VKd35v3xgvKwqqFtMx2T4kIRhBfQg6QJ2wMBt72suMxGHqp1BB7SXPaWlSQaQ8ENLO+pQd4IIF14Fp/jqZMLZgNarYH3M4o8Zxqqu79+PHFOtkvsX2IlLa/WarHycm9IPdZ/N883e1knUhQg= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: * Nathan Chancellor wrote: > On Mon, Apr 07, 2025 at 08:59:44PM +0200, Ingo Molnar wrote: > > Good, although why is this compiler option named so weirdly in Clang: > > > > CC_AUTO_VAR_INIT_ZERO_ENABLER := -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang > > > > Hopefully it is named thusly because Clang has adopted GCC's > > -ftrivial-auto-var-init=zero? > > Clang did -ftrivial-auto-var-init first, where the original author added > both pattern and zero but intended to remove zero once pattern has been > optimized enough compared to zero (if I remember and understand > correctly), so the "enabler" flag was added to try and make that clear. > Eventually, Kees leveraged both Linus's stated desire for initializing > stack variables [1] and GCC 12 landing -ftrivial-auto-var-init=zero > without a separate enable option to deprecate the "enabler" flag in > clang 16 [2] and remove it altogether in clang 18 [3]. > > [1]: https://lore.kernel.org/CAHk-=wgTM+cN7zyUZacGQDv3DuuoA4LORNPWgb1Y_Z1p4iedNQ@mail.gmail.com/ > [2]: https://github.com/llvm/llvm-project/commit/aef03c9b3bed5cef5a1940774b80128aefcb4095 > [3]: https://github.com/llvm/llvm-project/commit/00e54d04ae2802d498741097d4b83e898bc99c5b Cool, thanks for the explanation! Thanks, Ingo