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Peter Anvin" , Linus Torvalds Subject: Re: [PATCH v1] x86/mm/pat: (un)track_pfn_copy() fix + improvements Message-ID: <20250408025129.GA1168636@ax162> References: <20250404124931.2255618-1-david@redhat.com> <630caa8e-2ee2-4895-9e4e-8bf2fa079100@redhat.com> <4961949a-75db-4071-a478-fdc543c1dd28@stanley.mountain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 1EA67180005 X-Stat-Signature: 8eynewcp75kknyw7ujpfkobgqt3wnah5 X-Rspam-User: X-HE-Tag: 1744080696-46248 X-HE-Meta: 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 eeKdOVmk GrhZQ+yrzdfDFuoM0wLA2oVL4bKFoi62suQcgIY2nTxjhx/NKigIkqzhh4hHBMKDzdo1uWT20DkfNi1VxzAWSxYn/Rx/w8kLvdOxGZGVSOUH+SwhCL9LQWaB9qvJCREXkG6xmbO6oqRCPsU4cSD/wZk+HfP7nXzl8dE6pe20PwZFHem9HXdKsgfyUNx+H6LeoJiJVOjS0e4gHqwc7fmC2kYHhx1eyDMF2vEgRwd0LfuMlbA3AMt3BYU0OOyAhAXi5CDmZlD00tEOIj/d5kXRgQvM/CRu6QusgUzGe+iJNMJyf33MMeXojMZaXYn5cBrBwC6kivEt1vPPm/GcuxoDL3/sjqDssvFEo9J1RTZvsbJ2fw6xQhU61Z6RGkQ== 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: 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 Cheers, Nathan