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Thu, 12 Mar 2026 15:01:13 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20260105090422.6243-1-ubizjak@gmail.com> <176891088183.510.8607818928752445249.tip-bot2@tip-bot2> <3A54B6DC-2462-41DA-8C34-D38CCD2A9A2B@zytor.com> <38489a10-a081-4dd4-b50c-27c13189acfb@zytor.com> In-Reply-To: From: Uros Bizjak Date: Thu, 12 Mar 2026 23:01:01 +0100 X-Gm-Features: AaiRm51qp89Zz5L5huQrLPRknTGvN4psBFDhQzsVSaSGtWmn8qqqRbDRhMTwBhk Message-ID: Subject: Re: [tip: x86/cleanups] x86/segment: Use MOVL when reading segment registers To: "H. Peter Anvin" Cc: linux-kernel@vger.kernel.org, "Borislav Petkov (AMD)" , x86@kernel.org, Dave Hansen , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , David Laight Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, Mar 12, 2026 at 8:50=E2=80=AFPM Uros Bizjak wro= te: > > On Thu, Mar 12, 2026 at 8:12=E2=80=AFPM H. Peter Anvin wr= ote: > > > > Note: I personally *hate* the savesegment() syntax. For one thing, I wo= uld > > much rather see a more C-like syntax, even if that means making a bunch= of > > inline functions. Replacing the macro with something that is actually > > type-safe would be a bloody good thing, too. > > > > Something like: > > > > /* Generates register operation */ > > static inline unsigned int ds(void) > > { > > unsigned int v; > > asm volatile("mov %%ds,%0" : "=3Dr" (v)); > > return v; > > } > > Yes, this would be much better, but should be unsigned long, because > move from segment register zero-extends all the way to 64-bits: > > static inline unsigned long read_ds(void) > { > unsigned long v; > asm volatile("mov %%ds,%k0" : "=3Dr" (v)); > return v; > } Now implemented at [1]. [1] https://lore.kernel.org/lkml/20260312215916.258176-4-ubizjak@gmail.com/= T/#u Uros.