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Peter Anvin" , Borislav Petkov , Dave Hansen , Ingo Molnar , Jonathan Corbet , Thomas Gleixner Subject: Re: [PATCH] x86: Start removing X86_X32_ABI Date: Wed, 27 May 2026 09:41:39 -0400 Message-ID: In-Reply-To: <20260523093734.A3AR7reJ@linutronix.de> References: <20260523093734.A3AR7reJ@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" On Saturday, May 23, 2026 5:37:34=E2=80=AFAM Eastern Daylight Time Sebastia= n Andrzej=20 Siewior wrote: > The x32 ABI was introduced in v3.4 to leverage the additional registers > which were available on x86_64 but not on i386 while keeping the smaller > 32bit pointers. >=20 > This did not take off. The memory usage usually knows no limit and the > better performance did not reach a point where certain workloads widely > move to x32 and use it exclusively. In the meantime Debian introduced a > patch to disable x32 by default (so it has to be enabled at boot time on > the command line) because they are afraid of the increased attack > surface. Fedora as far as I tell has X32 disabled (looking at 7.0-rc5 > rpm in rawhide). >=20 > The last syscall for x86_64 is currently at 471. The first x32 starts at > 512 which leaves 40 new syscalls in between. Without the x32 ABI, those > syscalls could be used since x32 wouldn't be an option and therefore > reserved. >=20 > Since there is practically no real use for x32, start removing it by > removing the symbol first, not allowing to enable it. Should nothing > happening within the next half year, lets remove code bits around August > after the summer break. >=20 > Signed-off-by: Sebastian Andrzej Siewior > --- I'm not saying that there's a lot of users, and it may still be worth=20 eliminating it, but PLD Linux has actively supported x86_64 with x32 ABI fo= r=20 well over a decade now. They maintain a patchset on RPM to expose this=20 properly (and I've attempted to create better versions for upstreaming[1][2= ],=20 and there was a third attempt[3] too). So it isn't broadly used indeed, but it's used enough that it's probably wo= rth=20 being slightly more careful about deciding to remove it. [1]: https://github.com/rpm-software-management/rpm/pull/360 [2]: https://github.com/rpm-software-management/rpm/pull/1038 [3]: https://github.com/rpm-software-management/rpm/pull/3578 =2D-=20 =E7=9C=9F=E5=AE=9F=E3=81=AF=E3=81=84=E3=81=A4=E3=82=82=E4=B8=80=E3=81=A4=EF= =BC=81/ Always, there's only one truth!