Re: [PATCH] x86: Start removing X86_X32_ABI

[John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>]

Hello Sebastian,

On Sat, 2026-05-23 at 11:37 +0200, Sebastian Andrzej 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.
> 
> 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).
> 
> 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.
> 
> 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.

Debian still has an x32 port which is building unstable packages, see [1].

Even Rust works there.

Adrian

> [1] https://buildd.debian.org/status/architecture.php?a=x32&suite=sid

-- 
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