Re: [PATCH] x86: Start removing X86_X32_ABI

[Neal Gompa]

On Saturday, May 23, 2026 5:37:34 AM Eastern Daylight Time 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.
> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---

I'm not saying that there's a lot of users, and it may still be worth 
eliminating it, but PLD Linux has actively supported x86_64 with x32 ABI for 
well over a decade now. They maintain a patchset on RPM to expose this 
properly (and I've attempted to create better versions for upstreaming[1][2], 
and there was a third attempt[3] too).

So it isn't broadly used indeed, but it's used enough that it's probably worth 
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


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