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Message-ID: <20260725132734.GG3520958@port70.net>
Date: Sat, 25 Jul 2026 15:27:34 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: James Y Knight <jyknight@...gle.com>
Cc: musl@...ts.openwall.com, Jake Adamson <jakeadamson@...gle.com>,
Peter Oskolkov <posk@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
mathieu.desnoyers@...icios.com
Subject: Re: Re: Question: number of arguments of musl's membarrier
does not match Linux syscall
* James Y Knight <jyknight@...gle.com> [2026-07-24 18:06:45 -0400]:
> But it's not a breakage to add another arg to a syscall which is only
> looked at when a newly-introduced flag is passed in the existing arg.
>
> While it might be nice if the kernel expressed opinions as to how syscalls
> ought to be wrapped with userspace C functions, there's no actual problem
> with that _as a syscall change_.
>
> E.g., libc implementations could, if they wished, simply add a brand-new
> wrapper function, membarrier3(int, unsigned, int), which still invokes the
> same syscall number as the 2-arg "membarrier(int, unsigned)". It's really
> just a matter of documentation and agreement between the various userspace
that agreement is the man page, which got changed.
> libc implementations here as to what they wish a wrapper function to look
> like, not any issue on the kernel side.
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