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Message-ID: <amKTgOA68fL1T83u@google.com>
Date: Thu, 23 Jul 2026 15:23:22 -0700
From: Nick Desaulniers <ndesaulniers@...gle.com>
To: Szabolcs Nagy <nsz@...t70.net>
Cc: Jake Adamson <jakeadamson@...gle.com>, musl@...ts.openwall.com,
Peter Oskolkov <posk@...gle.com>, Peter Zijlstra <peterz@...radead.org>,
mathieu.desnoyers@...icios.com
Subject: Re: Question: number of arguments of musl's membarrier does not
match Linux syscall
On Thu, Jul 23, 2026 at 11:34:51PM +0200, Szabolcs Nagy wrote:
> * Jake Adamson <jakeadamson@...gle.com> [2026-07-23 13:34:02 -0700]:
> > Hi I'm adding membarrier() to Android's Bionic and I noticed that
> > there are a different number of arguments in Musl than in Linux’s
> > system call. Is there a reason for that and is there any nuisance that
> > I should be thinking about when adding it? And do you plan on adding
> > the cpu_id argument?
>
> google broke it (silently)
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2a36ab717e8fe678d98f81c14a0b124712719840
Oops, did it get reported, yet?
I didn't see any follow ups one the original LKML thread.
https://lore.kernel.org/all/20200923233618.2572849-1-posk@google.com/T/#u
Patch from 2020...perhaps too late to do anything about it. Though shall
not break userspace...
>
> good example why libc does not like wrapping new syscalls
> (the contract is not documented and reasonable assumptions
> get broken instead of using a new syscall number)
>
> now it has to be var arg if we want backward compat.
>
> >
> > Linux: int cmd, unsigned int flags, int cpu_id
> > https://man7.org/linux/man-pages/man2/membarrier.2.html
> >
> >
> > Musl: int cmd, int flags
> > https://git.musl-libc.org/cgit/musl/tree/src/linux/membarrier.c
> >
> > Jake Adamson
> > Android Native Tools and Libraries, Software Engineer
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