linux-kernel - Re: [PATCH] mips: fix shmctl/semctl/msgctl syscall for o32

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Message-Id: <5427df64-658d-4377-89be-963ee7bb68ee@app.fastmail.com>
Date: Mon, 27 Jan 2025 22:20:49 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Ism Hong" <ism.hong@...il.com>
Cc: "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
 "Christian Brauner" <brauner@...nel.org>,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "Heiko Carstens" <hca@...ux.ibm.com>, "Jeff Xu" <jeffxu@...omium.org>,
 Christian Göttsche <cgzones@...glemail.com>,
 "open list:MIPS" <linux-mips@...r.kernel.org>,
 "open list" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mips: fix shmctl/semctl/msgctl syscall for o32

On Mon, Jan 6, 2025, at 12:52, Ism Hong wrote:
> The commit 275f22148e87 ("ipc: rename old-style shmctl/semctl/msgctl
> syscalls") switched various architectures to use sys_old_*ctl() with
> ipc_parse_version, including mips n32/n64. However, for mips o32, commit
> 0d6040d46817 ("arch: add split IPC system calls where needed") added
> separate IPC syscalls without properly using the old-style handlers.
>
> This causes applications using uClibc-ng to fail with -EINVAL when
> calling semctl/shmctl/msgctl with IPC_64 flag, as uClibc-ng uses the
> syscall numbers from kernel headers to determine whether to use the IPC
> multiplexer or split syscalls. In contrast, glibc is unaffected as it
> uses a unified feature test macro __ASSUME_DIRECT_SYSVIPC_SYSCALLS
> (disabled for mips-o32) to make this decision.
>
> Fix this by switching the o32 ABI entries for semctl, shmctl and msgctl
> to use the old-style handlers, matching the behavior of other
> architectures and fixing compatibility with uClibc-ng.
>
> Signed-off-by: Ism Hong <ism.hong@...il.com>

I just saw this making it into mainline and had another look, sorry
I hadn't caught it earlier.

It was an intentional decision to use the new-style IPC_64
semantics on architectures that didn't already have the
separate system call.

You may not like that choice, but it's been done this way
for seven years now, and as far as I can tell, glibc relies
on this behavior.

I think this commit should be reverted, and uclibc be changed
to implement the kernel ABI for these syscalls.

      Arnd