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

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Message-ID: <6d0659c3-fd86-4eab-879f-d9b149462358@gmail.com>
Date: Thu, 30 Jan 2025 22:46:26 +0800
From: Ism Hong <ism.hong@...il.com>
To: Arnd Bergmann <arnd@...db.de>
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

Arnd Bergmann 於 2025/1/28 清晨5:20 寫道:
> 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

Hi Arnd,

Thank you for your explanation, and sorry for the late reply due to the 
Chinese New Year.

 From your response, I understand that the preferred solution would be 
to modify uClibc to align the behavior of semctl/shmctl/msgctl with 
glibc and musl by adopting a unified feature test macro. If that is the 
case, I will work on preparing a patch for uClibc accordingly.

Please let me know if you have any suggestions or if I have 
misunderstood anything.

Thanks,
Ism