linux-kernel - Re: kernel/fork.c:3088:2: warning: clone3() entry point is missing, please fix

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Message-Id: <46c6b0f6-6155-4366-9cbf-9fbbfb95ce30@app.fastmail.com>
Date: Mon, 30 Jun 2025 12:02:39 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "John Paul Adrian Glaubitz" <glaubitz@...sik.fu-berlin.de>,
 "kernel test robot" <lkp@...el.com>
Cc: llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
 linux-kernel@...r.kernel.org, linux-hexagon@...r.kernel.org,
 sparclinux@...r.kernel.org, linux-sh@...r.kernel.org,
 "Dinh Nguyen" <dinguyen@...nel.org>,
 "Simon Schuster" <schuster.simon+binutils@...mens-energy.com>,
 Linux-Arch <linux-arch@...r.kernel.org>,
 "Christian Brauner" <brauner@...nel.org>
Subject: Re: kernel/fork.c:3088:2: warning: clone3() entry point is missing, please fix

On Mon, Jun 30, 2025, at 08:30, John Paul Adrian Glaubitz wrote:
> On Mon, 2025-06-30 at 08:14 +0200, Arnd Bergmann wrote:
>> On Sat, Jun 28, 2025, at 21:59, kernel test robot wrote:
>> 
>> I don't think any of those architecture maintainers are paying
>> attention to the build warnings or the lkp reports, and they are
>> clearly not trying to fix them any more, so maybe it's better to
>> just stop testing them in lkp.
>
> I have seen that warning about clone3() missing but I was not aware that it's
> an urgent issue to address. Do you have any suggestion on how to implement
> that syscall?

Some architectures have custom calling conventions for the
fork/vfork/clone/clone3 syscalls, e.g. to handle copying all the
registers correctly when the normal syscall entry doesn't do that,
or to handle the changing stack correctly.

I see that both sparc and hexagon have a custom clone() syscall,
so they likely need a custom clone3() as well, while sh and
nios2 probably don't.

All four would need a custom assembler implementation in userspace
for each libc, in order to test the userspace calling the clone3()
function. For testing the kernel entry point itself, see Christian's
original test case[1].

     Arnd

[1] https://lore.kernel.org/lkml/20190716130631.tohj4ub54md25dys@brauner.io/