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

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Message-ID: <20250701-packung-zweifach-49a0189a1dea@brauner>
Date: Tue, 1 Jul 2025 10:49:27 +0200
From: Christian Brauner <brauner@...nel.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>, 
	kernel test robot <lkp@...el.com>, 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>
Subject: Re: kernel/fork.c:3088:2: warning: clone3() entry point is missing,
 please fix

On Mon, Jun 30, 2025 at 02:07:58PM +0200, Arnd Bergmann wrote:
> On Mon, Jun 30, 2025, at 12:45, John Paul Adrian Glaubitz wrote:
> > On Mon, 2025-06-30 at 12:02 +0200, Arnd Bergmann wrote:
> >> 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].
> >
> > Thanks for the explanation. So, I guess as long as a proposed implementation
> > of clone3() on sh would pass Arnd's test program, it should be good for merging?
> 
> Yes, Christian's test program should be enough for merging into
> the kernel, though I would recommend also coming up with the matching
> glibc patch, in order to ensure it can actually be regression tested
> automatically, and to use the new features provided by glibc clone3().

Note that we do have clone3() selftests in the kernel:

> ls -al tools/testing/selftests/clone3/
total 48
drwxrwxr-x   2 brauner brauner   175 Jun  4 22:45 .
drwxrwxr-x 118 brauner brauner  4096 Jun 16 10:10 ..
-rw-rw-r--   1 brauner brauner  7377 Apr 15 10:47 clone3.c
-rw-rw-r--   1 brauner brauner  3939 May 13 12:23 clone3_cap_checkpoint_restore.c
-rw-rw-r--   1 brauner brauner  2512 Apr 15 10:47 clone3_clear_sighand.c
-rw-rw-r--   1 brauner brauner  1437 Jun  4 22:45 clone3_selftests.h
-rw-rw-r--   1 brauner brauner 10738 Apr 15 10:47 clone3_set_tid.c
-rw-rw-r--   1 brauner brauner   113 Apr 11 15:36 .gitignore
-rw-rw-r--   1 brauner brauner   206 Apr 15 10:47 Makefile