linux-kernel - Re: [PATCH] RISC-V: Include clone3() on rv32

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Date:   Mon, 04 Oct 2021 17:35:40 -0700 (PDT)
From:   Palmer Dabbelt <palmerdabbelt@...gle.com>
To:     christian.brauner@...ntu.com
CC:     Arnd Bergmann <arnd@...db.de>, linux-riscv@...ts.infradead.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, christian@...uner.io,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject:     Re: [PATCH] RISC-V: Include clone3() on rv32

On Mon, 04 Oct 2021 04:17:58 PDT (-0700), christian.brauner@...ntu.com wrote:
> On Sun, Oct 03, 2021 at 05:30:24PM +0200, Arnd Bergmann wrote:
>> On Sun, Oct 3, 2021 at 2:58 AM Palmer Dabbelt <palmer@...belt.com> wrote:
>> >
>> > From: Palmer Dabbelt <palmerdabbelt@...gle.com>
>> >
>> > As far as I can tell this should be enabled on rv32 as well, I'm not
>> > sure why it's rv64-only.  checksyscalls is complaining about our lack of
>> > clone3() on rv32.
>> >
>> > Fixes: 56ac5e213933 ("riscv: enable sys_clone3 syscall for rv64")
>> > Signed-off-by: Palmer Dabbelt <palmerdabbelt@...gle.com>
>>
>> We should probably reverse the polarity of this symbol and force
>> architectures that don't implement it properly to say they don't
>> have it, but for now, it definitely makes sense to treat this the same
>> way on 32-bit and 64-bit risc-v.
>
> I think we had that discussion back when I added it and I think I even
> proposed that or you did but then we settled on __ARCH_WANT_SYS_CLONE3.
> Most likely because it fell in line with the other
> __ARCH_WANT_SYS_{CLONE,FORK}.
>
> I think at this point its alpha, ia64, nios, sparc, and sh that don't
> implement it. For some it looks trivial at first glance at least (Fwiw,
> nios implements sys_clone() but doesn't select __ARCH_WANT_SYS_CLONE3):
>
> diff --git a/arch/nios2/include/uapi/asm/unistd.h b/arch/nios2/include/uapi/asm/unistd.h
> index 0b4bb1d41b28..6c4f45abd3ab 100644
> --- a/arch/nios2/include/uapi/asm/unistd.h
> +++ b/arch/nios2/include/uapi/asm/unistd.h
> @@ -18,6 +18,7 @@
>
>   #define sys_mmap2 sys_mmap_pgoff
>
> +#define __ARCH_WANT_SYS_CLONE3
>  #define __ARCH_WANT_RENAMEAT
>  #define __ARCH_WANT_STAT64
>  #define __ARCH_WANT_SET_GET_RLIMIT
> diff --git a/arch/nios2/kernel/entry.S b/arch/nios2/kernel/entry.S
> index 0794cd7803df..c1804bda8259 100644
> --- a/arch/nios2/kernel/entry.S
> +++ b/arch/nios2/kernel/entry.S
> @@ -396,6 +396,15 @@ ENTRY(sys_clone)
>         RESTORE_SWITCH_STACK
>         ret
>
> +/*
> + * int clone3(struct clone_args __user *, uargs, size_t, size)
> + */
> +ENTRY(sys_clone3)
> +       SAVE_SWITCH_STACK
> +       call    sys_clone3
> +       RESTORE_SWITCH_STACK
> +       ret
> +
>  ENTRY(sys_rt_sigreturn)
>         SAVE_SWITCH_STACK
>         mov     r4, sp

Thanks.

I've put this on fixes, but if you're trying to do that refactoring I've 
merged it in as a single patch on top of 5.15-rc1.  That's on 
palmer/riscv-clone3, in case it helps someone avoid a conflict when 
doing that refactoring.  I'd usually offer to do the refactoring, but 
I'm super buried right now with all the RISC-V stuff ;)

I want to call this fix because it's breaking my builds, these 
checksyscall warnings have recently turned into errors.