linux-kernel - Re: [RFC PATCH v1 0/8] nolibc signal handling support

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Date:   Thu, 29 Dec 2022 18:41:59 +0700
From:   Ammar Faizi <ammarfaizi2@...weeb.org>
To:     Willy Tarreau <w@....eu>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Gilang Fachrezy <gilang4321@...il.com>,
        VNLX Kernel Department <kernel@...x.org>,
        Alviro Iskandar Setiawan <alviro.iskandar@...weeb.org>,
        Kanna Scarlet <knscarlet@...weeb.org>,
        Muhammad Rizki <kiizuha@...weeb.org>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kselftest Mailing List 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [RFC PATCH v1 0/8] nolibc signal handling support

On 12/28/22 8:35 PM, Willy Tarreau wrote:
> OK thanks!
> 
> I've pushed for you an update which starts to do what I proposed. Errno
> and environ are now marked weak for all archs, and _auxv is set for i386,
> x86_64, arm64 and arm for now:
> 
>     https://git.kernel.org/pub/scm/linux/kernel/git/wtarreau/nolibc.git/log/?h=20221227-nolibc-weak-2
> 
> You can already use it to implement getauxval(), it will normally work
> for these archs.

Will do and be back with two patch series.

> I think we could avoid the asm specific stuff is we get rid of the frame
> pointer. Please look below:
> 
>    __attribute__((weak,unused,noreturn,optimize("omit-frame-pointer"),section(".text.nolibc_rt_sigreturn")))
>    void sys_rt_sigreturn()
>    {
>          my_syscall0(__NR_rt_sigreturn);
>          __builtin_unreachable();
>    }

Wow! You just taught me that we can force optimize a function with
optimize("omit-frame-pointer") attribute. Nice to know this one!

I compile-tested it and it indeed gives the correct code on x86-64.
Hopefully this approach works for all archs.

> It gives me the correct code for x86_64 and i586. I don't know if other
> architectures will want to add a prologue. I tried with "naked" but it's
> ignored by the compiler since the function is not purely asm. Not very
> important but given that we already have everything to perform our calls
> it would make sense to stay on this. By the way, for the sake of
> consistency with other syscalls, I do think the function (or label if
> we can't do otherwise) should be called "sys_rt_sigreturn" as it just
> performs a syscall.

Will call that 'sys_rt_sigreturn' in the next series.

Thanks!

-- 
Ammar Faizi