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From:   Thomas Gleixner <tglx@linutronix.de>
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To:     Andy Lutomirski <luto@kernel.org>, x86@kernel.org
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Brian Gerst <brgerst@gmail.com>,
        Andy Lutomirski <luto@kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH v4 3/9] x86/entry: Convert ret_from_fork to C
In-Reply-To: <f7ed7fa5b222afa2d2820e1d8c83fdc3fdd57af2.1616004689.git.luto@kernel.org>
References: <cover.1616004689.git.luto@kernel.org> <f7ed7fa5b222afa2d2820e1d8c83fdc3fdd57af2.1616004689.git.luto@kernel.org>
Date:   Fri, 19 Mar 2021 17:05:27 +0100
Message-ID: <87v99n5dtk.fsf@nanos.tec.linutronix.de>
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On Wed, Mar 17 2021 at 11:12, Andy Lutomirski wrote:

> ret_from_fork is written in asm, slightly differently, for x86_32 and
> x86_64.  Convert it to C.
> +__visible void noinstr ret_from_fork(struct task_struct *prev,
> +				     int (*kernel_thread_fn)(void *),
> +				     void *kernel_thread_arg,
> +				     struct pt_regs *user_regs)
> +{
> +	instrumentation_begin();
> +
> +	schedule_tail(prev);
> +
> +	if (kernel_thread_fn) {
> +		kernel_thread_fn(kernel_thread_arg);
> +		user_regs->ax = 0;

If you replace this with:

   syscall_set_return_value(current, user_regs, 0, 0);

then it's architecture agnostic and can move to kernel/entry, no?

Thanks,

        tglx