linux-kernel - Re: [PATCH V2 16/41] x86/entry: Implement the whole error

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Date:   Wed, 29 Sep 2021 10:45:17 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Brian Gerst <brgerst@...il.com>
Cc:     Lai Jiangshan <jiangshanlai@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Youquan Song <youquan.song@...el.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH V2 16/41] x86/entry: Implement the whole error_entry() as
 C code

On Tue, Sep 28, 2021 at 05:34:02PM -0400, Brian Gerst wrote:
> On Sun, Sep 26, 2021 at 11:13 AM Lai Jiangshan <jiangshanlai@...il.com> wrote:
> > +asmlinkage __visible __entry_text
> > +struct pt_regs *error_entry(struct pt_regs *eregs)
> > +{
> > +       unsigned long iret_ip = (unsigned long)native_irq_return_iret;
> > +
> > +       asm volatile ("cld");
> 
> The C ABI states that the direction flag must be clear on function
> entry and exit, so the CLD instruction needs to remain in the asm
> code.

Right, also, one of my pet peeves with out entry code is that CLD and
CLAC are not next to one another.