linux-kernel - Re: [patch V4 part 3 09/29] x86/entry/32: Provide macro to emit IDT entry stubs

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Message-ID: <CALCETrXFv59dX5K5R_KO6D5uznD9E8DCDR5fQ7_fCwTTGOgS5Q@mail.gmail.com>
Date:   Wed, 13 May 2020 21:31:32 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, paulmck <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>, rostedt <rostedt@...dmis.org>,
        "Joel Fernandes, Google" <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 3 09/29] x86/entry/32: Provide macro to emit IDT
 entry stubs

On Wed, May 13, 2020 at 6:44 PM Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
>
> ----- On May 5, 2020, at 9:44 AM, Thomas Gleixner tglx@...utronix.de wrote:
>
> [...]
>
> > +.macro idtentry vector asmsym cfunc has_error_code:req sane=0
> > +SYM_CODE_START(\asmsym)
> > +     ASM_CLAC
> > +     cld
>
> Looking at the various interrupt and trap entry points for 32 and 64-bit
> x86, I notice a lack of consistency in use of the following instruction
> sequence at the asm entry point:
>
> - ASM_CLAC,
> - cld (clear direction flag).
>
> Are they always needed, or only for interrupt handlers ?

They're needed for all entries except SYSCALL, but they're hidden
inside helpers in many cases.