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: <835459920.20630.1589420674977.JavaMail.zimbra@efficios.com>
Date:   Wed, 13 May 2020 21:44:34 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     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 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 ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com