linux-kernel - Re: [RFC PATCH v3 1/6] x86/entry/64: move PUSH_AND_CLEAR_REGS from interrupt macro to helper function

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Message-ID: <CA+55aFx=moDaKj3Ogc_Fvm0vKQ1DP=yA9UE3axmpECyv3Khi1Q@mail.gmail.com>
Date:   Tue, 20 Feb 2018 14:25:03 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Dominik Brodowski <linux@...inikbrodowski.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Brian Gerst <brgerst@...il.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [RFC PATCH v3 1/6] x86/entry/64: move PUSH_AND_CLEAR_REGS from
 interrupt macro to helper function

On Tue, Feb 20, 2018 at 1:01 PM, Dominik Brodowski
<linux@...inikbrodowski.net> wrote:
> +ENTRY(interrupt_entry)
> +       UNWIND_HINT_FUNC
> +
> +       PUSH_AND_CLEAR_REGS save_ret=1
> +       ENCODE_FRAME_POINTER 8
> +
> +       ret
> +END(interrupt_entry)

There's nothing wrong with this patch, but it does expose what a nasty
hack our "ENCODE_FRAME_POINTER" thing is.

It generates (when there is an offset, like this):

        leaq \ptregs_offset(%rsp), %rbp
        orq     $0x1, %rbp

and I would _really_ hope that the stack pointer is always aligned on
interrupt entry, so I don't see why it's not just

        leaq 1+\ptregs_offset(%rsp), %rbp

instead.

I dunno. Let's ask Josh what the reason for the separate "or" was.

But this is an independent issue of this patch, really.

              Linus