linux-kernel - Re: [PATCH v2 1/4] x86/vdso: Remove obsolete "fake section table" reservation

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Message-ID: <CALCETrVZraOwkdjtVLdOk4+t4Z0i6ThcWzjK5pjee1djS8CD9w@mail.gmail.com>
Date:   Tue, 4 Dec 2018 14:48:54 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     "Christopherson, Sean J" <sean.j.christopherson@...el.com>
Cc:     Andrew Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/4] x86/vdso: Remove obsolete "fake section table" reservation

On Tue, Dec 4, 2018 at 1:26 PM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> At one point the vDSO image was manually stripped down by vdso2c in an
> attempt to minimize the size of the image mapped into userspace.  Part
> of that stripping process involved building a fake section table so as
> not to break userspace processes that parse the section table.  Memory
> for the fake section table was reserved in the .rodata section so that
> vdso2c could simply copy the entire PT_LOAD segment into the userspace
> image after building the fake table.
>
> Eventually, the entire fake section table approach was dropped in favor
> of stripping the vdso "the old fashioned way", i.e. via objdump -S.
> But, the reservation in .rodata for the fake table was left behind.
> Remove the reserveration along with a few other related defines and
> section entries.
>
> Removing the fake section table placeholder zaps a whopping 0x340 bytes
> from the 64-bit vDSO image, which drops the current image's size to
> under 4k, i.e. reduces the effective size of the userspace vDSO mapping
> by a full page.

Acked-by: Andy Lutomirski <luto@...nel.org>