linux-kernel - Re: [PATCH v6 02/27] x86: Use symbol name in jump table for PIE support

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Message-ID: <20190207171145.GH2414@zn.tnic>
Date:   Thu, 7 Feb 2019 18:11:45 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Garnier <thgarnie@...omium.org>
Cc:     Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Nadav Amit <namit@...are.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 02/27] x86: Use symbol name in jump table for PIE
 support

On Thu, Feb 07, 2019 at 09:04:45AM -0800, Thomas Garnier wrote:
> I assume that's an optimisation done by gcc later.

So why is that change even needed? Where does it break?

> The P modifier in the documentation does state that it is used to
> generate PIC code.

The documentation says:

"If used for a function, print the PLT suffix and generate PIC code. For
example, emit foo@PLT instead of ’foo’ for the function foo()."

when you use %P for a function. Which is not how it is used here.

-- 
Regards/Gruss,
    Boris.

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