linux-kernel - Re: [PATCH] x86/vdso: drop implicit common-page-size linker flag

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Message-ID: <CALCETrUu5TuNQ9rxtpRng3=r4eaJQMs4PTNR6s=VFPKfW7eNBQ@mail.gmail.com>
Date:   Thu, 6 Dec 2018 12:29:42 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Andrew Lutomirski <luto@...nel.org>, maskray@...gle.com,
        Andi Kleen <ak@...ux.intel.com>,
        Andi Kleen <andi@...stfloor.org>, dima@...ovin.in,
        morbo@...gle.com, ruiu@...gle.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/vdso: drop implicit common-page-size linker flag

On Thu, Dec 6, 2018 at 11:12 AM <ndesaulniers@...gle.com> wrote:
>
> These are implied by the target architecture and for x86_64 match the
> max-page-size. The default for non-NaCl x86_64 is 0x1000 (4096).
>
> In bfd the common page size is defined as 0x1000 (4096) for non-NaCl
> x86_64 targets:
>
> bfd/elf64-x86-64.c:
> 4998:#define ELF_COMMONPAGESIZE             0x1000
>
> For gold, the common page size is defined as 0x1000 (4096) for non-NaCl
> x86_64 targets:
>
> gold/x86_64.cc:
> 1413:  0x1000, // common_pagesize (overridable by -z common-page-size)
> 1442:  0x1000, // common_pagesize (overridable by -z common-page-size)
>
> (ELF_COMMONPAGESIZE also defaults to ELF_MAXPAGESIZE when not set
> explicitly for a target architecture in bfd/elfxx-target.h, but that's
> not relevant for x86_64).
>
> Because it's implied by the target architecture, it's of questionable
> use to implement in LLD.  This patch resolves one of the issues towards
> using LLD to link an x86_64 kernel.

Sure.

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