linux-kernel - Re: [PATCH v3] x86/boot/64/clang: Use fixup_pointer() to access '__supported_pte

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Message-ID: <20180511074337.3fa5htarfcsbeeqy@kshutemo-mobl1>
Date:   Fri, 11 May 2018 10:43:37 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     dave.hansen@...ux.intel.com, mingo@...nel.org,
        kirill.shutemov@...ux.intel.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, mka@...omium.org, dvyukov@...gle.com,
        md@...gle.com
Subject: Re: [PATCH v3] x86/boot/64/clang: Use fixup_pointer() to access
 '__supported_pte_mask'

On Wed, May 09, 2018 at 11:18:22AM +0200, Alexander Potapenko wrote:
> Clang builds with defconfig started crashing after commit fb43d6cb91ef
> ("x86/mm: Do not auto-massage page protections")
> This was caused by introducing a new global access in __startup_64().
> 
> Code in __startup_64() can be relocated during execution, but the compiler
> doesn't have to generate PC-relative relocations when accessing globals
> from that function. Clang actually does not generate them, which leads
> to boot-time crashes. To work around this problem, every global pointer
> must be adjusted using fixup_pointer().
> 
> Signed-off-by: Alexander Potapenko <glider@...gle.com>
> Fixes: fb43d6cb91ef ("x86/mm: Do not auto-massage page protections")

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
 Kirill A. Shutemov