linux-kernel - Re: [PATCH v2] x86/boot/64/clang: Use fixup_pointer() to access '__supported_pte

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Message-ID: <a67943d1-f7e8-c465-ce8d-a9c9a0a6f653@linux.intel.com>
Date:   Tue, 8 May 2018 09:49:39 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Alexander Potapenko <glider@...gle.com>, mingo@...nel.org,
        kirill.shutemov@...ux.intel.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org, mka@...omium.org,
        dvyukov@...gle.com, md@...gle.com
Subject: Re: [PATCH v2] x86/boot/64/clang: Use fixup_pointer() to access
 '__supported_pte_mask'

On 05/08/2018 09:28 AM, 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().

Looks good to me.  Thanks for adding the comment, especially!

Reviewed-by: Dave Hansen <dave.hansen@...el.com>