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Re: [RFC 20/22] x86/relocs: Add option to generate 64-bit relocations

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<cmetcalf@mellanox.com>,"Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,Andrew Morton <akpm@linux-foundation.org>,Christopher Li <sparse@chrisli.org>,Dou Liyang <douly.fnst@cn.fujitsu.com>,Masahiro Yamada <yamada.masahiro@socionext.com>,Daniel Borkmann <daniel@iogearbox.net>,Markus Trippelsdorf <markus@trippelsdorf.de>,Peter Foley <pefoley2@pefoley.com>,Steven Rostedt <rostedt@goodmis.org>,Tim Chen <tim.c.chen@linux.intel.com>,Ard Biesheuvel <ard.biesheuvel@linaro.org>,Catalin Marinas <catalin.marinas@arm.com>,Matthew Wilcox <mawilcox@microsoft.com>,Michal Hocko <mhocko@suse.com>,Rob Landley <rob@landley.net>,Jiri Kosina <jkosina@suse.cz>,"H . J . Lu" <hjl.tools@gmail.com>,Paul Bolle <pebolle@tiscali.nl>,Baoquan He <bhe@redhat.com>,Daniel Micay <danielmicay@gmail.com>,the arch/x86 maintainers <x86@kernel.org>,linux-crypto@vger.kernel.org,LKML <linux-kernel@vger.kernel.org>,xen-devel@lists.xenproject.org,kvm list <kvm@vger.kernel.org>,Linux PM list
<linux-pm@vger.kernel.org>,linux-arch <linux-arch@vger.kernel.org>,linux-sparse@vger.kernel.org,Kernel Hardening <kernel-hardening@lists.openwall.com>
From: hpa@zytor.com
Message-ID: <0EF6FAAA-A99C-4F0D-9E4A-AD25E93957FB@zytor.com>

On July 19, 2017 4:25:56 PM PDT, Thomas Garnier <thgarnie@google.com> wrote:
>On Wed, Jul 19, 2017 at 4:08 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>> On 07/19/17 15:47, Thomas Garnier wrote:
>>> On Wed, Jul 19, 2017 at 3:33 PM, H. Peter Anvin <hpa@zytor.com>
>wrote:
>>>> On 07/18/17 15:33, Thomas Garnier wrote:
>>>>> The x86 relocation tool generates a list of 32-bit signed
>integers. There
>>>>> was no need to use 64-bit integers because all addresses where
>above the 2G
>>>>> top of the memory.
>>>>>
>>>>> This change add a large-reloc option to generate 64-bit unsigned
>integers.
>>>>> It can be used when the kernel plan to go below the top 2G and
>32-bit
>>>>> integers are not enough.
>>>>
>>>> Why on Earth?  This would only be necessary if the *kernel itself*
>was
>>>> more than 2G, which isn't going to happen for the forseeable
>future.
>>>
>>> Because the relocation integer is an absolute address, not an offset
>>> in the binary. Next iteration, I can try using a 32-bit offset for
>>> everyone.
>>
>> It is an absolute address *as the kernel was originally linked*, for
>> obvious reasons.
>
>Sure when the kernel was just above 0xffffffff80000000, it doesn't
>work when it goes down to 0xffffffff00000000. That's why using an
>offset might make more sense in general.
>
>>
>>         -hpa
>>

What is the motivation for changing the pre linked address at all?
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

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Re: [RFC 20/22] x86/relocs: Add option to generate 64-bit relocations "H. Peter Anvin" <hpa@zytor.com> - 2017-07-20 02:20 +0200

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