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Re: [committed, PATCH] Add -mshared option to x86 ELF assembler
- From: Andy Lutomirski <luto at amacapital dot net>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>, X86 ML <x86 at kernel dot org>, "linux-kernel at vger dot kernel dot org" <linux-kernel at vger dot kernel dot org>
- Cc: Markus Trippelsdorf <markus at trippelsdorf dot de>, Binutils <binutils at sourceware dot org>, Andy Lutomirski <luto at kernel dot org>
- Date: Mon, 1 Jun 2015 08:48:48 -0700
- Subject: Re: [committed, PATCH] Add -mshared option to x86 ELF assembler
- Authentication-results: sourceware.org; auth=none
- References: <20150515103414 dot GA20518 at intel dot com> <20150601083214 dot GA381 at x4> <CAMe9rOrdqc1v7Dzm3T=CO2a7mVNypOXkAZMFxRMJwwcu61jxGQ at mail dot gmail dot com>
On Mon, Jun 1, 2015 at 4:05 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Jun 1, 2015 at 1:32 AM, Markus Trippelsdorf
> <markus@trippelsdorf.de> wrote:
>> On 2015.05.15 at 03:34 -0700, H.J. Lu wrote:
>>> This patch adds -mshared option to x86 ELF assembler. By default,
>>> assembler will optimize out non-PLT relocations against defined non-weak
>>> global branch targets with default visibility. The -mshared option tells
>>> the assembler to generate code which may go into a shared library
>>> where all non-weak global branch targets with default visibility can
>>> be preempted. The resulting code is slightly bigger. This option
>>> only affects the handling of branch instructions.
>>>
>>> This Linux kernel patch is needed to create a working x86 Linux kernel if
>>> it hasn't been applied:
>>>
>>> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
>>> index ae6588b..b91a00c 100644
>>> --- a/arch/x86/kernel/head_64.S
>>> +++ b/arch/x86/kernel/head_64.S
>>> @@ -339,8 +339,8 @@ early_idt_handlers:
>>> i = i + 1
>>> .endr
>>>
>>> -/* This is global to keep gas from relaxing the jumps */
>>> -ENTRY(early_idt_handler)
>>> +/* This is weak to keep gas from relaxing the jumps */
>>> +WEAK(early_idt_handler)
>>> cld
>>
>> Have you posted the patch to LKML already?
>> (I hit this issue today and it took me a while to figure out the cause.)
>
> A kernel patch will be checked in soon.
>
It already is:
https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?h=x86/asm&id=cdeb6048940fa4bfb429e2f1cba0d28a11e20cd5
It's currently queued for 4.2.
Ingo, would it make sense to promote this to 4.1? It's definitely a
violation of the "no development after the merge window" rule, but
it's sort of a build fix. Alternatively, we could ask Greg et al to
backport it.
--Andy