linux-kernel - Re: "." in vmlinux.lds.S

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Date:	Fri, 6 Jun 2014 13:45:14 -0700
From:	Hán Shěn (沈涵) <shenhan@...gle.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>
Subject: Re: "." in vmlinux.lds.S

Hi Andy, this changes "Ndx" field for the symbol. For example, one of
the symbol '__end_rodata_hpage_align' in symtab, the contents changed
from
    50206: ffffffff81800000     0 NOTYPE  GLOBAL DEFAULT  ABS
__end_rodata_hpage_align
which is correct, to
    50206: ffffffff81800000     0 NOTYPE  GLOBAL DEFAULT   25
__end_rodata_hpage_align
(25 is the index to section '.data')
which is wrong.

Han



On Fri, Jun 6, 2014 at 12:08 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Fri, Jun 6, 2014 at 11:53 AM, Hán Shěn (沈涵) <shenhan@...gle.com> wrote:
>> Yeah, the symbol "__end_rodata_hpage_align" is defined as absolute in
>> older binutils, the newer binutils making it relative seems
>> meaningless in this context.
>
> What I mean is: what actually changes in the linker output when the
> symbol is relative?
>
> --Andy
>
>>
>> On Fri, Jun 6, 2014 at 11:40 AM, Andy Lutomirski <luto@...capital.net> wrote:
>>> On 06/06/2014 10:08 AM, Hán Shěn (沈涵) wrote:
>>>> A gentle ping?
>>>>
>>>> On Tue, Jun 3, 2014 at 2:46 PM, Hán Shěn (沈涵) <shenhan@...gle.com> wrote:
>>>>> Hi we are trying to boot up a x86_64 chrome book using binutils 2.24 and
>>>>> kernel 3.8, but failed.
>>>>>
>>>>> After some triage work, we found that a 2-year-old binutil CL changed the
>>>>> interpretation of "." in linker script （short story: absolute -> relative,
>>>>> long story: https://sourceware.org/ml/binutils/2012-06/msg00155.html).
>>>>>
>>>>> After some further work, we are able to boot the kernel with a kernel patch
>>>>> pasted at EOM. I am curious, why the upstream kernel is never hit by this
>>>>> behavior? We enabled "CONFIG_DEBUG_RODATA", so we were hit, is this some
>>>>> macro not usually turned on?
>>>
>>> What does a section-relative symbol do?
>>>
>>> --Andy
>>
>>
>>
>> --
>> Han Shen |  Software Engineer |  shenhan@...gle.com |  +1-650-440-3330
>
>
>
> --
> Andy Lutomirski
> AMA Capital Management, LLC



-- 
Han Shen |  Software Engineer |  shenhan@...gle.com |  +1-650-440-3330
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