linux-kernel - Re: [PATCH] blackfin: Makefile: Skip reloc overflow issue when COMPILE

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Message-ID: <CAMk6uB=pZSMd1ADtMUq0gGHe0zxSYHDN2Fy_VFxw-xE4vr1weQ@mail.gmail.com>
Date:	Fri, 24 Apr 2015 16:20:37 +0800
From:	Steven Miao <realmz6@...il.com>
To:	Chen Gang <xili_gchen_5257@...mail.com>
Cc:	Richard Weinberger <richard.weinberger@...il.com>,
	bfin <adi-buildroot-devel@...ts.sourceforge.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] blackfin: Makefile: Skip reloc overflow issue when
 COMPILE_TEST enabled

On Thu, Apr 23, 2015 at 10:30 PM, Chen Gang <xili_gchen_5257@...mail.com> wrote:
> On 4/23/15 10:51, Steven Miao wrote:
>> On Wed, Apr 22, 2015 at 10:32 PM, Chen Gang <xili_gchen_5257@...mail.com> wrote:
>>> On 4/22/15 17:00, Steven Miao wrote:
>>>> Hi,
>>>>
>>>> On Thu, Apr 9, 2015 at 5:03 AM, Chen Gang <xili_gchen_5257@...mail.com> wrote:
>>>>> l1_text is at L1_CODE_START (e.g. for bf533, 0xff800000). If the kernel
>>>>> is too big, it may be overwritten, the related issue:
>>>>>
>>>>>     LD      init/built-in.o
>>>>>   init/built-in.o: In function `do_early_param':
>>>>>   init/main.c:(.init.text+0xe0): relocation truncated to fit: R_BFIN_PCREL24 against symbol `strcmp' defined in .l1.text section in arch/blackfin/lib/lib.a(strcmp.o)
>>>>>   init/main.c:(.init.text+0x10e): relocation truncated to fit: R_BFIN_PCREL24 against symbol `strcmp' defined in .l1.text section in arch/blackfin/lib/lib.a(strcmp.o)
>>>> blackfin toolchain generate 24 bit pc-relative calls by default, with
>>>> a range of –16,777,216 through 16,777,214 (0xFF00 0000 to 0x00FF FFFE)
>>>> is available.
>>>> So call to l1_text should be ok. What do you mean the kernel is too big?
>>>> http://docs.blackfin.uclinux.org/doku.php?id=ism:call
>>>>
>>>>
>>>
>>> Excuse me, I am not quite familiar with what you said above, can we
>>> also treat 24-bit as 16MB size limitation for kernel size? I am not
>>> quite sure, could you provide more information about it?.
>>>
>>> And I checked "arch/blackfin/kernel/vmlinux.lds.S", for me, in current
>>> case:
>> The memory address on blackfin usually starts from 0, if pc = 0, the
>> pc relative call range is [0xFF00 0000 - 0xFFFFFFFF, 0 -  0x00FF
>> FFFE], it covers L1 space.
>> If the kernel is big than 16M, eg. pc = 0x100 0000, the pc relative
>> call range accordingly is [0x1 - 0x100 0000, 0x100 0000 - 0x 1FF FFFE
>> ], it cann't call to L1 space.
>
> OK, thanks. I guess your meaning is:
>
>  - If the kernel is too big, it may let the pc which wants to call L1
>    space fail.
>
>  - So the kernel is too big to cause this issue, but it is nothing with
>    'overwritten' in my original patch comments.
>
Yes, it is.
>  - We can treat it as environments limitation, then can use COMPILE_TEST
>    for it. So this patch is still OK, except the related comments need
>    be improved (at least need to remove 'overwritten').
>
If pc-relative CALL will fail, there will be "relocation truncated to
fit: R_BFIN_PCREL24" warnings.
>>>
>>>  - init section is the last section of kernel, l1.text is within init
>>>    section, and it is in the fixed address. The other contents before
>>>    l1.text are dynamic (depend on kernel size).
>>>
>
> I guess, what I said above is meaningless (although it is correct).
>
>>>  - if kernel is too big, the contents before l1.text (the other contents
>>>    in .init.text) will override it, so ld reports issues.
>
Actually the kernel which is large the 16M could not happen, large
size kernel image is not sugguested on a embedded system.

> I guess, what I said above is incorrect.
>
>
> Are all of I guesses correct?
>
>
> Thanks.
> --
> Chen Gang
>
> Open, share, and attitude like air, water, and life which God blessed

-steven
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