linux-kernel - Re: [PATCH] arch: metag: lib: add "umoddi3.S" file for _

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Message-ID: <52B2F8DC.8060006@imgtec.com>
Date:	Thu, 19 Dec 2013 13:47:08 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Chen Gang <gang.chen.5i5j@...il.com>
CC:	<rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	<linux-metag@...r.kernel.org>
Subject: Re: [PATCH] arch: metag: lib: add "umoddi3.S" file for __umoddi3()

On 19/12/13 13:37, Chen Gang wrote:
> On 12/19/2013 08:17 PM, James Hogan wrote:
>> On 19/12/13 12:05, Chen Gang wrote:
>>> Use objdump to get "umoddi3.S" for __umoddi3(), the original binary
>>> file is "gcc-4.2.4-final/gcc/libgcc/umoddi3.o" which is generated by
>>> "gcc-4.2.4/gcc/libgcc2.c".
>>>
>>> The relate error with allmodconfig:
>>>
>>>     MODPOST 2909 modules
>>>   ERROR: "__umoddi3" [drivers/target/target_core_mod.ko] undefined!
>>
>> _umoddi3 is a 64bit division, which should be using the proper division
>> functions provided by the kernel in <linux/math64.h>.
>>
>> It needs fixing wherever it comes from in drivers/target/target_core_mod.ko.
>>
> 
> After disassemble target_core_mod.ko, for me, the compiler will use
> ___umoddi3 for '%' operator and use ___udivsi3 for '/' operator.

Yeh, % is in this case remainder from a 64bit division, for which the
standard division functions in <linux/math64.h> should be used instead.

> If what I guess is correct, we need use/copy the "system library" which
> compiler provides, so just use its ".o" file is OK (just like another
> "arch/metag/lib/*.S" have done).

No, I believe there shouldn't be any use of the C 64bit division/modulo
operations in generic kernel code in the first place, so like I said
before the code in question should be fixed to use the proper functions
in <linux/math64.h>.

Cheers
James

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