linux-kernel - Re: Linux kernel cross-compilers

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Date:	Fri, 16 Aug 2013 08:43:35 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Max Filippov <jcmvbkbc@...il.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Linux kernel cross-compilers

On 08/16/2013 02:45 AM, Max Filippov wrote:
>>> Guenter,
>>> can you share a complete build log with V=1?
>>>
>>
>> http://roeck-us.net/linux/logs/make.xtensa.log.bad
>> http://roeck-us.net/linux/logs/make.xtensa.log.ok
>>
>> Key difference: the failing command in the bad case is
>>          xtensa-linux-objcopy -O elf32-xtensa-le
>> and in the good case
>>          xtensa-linux-objcopy -O elf32-xtensa-be
>>
>> Same compiler (4.6.3 from kernel.org), same configuration file, same command
>> line.
>> Configuration file is generated from defconfig, and the resulting .config
>> file
>> is the same in both cases.
>>
>> If I execute make and expicitly set BIG_ENDIAN=1 on the failing system as
>> parameter to it,
>> it works fine. If I set BIG_ENDIAN=0 on the passing system, it fails.
>>
>> I am puzzled. Guess there must be something different, but I have no idea
>> what it might be.
>
> What is the output of
>
> echo -e __XTENSA_EB__ | xtensa-linux-gcc -E -
>
> on the failing system?
>
It is "1", but that let me pinpoint the problem.

On the failing system, the version of echo executed by make does
not understand the "-e" option. Thus, when running arch/xtensa/boot/Makefile,
"echo -e __XTENSA_EB__" returns "-e __XTENSA_EB__", which doesn't compile,
and BIG_ENDIAN ends up being 0. So the compiler is completely innocent.

I found out the root source: SHELL is set the /bin/sh, which on the failing
system points to /bin/dash (default in Ubuntu, or at least it used to be).
dash apparently has a built-in version of echo which does not understand '-e'.
Oh well.

Thanks a lot for helping me to track this down!

Guenter

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