linux-kernel - Re: dynamic ftrace/recordmcount.c problem on ARMv5

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Date:	Wed, 13 Jan 2016 17:23:52 +0100
From:	Marc Kleine-Budde <mkl@...gutronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, ptx kernel <kernel@...gutronix.de>
Subject: Re: dynamic ftrace/recordmcount.c problem on ARMv5

On 01/13/2016 05:08 PM, Steven Rostedt wrote:
> On Wed, 13 Jan 2016 09:51:28 +0100
> Marc Kleine-Budde <mkl@...gutronix.de> wrote:
> 
>> There are 5 calls to __gnu_mcount_nc in the object file:
>>> $ objdump -x arch/arm/kernel/stacktrace.o | grep R_ARM_CALL | grep __gnu_mcount_nc
>>> 00000054 R_ARM_CALL        __gnu_mcount_nc
>>> 0000016c R_ARM_CALL        __gnu_mcount_nc
>>> 00000234 R_ARM_CALL        __gnu_mcount_nc
>>> 0000026c R_ARM_CALL        __gnu_mcount_nc
>>> 000002f4 R_ARM_CALL        __gnu_mcount_nc  
>>
>> However there are 6 references in the __mcount_loc section:
>>> $ readelf -R __mcount_loc arch/arm/kernel/stacktrace.o                            
>>>
>>> Hex dump of section '__mcount_loc':
>>>   0x00000000 24000000 54000000 6c010000 34020000 $...T...l...4...
>>>   0x00000010 6c020000 f4020000                   l.......  
>>
>> Note: The first and wrong offset is 0x24, which is a "bx r6" (see above
>> objdump of stacktrace.o):
>>>   24:	e12fff16 	bx	r6  
> 
> Interesting. Have you tried a make mrproper and tried again? Also, do
> you use hardlinks with ccache?

That happens on ARMv5 with a clean build. No ccache involved (this issue
should be fixed on >= v4.4)

>> I hacked scripts/Makefile.build to use the perl version of recordmcount,
>> that works without problems.
> 
> Note, you could also just removed CONFIG_HAVE_C_RECORDMCOUNT from
> arch/arm/Kconfig.

This is the patch I'm using as a workaround.

regards,
Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
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