linux-kernel - Re: [PATCH v2 4/4] dynamic_debug: add jump label support

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Message-ID: <575ADDB3.7070304@akamai.com>
Date:	Fri, 10 Jun 2016 11:33:07 -0400
From:	Jason Baron <jbaron@...mai.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<akpm@...ux-foundation.org>, <joe@...ches.com>,
	<peterz@...radead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] dynamic_debug: add jump label support



On 06/10/2016 05:54 AM, Arnd Bergmann wrote:
> On Friday, May 20, 2016 5:16:36 PM CEST Jason Baron wrote:
>> Although dynamic debug is often only used for debug builds, sometimes its
>> enabled for production builds as well. Minimize its impact by using jump
>> labels. This reduces the text section by 7000+ bytes in the kernel image
>> below. It does increase data, but this should only be referenced when
>> changing the direction of the branches, and hence usually not in cache.
>>
>>    text	   data	    bss	    dec	    hex	filename
>> 8194852	4879776	 925696	14000324	 d5a0c4	vmlinux.pre
>> 8187337	4960224	 925696	14073257	 d6bda9	vmlinux.post
>>
>> Signed-off-by: Jason Baron <jbaron@...mai.com>
>> ---
> 
> This causes problems for some of my randconfig builds, when a dynamic
> debug call is used inside of an __exit function:
> 
> `.exit.text' referenced in section `__jump_table' of drivers/built-in.o: defined in discarded section `.exit.text' of drivers/built-in.o
> `.exit.text' referenced in section `__jump_table' of drivers/built-in.o: defined in discarded section `.exit.text' of drivers/built-in.o
> 
> 	Arnd
> 

Hi,

I stuck pr_debug() in a few functions marked with __exit, but did not
reproduce yet. Can you share your .config and gcc --version.

Thanks,

-Jason