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

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Date:	Fri, 10 Jun 2016 11:54:03 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Jason Baron <jbaron@...mai.com>
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 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