linux-kernel - Re: [PATCH] kallsyms: ignore ARM mode switching veneers

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Date:	Fri, 26 Feb 2016 21:21:22 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Ard Biesheuvel <ard.biesheuvel@...aro.org>, mmarek@...e.cz,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kallsyms: ignore ARM mode switching veneers

On Friday 26 February 2016 20:50:54 Ard Biesheuvel wrote:
> On ARM, the linker may emit veneers to deal with relative branch
> instructions that appear too far away from their targets. Since the second
> kallsyms pass results in an increase of the kernel size, it may result in
> additional veneers to be emitted, potentially affecting the output of
> kallsyms itself if these symbols are visible to it, and for that reason,
> symbols whose names end in '_veneer' are ignored explicitly.
> 
> However, when building Thumb2 kernels, such veneers are named differently
> if they also incur a mode switch, and since they are not filtered by
> kallsyms, they may cause the build to fail. So filter symbols whose names
> end in '_from_arm' or '_from_thumb' as well.
> 
> Cc: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>


Thanks again for debugging this!

I have two (randconfig) configurations that ran into this problem, and they
are both with your patch

Tested-by: Arnd Bergmann <arnd@...db.de>

>  scripts/kallsyms.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index 8fa81e84e295..e2379de76563 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -215,6 +215,8 @@ static int symbol_valid(struct sym_entry *s)
>  
>  	static char *special_suffixes[] = {
>  		"_veneer",		/* arm */
> +		"_from_arm",		/* arm */
> +		"_from_thumb",		/* arm */
>  		NULL };
>  
>  	int i;
>