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

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Date:	Wed, 23 Nov 2011 17:53:21 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Rabin Vincent <rabin@....in>
Cc:	Jason Baron <jbaron@...hat.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] ARM: add jump label support

On Wed, Nov 23, 2011 at 08:25:09PM +0530, Rabin Vincent wrote:
> Here's a patch.  Atleast on MIPS %c means something else so I had to
> ifdef it for ARM:
> 
> 8<----------------------------
> >From ea211ce77e0ea9c5b8cd32b99bfb24e0140f0068 Mon Sep 17 00:00:00 2001
> From: Rabin Vincent <rabin@....in>
> Date: Wed, 23 Nov 2011 20:05:09 +0530
> Subject: [PATCH] jump label: detect %c support for ARM
> 
> Some versions of ARM GCC don't support the %c specifier fully, but do
> support asm goto.  Since we need the %c to support jump labels on ARM,
> detect that too in the asm goto detection script to avoid build errors
> with these versions.
> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48637
> 
> Signed-off-by: Rabin Vincent <rabin@....in>
> ---
>  scripts/gcc-goto.sh |   18 +++++++++++++++++-
>  1 files changed, 17 insertions(+), 1 deletions(-)
> 
> diff --git a/scripts/gcc-goto.sh b/scripts/gcc-goto.sh
> index 98cffcb..9b744de 100644
> --- a/scripts/gcc-goto.sh
> +++ b/scripts/gcc-goto.sh
> @@ -2,4 +2,20 @@
>  # Test for gcc 'asm goto' support
>  # Copyright (C) 2010, Jason Baron <jbaron@...hat.com>
>  
> -echo "int main(void) { entry: asm goto (\"\"::::entry); return 0; }" | $@ -x c - -c -o /dev/null >/dev/null 2>&1 && echo "y"
> +cat << "END" | $@ -x c - -c -o /dev/null >/dev/null 2>&1 && echo "y"
> +int main(void)
> +{
> +#ifdef __arm__
> +	/*
> +	 * Not related to asm goto, but used by jump label
> +	 * and broken on some ARM GCC versions (see GCC Bug 48637).
> +	 */
> +	static struct { int dummy; int state; } tp;
> +	asm ("@ %c0" :: "i" (&tp.state));
> +#endif
> +
> +entry:
> +	asm goto ("" :::: entry);
> +	return 0;
> +}
> +END

Is the presence of asm goto and %c something we want to test together or
separately?  I suspect it's something we want to do separately.
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