linux-kernel - Re: [PATCH 2/3] x86-64: use relative 32-bit pointers in exception tables

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Message-ID: <4D5DFA41.9060207@zytor.com>
Date:	Thu, 17 Feb 2011 20:49:05 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jan Beulich <JBeulich@...ell.com>
CC:	mingo@...e.hu, tglx@...utronix.de, tony.luck@...el.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] x86-64: use relative 32-bit pointers in exception
  tables

On 02/17/2011 09:03 AM, Jan Beulich wrote:
> Convert exception table pointers from absolute 64-bit to relative 32-
> bit ones, thus shrinking the table size by half. Rather than providing
> an x86-64-specific extable implementation, generalize the common one
> to deal with different ways of storing the pointers, which will allow
> ia64's custom implementation to be dropped subsequently.
> 
> Signed-off-by: Jan Beulich <jbeulich@...ell.com>
> Cc: Tony Luck <tony.luck@...el.com>
> --- /dev/null
> +++ 2.6.38-rc5-extable/include/asm-generic/extable.h
> @@ -0,0 +1,49 @@
> +#ifndef __ASM_GENERIC_EXTABLE_H
> +#define __ASM_GENERIC_EXTABLE_H
> +
> +/*
> + * The exception table consists of pairs of addresses: the first is the
> + * address of an instruction that is allowed to fault, and the second is
> + * the address at which the program should continue.  No registers are
> + * modified, so it is entirely up to the continuation code to figure out
> + * what to do.
> + *
> + * All the routines below use bits of fixup code that are out of line
> + * with the main instruction path.  This means when everything is well,
> + * we don't even have to jump over them.  Further, they do not intrude
> + * on our cache or tlb entries.
> + */
> +
> +struct exception_table_entry
> +{
> +#ifdef CONFIG_EXTABLE_RELATIVE_POINTERS
> +	s32 insn_off, fixup_off;
> +#else
> +	unsigned long insn, fixup;
> +#endif
> +};
> +

This breaks arch/x86/kernel/test_nx.c:

/home/hpa/kernel/linux-2.6-tip.asm/arch/x86/kernel/test_nx.c: In
function ‘fudze_exception_table’:
/home/hpa/kernel/linux-2.6-tip.asm/arch/x86/kernel/test_nx.c:62: error:
‘struct exception_table_entry’ has no member named ‘insn’
make[4]: *** [arch/x86/kernel/test_nx.o] Error 1
make[3]: *** [arch/x86/kernel] Error 2
make[2]: *** [arch/x86] Error 2
make[2]: *** Waiting for unfinished jobs....
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