linux-kernel - [PATCH] x86/alternatives: check replacementlen <= instrlen at build time

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Message-Id: <4B0FF8AA0200007800022703@vpn.id2.novell.com>
Date:	Fri, 27 Nov 2009 15:04:58 +0000
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	<mingo@...e.hu>, <tglx@...utronix.de>, <hpa@...or.com>
Cc:	<linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/alternatives: check replacementlen <= instrlen at
	 build time

Having run into the run-(boot-)time check a couple of times lately, I
finally took time to find a build-time check so that one doesn't need
to analyze the register/stack dump and resolve this (through manual
lookup in vmlinux) to the offending construct. The assembler will emit
a message like "Error: value of <num> too large for field of 1 bytes
at <offset>", which while not pointing out the source location still
makes analysis quite a bit easier.

Signed-off-by: Jan Beulich <jbeulich@...ell.com>

---
 arch/x86/include/asm/alternative.h     |    1 +
 1 files changed, 1 insertion(+)

--- linux-2.6.32-rc8/arch/x86/include/asm/alternative.h
+++ 2.6.32-rc8-x86-alternative/arch/x86/include/asm/alternative.h
@@ -84,6 +84,7 @@ static inline void alternatives_smp_swit
       "	 .byte " __stringify(feature) "\n"	/* feature bit     */	\
       "	 .byte 662b-661b\n"			/* sourcelen       */	\
       "	 .byte 664f-663f\n"			/* replacementlen  */	\
+      "	 .byte 0xff + (664f-663f) - (662b-661b)\n" /* rlen <= slen */	\
       ".previous\n"							\
       ".section .altinstr_replacement, \"ax\"\n"			\
       "663:\n\t" newinstr "\n664:\n"		/* replacement     */	\



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