[RFC][PATCH]fix search_extable() to find correct entry

[Masami Hiramatsu <hiramatu@sdl.hitachi.co.jp>]

Hi, Tony

I found a suspicious buggy code in the linux kernel on IA64 arch.
As far as I can see, search_extable() doesn't work correctly, because
the lookup routine expects that the address format of the
exception_table_entry is "IP + slot", but the compiler (gcc-3.4.5)
generates it as "IP + (slot << 2)". Thus the lookup routine always
fails to find the corresponding entry.
You can check it by dumping __ex_table section of vmlinux.

I made a patch to fix this bug attached in this mail. This patch is
against 2.6.17-rc6-mm2.
Please review it.

Description:
 Fix search_extable() and ia64_handle_exception() to handle the
address format of exception_table_entry correctly.

Thanks,

-- 
Masami HIRAMATSU
2nd Research Dept.
Hitachi, Ltd., Systems Development Laboratory
E-mail: hiramatu@sdl.hitachi.co.jp

Signed-off-by: Masami Hiramatsu <hiramatu@sdl.hitachi.co.jp>

 arch/ia64/mm/extable.c     |    7 ++++---
 include/asm-ia64/uaccess.h |    4 ++--
 2 files changed, 6 insertions(+), 5 deletions(-)
diff --exclude=CVS -Narup a/arch/ia64/mm/extable.c b/arch/ia64/mm/extable.c
--- a/arch/ia64/mm/extable.c	2005-10-28 09:02:08.000000000 +0900
+++ b/arch/ia64/mm/extable.c	2006-06-14 14:59:11.000000000 +0900
@@ -63,9 +63,10 @@ search_extable (const struct exception_t
 	unsigned long mid_ip;
 	long diff;

+	ip = (ip & ~0xf) + ((ip & 0x3) << 2);
         while (first <= last) {
 		mid = &first[(last - first)/2];
-		mid_ip = (u64) &mid->addr + mid->addr;
+		mid_ip = ((u64) &mid->addr + mid->addr) & ~0x3;
 		diff = mid_ip - ip;
                 if (diff = 0)
                         return mid;
@@ -83,8 +84,8 @@ ia64_handle_exception (struct pt_regs *r
 	long fix = (u64) &e->cont + e->cont;

 	regs->r8 = -EFAULT;
-	if (fix & 4)
+	if (fix & 2)
 		regs->r9 = 0;
 	regs->cr_iip = fix & ~0xf;
-	ia64_psr(regs)->ri = fix & 0x3;		/* set continuation slot number */
+	ia64_psr(regs)->ri = (fix & 0xc) >> 2;		/* set continuation slot number */
 }
diff --exclude=CVS -Narup a/include/asm-ia64/uaccess.h b/include/asm-ia64/uaccess.h
--- a/include/asm-ia64/uaccess.h	2005-10-28 09:02:08.000000000 +0900
+++ b/include/asm-ia64/uaccess.h	2006-06-14 23:54:55.000000000 +0900
@@ -139,7 +139,7 @@ do {												\
 	register long __gu_r8 asm ("r8") = 0;							\
 	register long __gu_r9 asm ("r9");							\
 	asm ("\n[1:]\tld"#n" %0=%2%P2\t// %0 and %1 get overwritten by exception handler\n"	\
-	     "\t.xdata4 \"__ex_table\", 1b-., 1f-.+4\n"						\
+	     "\t.xdata4 \"__ex_table\", 1b-., 1f-.+2\n"						\
 	     "[1:]"										\
 	     : "=r"(__gu_r9), "=r"(__gu_r8) : "m"(__m(addr)), "1"(__gu_r8));			\
 	(err) = __gu_r8;									\
@@ -346,7 +346,7 @@ extern unsigned long __strnlen_user (con

 struct exception_table_entry {
 	int addr;	/* location-relative address of insn this fixup is for */
-	int cont;	/* location-relative continuation addr.; if bit 2 is set, r9 is set to 0 */
+	int cont;	/* location-relative continuation addr.; if bit 1 is set, r9 is set to 0 */
 };

 extern void ia64_handle_exception (struct pt_regs *regs, const struct exception_table_entry *e);