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* [patch] s390 kprobes: Align probe address
@ 2007-03-22  1:09 David Wilder
  0 siblings, 0 replies; only message in thread
From: David Wilder @ 2007-03-22  1:09 UTC (permalink / raw)
  To: linux-kernel, akpm, schwidefsky

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[This patch applies to both linux and mm trees.  Please send comments 
off list, thanks]

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Running a probe on s390 with a probe address that is not 4 byte aligned
results in a Kernel BUG.  The problem is that the stura instruction used
by swap_instruction requires the destination address to be 4 byte aligned.
As stura only writes 4 bytes, aligning to the next 4 byte aligned address
results in the breakpoint instruction being stored past the probe address.
The fix is to align the address backward (to the previous 4 byte aligned
address) and writing the two byte breakpoint instruction in the appropriate

Signed-off-by: David Wilder <>
diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
index 8af549e..993f353 100644
--- a/arch/s390/kernel/kprobes.c
+++ b/arch/s390/kernel/kprobes.c
@@ -167,7 +167,7 @@ static int __kprobes swap_instruction(vo
 	 * shall not cross any page boundaries (vmalloc area!) when writing
 	 * the new instruction.
-	addr = (u32 *)ALIGN((unsigned long)args->ptr, 4);
+	addr = (u32 *)((unsigned long)args->ptr & -4UL);
 	if ((unsigned long)args->ptr & 2)
 		instr = ((*addr) & 0xffff0000) | args->new;

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2007-03-22  1:09 [patch] s390 kprobes: Align probe address David Wilder

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