linux-kernel - [PATCH] nios2: __kuser

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Date:	Thu, 22 Jan 2015 15:14:31 +0800
From:	Chung-Lin Tang <chunglin.tang@...il.com>
To:	linux-kernel@...r.kernel.org
CC:	Ley Foon Tan <lftan@...era.com>,
	Tobias Klauser <tklauser@...tanz.ch>, cltang@...esourcery.com
Subject: [PATCH] nios2: __kuser_sigtramp placement fix

The address of __kuser_sigtramp is wrong by one word, due to padding
__kuser_cmpxchg to fully 64 bytes. The version word at the start of the
page displaces __kuser_sigtramp to 0x1044, instead of the intended 0x1040.

Fixed by counting the 64-byte frame from the start of the page instead
of __kuser_cmpxchg. This shortens the __kuser_cmpxchg frame to 60-bytes,
but that's likely enough.

The zero-byte padding parts of the kuser_pad macro has been removed, due
to the .if command refusing to behave properly when there are other
.word directives in between. Probably a binutils gas bug.

Thanks,
Chung-Lin

Cc: Ley Foon Tan <lftan@...era.com>
Cc: Tobias Klauser <tklauser@...tanz.ch>
Signed-off-by: Chung-Lin Tang <cltang@...esourcery.com>

diff --git a/arch/nios2/kernel/entry.S b/arch/nios2/kernel/entry.S
index 0bdfd13..3224839 100644
--- a/arch/nios2/kernel/entry.S
+++ b/arch/nios2/kernel/entry.S
@@ -492,14 +492,7 @@ ENTRY(ret_from_kernel_thread)

  /* Filling pads with undefined instructions. */
 .macro	kuser_pad sym size
-	.if	((. - \sym) & 3)
-	.rept	(4 - (. - \sym) & 3)
-	.byte	0
-	.endr
-	.endif
-	.rept	((\size - (. - \sym)) / 4)
-	.word	0xdeadbeef
-	.endr
+	.fill	((\size - (. - \sym)) / 4), 4, 0xdeadbeef
 .endm

 	.align	6
@@ -526,7 +519,10 @@ cmpxchg_stw:
 cmpxchg_ret:
 	ret

-	kuser_pad __kuser_cmpxchg, 64
+	/* The first 64-byte frame contains the version word, so note
+	   that the first padding entry is based from the start of the kuser
+	   page, instead of __kuser_cmpxchg.  */
+	kuser_pad __kuser_helper_start, 64

 	.globl	__kuser_sigtramp
 __kuser_sigtramp:
--
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