linux-kernel - [tip:x86/x32] x32: Fix alignment fail in struct compat

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Message-ID: <tip-31796ac4e8f0e88f5c10f1ad6dab8f19bebe44a4@git.kernel.org>
Date:	Wed, 14 Mar 2012 14:43:36 -0700
From:	"tip-bot for H. Peter Anvin" <hpa@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	tglx@...utronix.de, hjl.tools@...il.com
Subject: [tip:x86/x32] x32: Fix alignment fail in struct compat_siginfo

Commit-ID:  31796ac4e8f0e88f5c10f1ad6dab8f19bebe44a4
Gitweb:     http://git.kernel.org/tip/31796ac4e8f0e88f5c10f1ad6dab8f19bebe44a4
Author:     H. Peter Anvin <hpa@...or.com>
AuthorDate: Wed, 14 Mar 2012 14:27:52 -0700
Committer:  H. Peter Anvin <hpa@...or.com>
CommitDate: Wed, 14 Mar 2012 14:27:52 -0700

x32: Fix alignment fail in struct compat_siginfo

Adding struct _sigchld_x32 caused a misalignment cascade in struct
siginfo, because union _sifields is located on an 4-byte boundary
(8-byte misaligned.)

Adding new fields that are 8-byte aligned caused the intermediate
structures to also be aligned to 8 bytes, thereby adding padding in
unexpected places.

Thus, change s64 to compat_s64 here, which makes it "misaligned on
paper".  In reality these fields *are* actually aligned (there are 3
preceeding ints outside the union and 3 inside struct _sigchld_x32),
but because of the intervening union and struct it is not possible for
gcc to avoid padding without breaking the ABI.

Reported-and-tested-by: H. J. Lu <hjl.tools@...il.com>
Signed-off-by: H. Peter Anvin <hpa@...or.com>
Link: http://lkml.kernel.org/r/1329696488-16970-1-git-send-email-hpa@zytor.com
---
 arch/x86/include/asm/ia32.h |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/ia32.h b/arch/x86/include/asm/ia32.h
index 7d0c185..ee52760 100644
--- a/arch/x86/include/asm/ia32.h
+++ b/arch/x86/include/asm/ia32.h
@@ -130,8 +130,8 @@ typedef struct compat_siginfo {
 			unsigned int _pid;	/* which child */
 			unsigned int _uid;	/* sender's uid */
 			int _status;		/* exit code */
-			s64 _utime;
-			s64 _stime;
+			compat_s64 _utime;
+			compat_s64 _stime;
 		} _sigchld_x32;
 
 		/* SIGILL, SIGFPE, SIGSEGV, SIGBUS */
--
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