From b83e3e48c9b183a80dd00eb6c7431a1cbc7d89c9 Mon Sep 17 00:00:00 2001
From: Richard Yao <ryao@gentoo.org>
Date: Tue, 10 Sep 2013 15:13:44 -0400
Subject: [PATCH] Stop runtime pointer modifications in autotools checks

c38367c73f592ca9729ba0d5e70b5e3bc67e0745 was meant to eliminate runtime
function pointer modifications in autotools checks because they were
prone to false negatives on kernels hardened by the PaX project.
Unfortunately, I missed the xattr_handler and super_block->s_bdi
autotools checks. Recent changes to PaX constified
xattr_handler->get/set, which lead me to discover this oversight.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1433
---
 config/kernel-bdi.m4           |  7 +++++--
 config/kernel-xattr-handler.m4 | 33 +++++++++++++++++++--------------
 2 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/config/kernel-bdi.m4 b/config/kernel-bdi.m4
index 34ffaabd5b..aec7b73478 100644
--- a/config/kernel-bdi.m4
+++ b/config/kernel-bdi.m4
@@ -6,9 +6,12 @@ AC_DEFUN([ZFS_AC_KERNEL_BDI], [
 	AC_MSG_CHECKING([whether super_block has s_bdi])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/fs.h>
+
+		static const struct super_block
+		    sb __attribute__ ((unused)) {
+			.s_bdi = NULL,
+		}
 	],[
-		struct super_block sb __attribute__ ((unused));
-		sb.s_bdi = NULL;
 	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_BDI, 1, [struct super_block has s_bdi])
diff --git a/config/kernel-xattr-handler.m4 b/config/kernel-xattr-handler.m4
index 325c960df6..943f9033c3 100644
--- a/config/kernel-xattr-handler.m4
+++ b/config/kernel-xattr-handler.m4
@@ -18,10 +18,11 @@ AC_DEFUN([ZFS_AC_KERNEL_CONST_XATTR_HANDLER],
 		const struct xattr_handler *xattr_handlers[] = {
 			&xattr_test_handler,
 		};
-	],[
-		struct super_block sb __attribute__ ((unused));
 
-		sb.s_xattr = xattr_handlers;
+		const struct super_block sb __attribute__ ((unused)) = {
+			.s_xattr = xattr_handlers,
+		};
+	],[
 	],[
 		AC_MSG_RESULT([yes])
 		AC_DEFINE(HAVE_CONST_XATTR_HANDLER, 1,
@@ -40,12 +41,14 @@ AC_DEFUN([ZFS_AC_KERNEL_XATTR_HANDLER_GET], [
 	AC_MSG_CHECKING([whether xattr_handler->get() wants dentry])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/xattr.h>
-	],[
-		int (*get)(struct dentry *dentry, const char *name,
-		    void *buffer, size_t size, int handler_flags) = NULL;
-		struct xattr_handler xops __attribute__ ((unused));
 
-		xops.get = get;
+		int get(struct dentry *dentry, const char *name,
+		    void *buffer, size_t size, int handler_flags) { return 0; }
+		static const struct xattr_handler
+		    xops __attribute__ ((unused)) = {
+			.get = get,
+		};
+	],[
 	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_DENTRY_XATTR_GET, 1,
@@ -64,13 +67,15 @@ AC_DEFUN([ZFS_AC_KERNEL_XATTR_HANDLER_SET], [
 	AC_MSG_CHECKING([whether xattr_handler->set() wants dentry])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/xattr.h>
-	],[
-		int (*set)(struct dentry *dentry, const char *name,
-		    const void *buffer, size_t size, int flags,
-		    int handler_flags) = NULL;
-		struct xattr_handler xops __attribute__ ((unused));
 
-		xops.set = set;
+		int set(struct dentry *dentry, const char *name,
+		    const void *buffer, size_t size, int flags,
+		    int handler_flags) { return 0; }
+		static const struct xattr_handler
+		    xops __attribute__ ((unused)) = {
+			.set = set,
+		};
+	],[
 	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_DENTRY_XATTR_SET, 1,