Silence -Wattribute-warning in zfs_log_xvattr()

Silence the warnings about writing beyond the end of a the field.
In this instance the behavior is done intentionally and restructuring
the function would be disruptive for relatively little gain.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

config/always-compiler-options.m4

@@ -227,6 +227,29 @@ AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_CC_INFINITE_RECURSION], [
 	AC_SUBST([INFINITE_RECURSION])
 ])
 
+dnl #
+dnl # Check if cc supports -Wattribute-warning.
+dnl #
+AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_CC_ATTRIBUTE_WARNING], [
+	AC_MSG_CHECKING([whether $CC supports -Wattribute-warning])
+
+	saved_flags="$CFLAGS"
+	CFLAGS="$CFLAGS -Werror -Wattribute-warning"
+
+	AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [])], [
+		ATTRIBUTE_WARNING=-Wattribute-warning
+		AC_DEFINE([HAVE_ATTRIBUTE_WARNING], 1,
+			[Define if compiler supports -Wattribute-warning])
+		AC_MSG_RESULT([yes])
+	], [
+		ATTRIBUTE_WARNING=
+		AC_MSG_RESULT([no])
+	])
+
+	CFLAGS="$saved_flags"
+	AC_SUBST([ATTRIBUTE_WARNING])
+])
+
 dnl #
 dnl # Check if cc supports -fno-omit-frame-pointer option.
 dnl #

config/zfs-build.m4

@@ -210,6 +210,7 @@ AC_DEFUN([ZFS_AC_CONFIG_ALWAYS], [
 	AC_SUBST(CPU_COUNT)
 
 	ZFS_AC_CONFIG_ALWAYS_CC_NO_CLOBBERED
+	ZFS_AC_CONFIG_ALWAYS_CC_ATTRIBUTE_WARNING
 	ZFS_AC_CONFIG_ALWAYS_CC_INFINITE_RECURSION
 	ZFS_AC_CONFIG_ALWAYS_CC_IMPLICIT_FALLTHROUGH
 	ZFS_AC_CONFIG_ALWAYS_CC_FRAME_LARGER_THAN

module/zfs/zfs_log.c

@@ -104,6 +104,10 @@ zfs_log_create_txtype(zil_create_t type, vsecattr_t *vsecp, vattr_t *vap)
  * records a single 64 bit integer which has the bits to set on
  * replay for the xvattr.
  */
+#if defined(HAVE_ATTRIBUTE_WARNING)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wattribute-warning"
+#endif
 static void
 zfs_log_xvattr(lr_attr_t *lrattr, xvattr_t *xvap)
 {
@@ -189,6 +193,9 @@ zfs_log_xvattr(lr_attr_t *lrattr, xvattr_t *xvap)
 		*attrs |= (xoap->xoa_projinherit == 0) ? 0 :
 		    XAT0_PROJINHERIT;
 }
+#if defined(HAVE_ATTRIBUTE_WARNING)
+#pragma GCC diagnostic pop
+#endif
 
 static void *
 zfs_log_fuid_ids(zfs_fuid_info_t *fuidp, void *start)