build: initialize stack variables to zero by default

Newer versions of gcc and clang can include the ability to zero stack
variables by default.  Let's enable it so that we (a) reduce the risk of
writing stack contents to disk somewhere and (b) try to reduce
unpredictable program behavior based on random stack contents.  The
kernel added this 6 years ago, so I think it's mature enough for
xfsprogs.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reluctantly-Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/configure.ac b/configure.ac
index 224d1d3930bf2f1fb01c83ddb584b30cc8342734..90ef7925a925d0d33b89c58083c26f35791c7317 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -177,6 +177,7 @@ AC_CONFIG_SYSTEMD_SYSTEM_UNIT_DIR
 AC_CONFIG_CROND_DIR
 AC_CONFIG_UDEV_RULE_DIR
 AC_HAVE_BLKID_TOPO
+AC_HAVE_TRIVIAL_AUTO_VAR_INIT
 
 if test "$enable_ubsan" = "yes" || test "$enable_ubsan" = "probe"; then
         AC_PACKAGE_CHECK_UBSAN

diff --git a/include/builddefs.in b/include/builddefs.in
index ac43b6412c8cbb43407186bda84d8be6d4e052b7..82840ec7fd3adbcc1f1fefc76ad2e3f02cb87e07 100644 (file)
--- a/include/builddefs.in
+++ b/include/builddefs.in
@@ -146,7 +146,7 @@ ifeq ($(HAVE_LIBURCU_ATOMIC64),yes)
 PCFLAGS += -DHAVE_LIBURCU_ATOMIC64
 endif
 
-SANITIZER_CFLAGS += @addrsan_cflags@ @threadsan_cflags@ @ubsan_cflags@
+SANITIZER_CFLAGS += @addrsan_cflags@ @threadsan_cflags@ @ubsan_cflags@ @autovar_init_cflags@
 SANITIZER_LDFLAGS += @addrsan_ldflags@ @threadsan_ldflags@ @ubsan_ldflags@
 
 # Use special ar/ranlib wrappers if we have lto

diff --git a/m4/package_sanitizer.m4 b/m4/package_sanitizer.m4
index 41b729906a27ba8fe797bf13cf70c5d51f130408..6488f7ebce2f50c4970ce5b109655fdaf7f2abe6 100644 (file)
--- a/m4/package_sanitizer.m4
+++ b/m4/package_sanitizer.m4
@@ -57,3 +57,17 @@ AC_DEFUN([AC_PACKAGE_CHECK_THREADSAN],
     AC_SUBST(threadsan_cflags)
     AC_SUBST(threadsan_ldflags)
   ])
+
+# Check if we have -ftrivial-auto-var-init=zero
+AC_DEFUN([AC_HAVE_TRIVIAL_AUTO_VAR_INIT],
+  [ AC_MSG_CHECKING([if C compiler supports zeroing automatic vars])
+    OLD_CFLAGS="$CFLAGS"
+    TEST_CFLAGS="-ftrivial-auto-var-init=zero"
+    CFLAGS="$CFLAGS $TEST_CFLAGS"
+    AC_LINK_IFELSE([AC_LANG_PROGRAM([])],
+        [AC_MSG_RESULT([yes])]
+        [autovar_init_cflags=$TEST_CFLAGS],
+        [AC_MSG_RESULT([no])])
+    CFLAGS="${OLD_CFLAGS}"
+    AC_SUBST(autovar_init_cflags)
+  ])