upstream

[gnu-emacs] / configure.ac

diff --git a/configure.ac b/configure.ac
index 9656319ef63237434db4e133d7af9edea6e3c6f2..357474e0bbe54ef18a7ae2f47ecb981b276f0ced 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -712,6 +712,8 @@ else
   nw="$nw -Wfloat-equal"            # warns about high-quality code
   nw="$nw -Winline"                 # OK to ignore 'inline'
   nw="$nw -Wjump-misses-init"       # We sometimes safely jump over init.
+  nw="$nw -Wstrict-overflow"        # OK to optimize assuming that
+                                    # signed overflow has undefined behavior
   nw="$nw -Wsync-nand"              # irrelevant here, and provokes ObjC warning
   nw="$nw -Wunsafe-loop-optimizations" # OK to suppress unsafe optimizations
 
@@ -719,11 +721,23 @@ else
   # <http://lists.gnu.org/archive/html/emacs-diffs/2011-11/msg00265.html>.
   nw="$nw -Wshadow"
 
-  # The following lines should be removable at some point.
-  nw="$nw -Wstack-protector"
-  nw="$nw -Wstrict-overflow"
+  # The following line should be removable at some point.
   nw="$nw -Wsuggest-attribute=pure"
 
+  AC_MSG_CHECKING([whether to use -Wstack-protector])
+  AC_PREPROC_IFELSE(
+    [AC_LANG_PROGRAM(
+       [[#if (1 <= __LONG_MAX__ >> 31 >> 31 \
+           && 4 < __GNUC__ + (7 < __GNUC_MINOR__ + (2 <= __GNUC_PATCHLEVEL__)))
+          /* OK */
+         #else
+          #error "Not GCC, or GCC before 4.7.2, or 'long int' has < 64 bits."
+        #endif
+       ]])],
+    [AC_MSG_RESULT(yes)],
+    [AC_MSG_RESULT(no)
+     nw="$nw -Wstack-protector"])
+
   gl_MANYWARN_ALL_GCC([ws])
   gl_MANYWARN_COMPLEMENT([ws], [$ws], [$nw])
   for w in $ws; do