# DP: Turn on -D_FORTIFY_SOURCE=2 by default for C, C++, ObjC, ObjC++,
# DP: if the optimization level is > 0

---
 gcc/doc/invoke.texi          |    6 ++++++
 gcc/c-family/c-cppbuiltin.c  |    3 +
 2 files changed, 9 insertions(+), 0 deletions(-)

Index: b/gcc/doc/invoke.texi
===================================================================
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -7840,6 +7840,12 @@ also turns on the following optimization
 Please note the warning under @option{-fgcse} about
 invoking @option{-O2} on programs that use computed gotos.
 
+NOTE: In Alpine Linux, @option{-D_FORTIFY_SOURCE=2} is
+set by default, and is activated when @option{-O} is set to 2 or higher.
+This enables additional compile-time and run-time checks for several libc
+functions.  To disable, specify either @option{-U_FORTIFY_SOURCE} or
+@option{-D_FORTIFY_SOURCE=0}.
+
 @item -O3
 @opindex O3
 Optimize yet more.  @option{-O3} turns on all optimizations specified
Index: b/gcc/c-family/c-cppbuiltin.c
===================================================================
--- a/gcc/c-family/c-cppbuiltin.c
+++ b/gcc/c-family/c-cppbuiltin.c
@@ -1176,6 +1176,10 @@ c_cpp_builtins (cpp_reader *pfile)
   builtin_define_with_value ("__REGISTER_PREFIX__", REGISTER_PREFIX, 0);
   builtin_define_with_value ("__USER_LABEL_PREFIX__", user_label_prefix, 0);
 
+  /* Fortify Source enabled by default for optimization levels > 0 */
+  if (optimize)
+    builtin_define_with_int_value ("_FORTIFY_SOURCE", 2);
+
   /* Misc.  */
   if (flag_gnu89_inline)
     cpp_define (pfile, "__GNUC_GNU_INLINE__");