+CPPUNDEFS=
+dnl Check for silly hacked compilers predefining _FORTIFY_SOURCE.
+dnl Since we are building the implementations of the fortified functions here,
+dnl having the macro defined interacts very badly.
+AC_CACHE_CHECK([for _FORTIFY_SOURCE predefine], libc_cv_predef_fortify_source,
+[AC_TRY_COMPILE([], [
+#ifdef _FORTIFY_SOURCE
+# error bogon
+#endif],
+ [libc_cv_predef_fortify_source=no],
+ [libc_cv_predef_fortify_source=yes])])
+if test $libc_cv_predef_fortify_source = yes; then
+ CPPUNDEFS="${CPPUNDEFS:+$CPPUNDEFS }-U_FORTIFY_SOURCE"
+fi
+AC_SUBST(CPPUNDEFS)
+
+dnl Check for silly hacked compilers inserting -fstack-protector.
+dnl This breaks badly for the early startup code we compile, since
+dnl the compiled code can refer to a magic machine-dependent location
+dnl for the canary value before we have sufficient setup for that to
+dnl work. It's also questionable to build all of libc with this flag
+dnl even when you're doing that for most applications you build, since
+dnl libc's code is so heavily-used and performance-sensitive. If we
+dnl ever really want to make that work, it should be enabled explicitly
+dnl in the libc build, not inherited from implicit compiler settings.
+AC_CACHE_CHECK([whether $CC implicitly enables -fstack-protector],
+ libc_cv_predef_stack_protector, [
+AC_TRY_COMPILE([extern void foobar (char *);],
+ [char large_array[2048]; foobar (large_array);], [
+libc_undefs=`$NM -u conftest.o |
+ LC_ALL=C $AWK '$1 == "U" { print $2 | "sort -u"; next } { exit(1) }' \
+ 2>&AS_MESSAGE_LOG_FD` || {
+ AC_MSG_ERROR([confusing output from $NM -u])
+}
+echo >&AS_MESSAGE_LOG_FD "libc_undefs='$libc_undefs'"
+# On some architectures, there are architecture-specific undefined
+# symbols (resolved by the linker), so filter out unknown symbols.
+# This will fail to produce the correct result if the compiler
+# defaults to -fstack-protector but this produces an undefined symbol
+# other than __stack_chk_fail. However, compilers like that have not
+# been encountered in practice.
+libc_undefs=`echo "$libc_undefs" | egrep '^(foobar|__stack_chk_fail)$'`
+case "$libc_undefs" in
+foobar) libc_cv_predef_stack_protector=no ;;
+'__stack_chk_fail
+foobar') libc_cv_predef_stack_protector=yes ;;
+*) AC_MSG_ERROR([unexpected symbols in test: $libc_undefs]) ;;
+esac],
+ [AC_MSG_ERROR([test compilation failed])])
+])
+libc_extra_cflags=
+if test $libc_cv_predef_stack_protector = yes; then
+ libc_extra_cflags=-fno-stack-protector
+fi
+AC_SUBST(libc_extra_cflags)
+