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AC_DEFUN([CHECK_CFLAG], [
AC_LANG_ASSERT(C)
AC_MSG_CHECKING([if $saved_CC supports "$1"])
old_cflags="$CFLAGS"
CFLAGS="$1 -Wall -Werror"
AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <stdio.h>]], [[printf("Hello")]])],
[AC_MSG_RESULT([yes])
CFLAGS=$old_cflags
HARDEN_CFLAGS="$HARDEN_CFLAGS $1"],
[AC_MSG_RESULT([no])
CFLAGS=$old_cflags
[$2]])
])
AC_DEFUN([CHECK_LDFLAG], [
AC_LANG_ASSERT(C)
AC_MSG_CHECKING([if $saved_LD supports "$1"])
old_ldflags="$LDFLAGS"
LDFLAGS="$1 -Wall -Werror"
AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <stdio.h>]], [[printf("Hello")]])],
[AC_MSG_RESULT([yes])
LDFLAGS=$old_ldflags
HARDEN_LDFLAGS="$HARDEN_LDFLAGS $1"],
[AC_MSG_RESULT([no])
LDFLAGS=$old_ldflags
[$2]])
])
AC_DEFUN([DISABLE_AS_EXECUTABLE_STACK], [
save_cflags="$CFLAGS"
CFLAGS=
AC_MSG_CHECKING([whether AS supports .note.GNU-stack])
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
__asm__(".section .note.GNU-stack,\"\",@progbits");]])],
[AC_MSG_RESULT([yes])]
[AM_CFLAGS=-DHAVE_GNU_STACK],
[AC_MSG_RESULT([no])]
)
CFLAGS="$save_cflags $AM_CFLAGS"
])
AC_DEFUN([CHECK_C_HARDENING_OPTIONS], [
AC_ARG_ENABLE([hardening],
[AS_HELP_STRING([--disable-hardening],
[Disable options to frustrate memory corruption exploits])],
[], [enable_hardening=yes])
AC_ARG_ENABLE([windows-ssp],
[AS_HELP_STRING([--enable-windows-ssp],
[Enable building the stack smashing protection on
Windows. This currently distributing libssp-0.dll.])])
# We want to check for compiler flag support. Prior to clang v5.1, there was no
# way to make clang's "argument unused" warning fatal. So we invoke the
# compiler through a wrapper script that greps for this message.
saved_CC="$CC"
saved_LD="$LD"
flag_wrap="$srcdir/scripts/wrap-compiler-for-flag-check"
CC="$flag_wrap $CC"
LD="$flag_wrap $LD"
AS_IF([test "x$enable_hardening" = "xyes"], [
# Tell GCC to NOT optimize based on signed arithmetic overflow
CHECK_CFLAG([[-fno-strict-overflow]])
# _FORTIFY_SOURCE replaces builtin functions with safer versions.
AS_IF([test "x$HOST_OS" != "xwin"], [
AX_ADD_FORTIFY_SOURCE
])
# Enable read only relocations
CHECK_LDFLAG([[-Wl,-z,relro]])
CHECK_LDFLAG([[-Wl,-z,now]])
# Windows security flags
AS_IF([test "x$HOST_OS" = "xwin"], [
CHECK_LDFLAG([[-Wl,--nxcompat]])
CHECK_LDFLAG([[-Wl,--dynamicbase]])
CHECK_LDFLAG([[-Wl,--high-entropy-va]])
])
# Use stack-protector-strong if available; if not, fallback to
# stack-protector-all which is considered to be overkill
AS_IF([test "x$enable_windows_ssp" = "xyes" -o "x$HOST_OS" != "xwin"], [
CHECK_CFLAG([[-fstack-protector-strong]],
CHECK_CFLAG([[-fstack-protector-all]],
AC_MSG_WARN([compiler does not appear to support stack protection])
)
)
AS_IF([test "x$HOST_OS" = "xwin"], [
AC_SEARCH_LIBS([__stack_chk_guard],[ssp])
])
])
])
# Restore CC, LD
CC="$saved_CC"
LD="$saved_LD"
CFLAGS="$CFLAGS $HARDEN_CFLAGS"
LDFLAGS="$LDFLAGS $HARDEN_LDFLAGS"
])
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