additional compiler hardening flags

[Corinna Vinschen]

Hi Darren,

On Apr 18 11:41, Darren Tucker wrote:
> On Thu, Apr 18, 2013 at 11:16:13AM +1000, Darren Tucker wrote:
> > Anyway, we could easily add a configure knob to turn it off should that
> > be necessary.
> 
> here's an updated patch without -fPIC, and with a configure knob
> (--without-hardening) to turn this off.
> [...]
> +dnl OSSH_CHECK_CFLAG_LINK(check_flag[, define_flag])
> +dnl Check that $LD accepts a flag 'check_flag'. If it is supported append
> +dnl 'define_flag' to $LDFLAGS. If 'define_flag' is not specified, then append
> +dnl 'check_flag'.
> +AC_DEFUN([OSSH_CHECK_LDFLAG_LINK], [{
> +	AC_MSG_CHECKING([if $LD supports $1])
> +	saved_LDFLAGS="$LDFLAGS"
> +	LDFLAGS="$LDFLAGS $1"
> +	_define_flag="$2"
> +	test "x$_define_flag" = "x" && _define_flag="$1"
> +	AC_LINK_IFELSE([AC_LANG_SOURCE([[int main(void) { return 0; }]])],
> +		[ AC_MSG_RESULT([yes])
> +		  LDFLAGS="$saved_LDFLAGS $_define_flag"],
> +		[ AC_MSG_RESULT([no])
> +		  LDFLAGS="$saved_LDFLAGS" ]
> +	)
> +}])

Does this check also catch the situation that commandline options
are only warned about?  On PE/COFF platforms, the -fPIE option is
ignored, but the build will then be littered with warnings:

   $ gcc -fPIE -c x.c
   x.c:1:0: warning: -fPIC ignored for target (all code is position independent) [enabled by default]
    #include <stdio.h>
    ^


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat