Re: [Qemu-devel] [PATCH] configure: add option to disable -fstack-protector flags

[Stefan Weil <sw@weilnetz.de>]

Hi,

please see comments below.

Am 13.01.2014 21:00, schrieb Steven Noonan:
> The -fstack-protector flag family is useful for ensuring safety and for
> debugging, but has a performance impact. Here are some boot time comparisons of
> the various versions of -fstack-protector using qemu-system-arm on an x86_64
> host:
> 
>     # -fstack-protector-all
>     Startup finished in 1.810s (kernel) + 12.331s (initrd) + 49.016s (userspace) = 1min 3.159s
>     Startup finished in 1.801s (kernel) + 12.287s (initrd) + 47.925s (userspace) = 1min 2.013s
>     Startup finished in 1.812s (kernel) + 12.302s (initrd) + 47.995s (userspace) = 1min 2.111s
> 
>     # -fstack-protector-strong
>     Startup finished in 1.744s (kernel) + 11.223s (initrd) + 44.688s (userspace) = 57.657s
>     Startup finished in 1.721s (kernel) + 11.222s (initrd) + 44.194s (userspace) = 57.138s
>     Startup finished in 1.693s (kernel) + 11.250s (initrd) + 44.426s (userspace) = 57.370s
> 
>     # -fstack-protector
>     Startup finished in 1.705s (kernel) + 11.409s (initrd) + 43.563s (userspace) = 56.677s
>     Startup finished in 1.877s (kernel) + 11.137s (initrd) + 43.719s (userspace) = 56.734s
>     Startup finished in 1.708s (kernel) + 11.141s (initrd) + 43.628s (userspace) = 56.478s
> 
>     # no stack protector
>     Startup finished in 1.743s (kernel) + 11.190s (initrd) + 43.709s (userspace) = 56.643s
>     Startup finished in 1.763s (kernel) + 11.216s (initrd) + 43.767s (userspace) = 56.747s
>     Startup finished in 1.711s (kernel) + 11.283s (initrd) + 43.878s (userspace) = 56.873s
> 
> This patch introduces a configure option to disable the stack protector
> entirely, and conditional stack protector flag selection (in order, based on
> availability): -fstack-protector-strong, -fstack-protector, no stack protector.
> 
> Signed-off-by: Steven Noonan <snoonan@amazon.com>
> ---
>  configure | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
> 
> diff --git a/configure b/configure
> index 07b6be3..c9c0b2c 100755
> --- a/configure
> +++ b/configure
> @@ -147,6 +147,7 @@ audio_win_int=""
>  cc_i386=i386-pc-linux-gnu-gcc
>  libs_qga=""
>  debug_info="yes"
> +stack_protector=""
>  
>  # Don't accept a target_list environment variable.
>  unset target_list
> @@ -879,6 +880,10 @@ for opt do
>    ;;
>    --disable-werror) werror="no"
>    ;;
> +  --enable-stack-protector) stack_protector="yes"
> +  ;;
> +  --disable-stack-protector) stack_protector="no"
> +  ;;
>    --disable-curses) curses="no"
>    ;;
>    --enable-curses) curses="yes"
> @@ -1117,6 +1122,7 @@ echo "  --enable-sparse          enable sparse checker"
>  echo "  --disable-sparse         disable sparse checker (default)"
>  echo "  --disable-strip          disable stripping binaries"
>  echo "  --disable-werror         disable compilation abort on warning"
> +echo "  --disable-stack-protector disable GCC-provided stack protection"


Clang also supports stack protection AFAIK, so "GCC-provided" can be
removed here (or replaced by "compiler").


>  echo "  --disable-sdl            disable SDL"
>  echo "  --enable-sdl             enable SDL"
>  echo "  --disable-gtk            disable gtk UI"
> @@ -1298,9 +1304,15 @@ for flag in $gcc_flags; do
>      fi
>  done
>  
> -if compile_prog "-Werror -fstack-protector-all" "" ; then
> -    QEMU_CFLAGS="$QEMU_CFLAGS -fstack-protector-all"
> -    LIBTOOLFLAGS="$LIBTOOLFLAGS -Wc,-fstack-protector-all"
> +if test "$stack_protector" != "no" ; then
> +  gcc_flags="-fstack-protector-strong -fstack-protector"
> +  for flag in $gcc_flags; do
> +    if compile_prog "-Werror $flag" "" ; then
> +      QEMU_CFLAGS="$QEMU_CFLAGS $flag"
> +      LIBTOOLFLAGS="$LIBTOOLFLAGS -Wc,$flag"
> +      break
> +    fi
> +  done
>  fi
>  
>  # Workaround for http://gcc.gnu.org/PR55489.  Happens with -fPIE/-fPIC and
> 


Reviewed-by: Stefan Weil <sw@weilnetz.de>

I think this patch can be used as a base for further improvements (MinGW
specific settings, error handling when user's choice does not work).

Maybe you will have to resend the patch as a top level patch (don't use
the reply function of your mailer). As Paolo said, Anthony might
overwise be unable to pick it up with his scripts.

Regards
Stefan