Re: [Qemu-devel] [PATCH for-2.0] configure: use do_cc when checking for -fstack-protector support

[Peter Maydell]

On 11 April 2014 15:33, Alexey Kardashevskiy <address@hidden> wrote:
> On 04/12/2014 12:24 AM, Alexey Kardashevskiy wrote:
>> This helps. No idea why. Any ideas? :)
>>
>> @@ -1448,7 +1452,7 @@ done
>>  if test "$stack_protector" != "no" ; then
>>    gcc_flags="-fstack-protector-strong -fstack-protector-all"
>>    for flag in $gcc_flags; do
>> -    if do_cc $QEMU_CFLAGS -Werror $flag -c -o $TMPO $TMPC ; then
>> +    if do_cc $QEMU_CFLAGS -Werror $flag -c -o $TMPO $TMPC "" ; then
>>        QEMU_CFLAGS="$QEMU_CFLAGS $flag"
>>        LIBTOOLFLAGS="$LIBTOOLFLAGS -Wc,$flag"
>>        break

This change causes the do_cc to always fail (you can see the compiler
errors in the logs as it fails to find a file whose name is the empty string),
so it means we don't use the -fstack-protector arguments.

>>> /home/system/opt/cross/gcc-4.8.0-nolibc/powerpc64-linux/bin/../lib/gcc/powerpc64-linux/4.8.0/../../../../powerpc64-linux/bin/ld:
>>> cannot find -lssp_nonshared
>>> /home/system/opt/cross/gcc-4.8.0-nolibc/powerpc64-linux/bin/../lib/gcc/powerpc64-linux/4.8.0/../../../../powerpc64-linux/bin/ld:
>>> cannot find -lssp
>>> collect2: error: ld returned 1 exit status

If we do use the stack protector arguments then the next time
we try to do a configure test which does a link then it fails
like this, because your cross compile environment doesn't
have the stack-protector libraries in it. You should probably
add those, so you get the benefit of the stack protection, but
we can work around this in configure by doing both a compile
and a link check, as MST originally suggested. Patch to
follow shortly.

(Here's a linux perf tools patch which deals with a similar situation:
https://lkml.org/lkml/2010/1/11/117
)

thanks
-- PMM