Re: [Qemu-devel] [PATCH] split c and cxx extra flags

[Bruno Dominguez <bru.dominguez@gmail.com>]

2017-06-06 10:28 GMT+01:00 Stefan Hajnoczi <stefanha@gmail.com>:
> On Fri, Jun 02, 2017 at 02:07:26PM +0100, Bruno Dominguez wrote:
>> There was no possibility to add specific cxx flags using the configure
>> file. So A new entrance has been created to support it.
>>
>> Duplication of information in configure and rules.mak. Taking
>> QEMU_CFLAGS and add them to QEMU_CXXFLAGS, now the value of
>> QEMU_CXXFLAGS is stored in config-host.mak, so there is no need for
>> it.
>>
>> The makefile for libvixl was adding flags for QEMU_CXXFLAGS in
>> QEMU_CFLAGS because of the addition in rules.mak. That was removed, so
>> adding them where it should be.
>>
>> -----
>> Signed-off-by: Bruno Dominguez <bru.dominguez@gmail.com>
>> -----
>
> Please follow the code submission guidelines:
> http://wiki.qemu.org/Contribute/SubmitAPatch
>
>  * The commit message (email subject) should have a prefix describing
>    the affected component.  Use "git log ./configure" for inspiration.
>    I suggest the following:
>
>      configure: split c and cxx extra flags
>
>  * Use git-format-patch(1) so that your patch applies cleanly.  Your
>    email has:
>
>    ----
>    Signed-off-by: ...
>    ----
>
>    This is not the format recognized by tools.  Instead the
>    Signed-off-by: should be part of the commit description (no '----')
>    and then a line with just three hyphens ('---') denotes the end of
>    the commit description:
>
>    Signed-off-by: ...
>    ---
>
>  * The email must not be line-wrapped since that breaks the patch.  If
>    you use git-send-email(1) to submit patches then this is taken care
>    of automatically.
>

ok, will give it another go.

>> @@ -1304,6 +1312,7 @@ Advanced options (experts only):
>>    --cxx=CXX                use C++ compiler CXX [$cxx]
>>    --objcc=OBJCC            use Objective-C compiler OBJCC [$objcc]
>>    --extra-cflags=CFLAGS    append extra C compiler flags QEMU_CFLAGS
>> +  --extra-cxxflags=CXXFLAGS append extra CXX compiler flags QEMU_CXXFLAGS
>
> For consistency with the --cxx= option description:
>
> s/CXX compiler/C++ compiler/
>

will do.

>> @@ -1489,37 +1498,6 @@ if test "$bogus_os" = "yes"; then
>>      error_exit "Unrecognized host OS $targetos"
>>  fi
>>
>> -# Check that the C++ compiler exists and works with the C compiler
>> -if has $cxx; then
>> -    cat > $TMPC <<EOF
>> -int c_function(void);
>> -int main(void) { return c_function(); }
>> -EOF
>> -
>> -    compile_object
>> -
>> -    cat > $TMPCXX <<EOF
>> -extern "C" {
>> -   int c_function(void);
>> -}
>> -int c_function(void) { return 42; }
>> -EOF
>> -
>> -    update_cxxflags
>> -
>> -    if do_cxx $QEMU_CXXFLAGS -o $TMPE $TMPCXX $TMPO $LDFLAGS; then
>> -        # C++ compiler $cxx works ok with C compiler $cc
>> -        :
>> -    else
>> -        echo "C++ compiler $cxx does not work with C compiler $cc"
>> -        echo "Disabling C++ specific optional code"
>> -        cxx=
>> -    fi
>> -else
>> -    echo "No C++ compiler available; disabling C++ specific optional code"
>> -    cxx=
>> -fi
>> -
>
> Why move this code?
>

the configure file adds "-fPIE -DPIE" to QEMU_CFLAGS around line 1570.
Where QEMU_CXXFLAGS is placed is not taken it, hence this flag is not
tested with the c++ compiler and breaks the build later on for not
existing. Because QEMU_CXXFLAGS was reassigned again in rules.mak this
was hidden.