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Re: Adding configure flag

On 22 October 2015 at 00:21, Aurelio Remonda wrote:
> First of all, thank you so much for the quick reply! I still have some
> questions if you don't mind! :)


> On Wed, Oct 21, 2015 at 5:25 PM, Jonathan Wakely <> wrote:
>> On 21 October 2015 at 20:37, Aurelio Remonda wrote:
>>> Hi, im trying to add a configure flag to the libstdc++ for a feature
>>> I'm testing. This flag, if enabled, would define a C macro that I'd be
>>> using in
>>> I was doing some research and i believe i need to edit
>>> and acinclude.m4 on the libstdc++-v3 directory. Is this correct?
>>> I also need to run autoconf to regenerate the libstdc++-v3 configure
>>> script, right?
>> Yes. I use autoreconf to ensure all relevant files are regenerated
>> (using autoreconf doesn't work for all of GCC, but it does for
>> libstdc++).
>>> Do i need to make changes on the file in the top gcc
>>> directory? Or can i create the flag and do the configure and make on
>>> the libstdc++-v3 directory so it's ready for when I compile all of
>>> gcc?
>> Just in libstdc++-v3
> Ok but, that means that i will have to do configure and make on libstdc++
> and then compile gcc? or just make the changes, the autoreconf and then
> when i compile gcc the libstdc++ will be compiled with my changes?

When you compile gcc the libstdc++ will be compiled with your changes.

>>> On a related subject: right now, I've added the following line to the
>>> libstdc++v3's
>>> Also, I added the following to libstdc++v3's acinclude.m4:
>>>   GLIBCXX_ENABLE(new-opnt-if,$1,,[enable if on new_opnt instead of while])
>>>   if test $enable_new_opnt_if = yes; then
>>>         [Define is new_opnt will be used instead of while.])
>>>   fi
>>>   AC_MSG_CHECKING([for enabled if])
>> This message isn't very helpful.
> This is just a test, the message is just for me for now.

OK, just checking :-)

>>>   AC_MSG_RESULT([$enable_new_opnt_if])
>>> ])
>>> And on gcc top directory
>>> [AS_HELP_STRING([--enable-new-opnt-if],
>>>     [enable if on new_opnt instead of while])],
>>> [], [enable_new_opnt_if=yes])
>>> AC_SUBST(enable_multilib)
>> That shouldn't be there.
>> That description of the option is useless to end users anyway. Instead
>> it should be documented in libstdc++-v3/doc/xml/manual/configure.xml
>>> As you can see, I've hardcoded this option as "yes" to test it.
>>> However, I can't seem to make it work: in, I still can't
>>> see the macro defined. Am I doing something wrong?
>> It looks like you've hardcoded it to no, in libstdc++-v3/
>> Try using autoreconf, to make sure is regenerated
>> (although I think autoconf should do that anyway).
>> Try either changing the default in libstdc++-v3/ or using
>> --enable-new-opnt-if explicitly.
> I did try it with --enable-new-opnt-if when i configure gcc, that should replace
> the harcored "no" right?

Yes, it should.

When libstdc++ is built you should see it print "checking for enabled
if" (and you should be able to search for that in the
$target/libstdc++-v3/config.log file)

And then you should see you macro in

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