From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43998) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1erlwd-0008NU-88 for qemu-devel@nongnu.org; Fri, 02 Mar 2018 09:46:01 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1erlwa-0007Zw-4H for qemu-devel@nongnu.org; Fri, 02 Mar 2018 09:45:59 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:40368 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1erlwZ-0007Zg-Ui for qemu-devel@nongnu.org; Fri, 02 Mar 2018 09:45:56 -0500 References: <20180302013007.11827-1-eblake@redhat.com> From: Eric Blake Message-ID: Date: Fri, 2 Mar 2018 08:45:46 -0600 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PULL v2 00/30] QAPI patches for 2018-03-01 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: QEMU Developers On 03/02/2018 08:34 AM, Peter Maydell wrote: > On 2 March 2018 at 14:05, Eric Blake wrote: >> On 03/02/2018 06:38 AM, Peter Maydell wrote: >>> This produces a huge pile of warnings from my OSX toolchain. >>> >>> When running ar on libqemuutil.a: >>> AR libqemuutil.a >>> >>> /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib: >>> file: libqemuutil.a(qapi-types.o) has no symbols >> >> >> Part of this change was moving the location of the generated ./qapi-types.c >> to qapi/qapi-types.c. Could it be that you are doing an incremental build, >> rather than a clean build, and the compiler is picking up the stale version >> of the file rather than its new location? > > I am doing an incremental build, yes. That needs to work, not break... And since it was warnings and you picked up qapi/qapi-events.c, it looks like it does work; phew. > >>> I had a look at the autogenerated .c files on my Linux build, and they >>> seem to consist only of a bunch of #includes. Why are we not generating >>> any code here? > >> But I just checked, and at least for qapi/qapi-types.c, the generated file >> IS just a list of includes; and in fact, it looks like all of the mentioned >> files are in that boat (for example, qapi/transaction.json has no events, so >> qapi/qapi-events-transaction.c being empty makes sense). > >> I know that some compilers are picky about that. > > Yes, I think this is what is causing the problem. Okay, we've narrowed in on root cause, and it's now just a matter of finding the magic formula to shut up the toolchain. > >> Is a typedef enough to >> cause the compiler to have something to compile without warnings? > > Given that the warnings are coming from nm and ranlib, anything that > doesn't actually cause a symbol to be put into the .o file isn't going > to be enough I suspect. As I mentioned on IRC, gnulib has used typedefs to prevent empty files before: https://git.savannah.gnu.org/cgit/gnulib.git/commit/lib/binary-io.c?id=c5d07ce91a8ad51591154450442fa4376441fdfa https://lists.gnu.org/archive/html/bug-gnulib/2015-10/msg00019.html https://lists.gnu.org/archive/html/bug-gnulib/2004-07/msg00029.html >> + def _bottom(self, fname): >> + return mcgen(''' >> +/* Dummy typedef to prevent empty .o file */ >> +typedef int %(name)s; >> +''', >> + name=c_name(fname)) >> + >> >> class QAPIGenH(QAPIGenC): > > I just tested this, and it isn't sufficient. Oh well, we'll have to burn actual storage, then. My next try is: static char dummy_%(name)s; perhaps with an __attribute__((unused)); if that gets by without warnings on the toolchains I have available, it should hopefully be stronger than just the typedef and therefore enough for your toolchain. I'll submit v3 shortly. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org