[ovs-dev] [PATCH] m4: Fix 32bit build with 64bit version of libunwind-dev installed.

William Tu u9012063 at gmail.com
Wed Oct 2 16:14:54 UTC 2019


On Wed, Oct 02, 2019 at 06:46:36PM +0300, Ilya Maximets wrote:
> On 02.10.2019 17:46, Ben Pfaff wrote:
> >On Tue, Oct 01, 2019 at 06:40:10PM -0700, William Tu wrote:
> >>On Tue, Oct 1, 2019 at 4:19 PM William Tu <u9012063 at gmail.com> wrote:
> >>>
> >>>On Tue, Oct 01, 2019 at 08:29:41PM +0300, Ilya Maximets wrote:
> >>>>On 01.10.2019 19:56, Ben Pfaff wrote:
> >>>>>On Tue, Oct 01, 2019 at 07:46:10PM +0300, Ilya Maximets wrote:
> >>>>>>On 01.10.2019 19:17, Ben Pfaff wrote:
> >>>>>>>On Tue, Oct 01, 2019 at 02:22:20PM +0300, Ilya Maximets wrote:
> >>>>>>>>32 and 64 bit versions of libunwind-dev package can not be installed
> >>>>>>>>at the same time at least in Debian and Ubuntu.  AC_CHECK_LIB macro
> >>>>>>>>doesn't know if we have '-m32' in OVS_CFLAGS, so we need to
> >>>>>>>>additionally check for actual compiling possibility before enabling
> >>>>>>>>the feature.  Otherwise 'make' will fail due to inability to
> >>>>>>>>build with 64bit libunwind headers:
> >>>>>>>>
> >>>>>>>>      https://travis-ci.org/openvswitch/ovs/jobs/590580374
> >>>>>>>>
> >>>>>>>>      /usr/include/libunwind.h:23:28: fatal error:
> >>>>>>>>          libunwind-x86.h: No such file or directory
> >>>>>>>>
> >>>>>>>>CC: William Tu <u9012063 at gmail.com>
> >>>>>>>>Fixes: e2ed6fbeb18c ("fatal-signal: Catch SIGSEGV and print backtrace.")
> >>>>>>>>Signed-off-by: Ilya Maximets <i.maximets at ovn.org>
> >>>>>>>
> >>>>>>>I think there's some confusion here on the use of options.  CFLAGS is
> >>>>>>>for the user, OVS_CFLAGS is for the OVS configure script to use itself.
> >>>>>>>.cirrus.yml and .travis/linux-build.sh are setting OVS_CFLAGS, but they
> >>>>>>>should not because they are the "user", not the configure script.  If
> >>>>>>>they set CFLAGS, instead, I believe that there would be no problem here.
> >>>>>>>
> >>>>>>>See commit 95626395a3db ("build: Respect CFLAGS and LDFLAGS passed to
> >>>>>>>make") and the documentation it references.
> >>>>>>
> >>>>>>That's an interesting point.
> >>>>>>However, 'configure' script makes decision about building with libunwind
> >>>>>>and it needs to know  if we're going to build 32 or 64 bit binary to
> >>>>>>enable or disable the feature. Setting CFLAGS for configure script breaks
> >>>>>>it in a following way:
> >>>>>>
> >>>>>>$ CFLAGS='-m32' ./configure
> >>>>>>...
> >>>>>>checking for gcc... gcc
> >>>>>>checking whether the C compiler works... no
> >>>>>
> >>>>>Is this because the 32-bit C library isn't installed?  It should be easy
> >>>>>to fix with "sudo dnf install glibc-devel.i686" or the distro-specific
> >>>>>equivalent.
> >>>>
> >>>>Yes, you're right. It works after installation of gcc-multilib.
> >>>>
> >>>>I'll think about how to rework CI scripts tomorrow.
> >>>>
> >>>>>
> >>>>>I don't see how it's reasonable to run "configure" with a toolchain
> >>>>>different from the one we're going to use for building.  Adding -m32
> >>>>>changes the ABI and the API.
> >>>>>
> >>>>>My usual way to do this is actually to use CC="gcc -m32".  That way the
> >>>>>-m32, which is important, can't get separated at all!
> >>>
> >>>Thanks Ben and Ilya,
> >>>
> >>>I don't have a good solution, on my Xenial system, if I do 32-bit build
> >>>
> >>>   apt-get install libunwind-dev:i386
> >>>   CC="gcc -m32" ./configure
> >>>
> >>>then it correctly detects libunwind and pass, for x86_64, I have to
> >>>
> >>>   apt-get remove libunwind-dev:i386
> >>>   apt-get install libunwind-dev
> >>>   ./configure
> >>>
> >>>so like Ilya mentioned, the 32 and 64 bit libunwind-dev can not be installed
> >>>at the same time. To pass travis, we need to check whether it has '-m32' or not,
> >>>then install different libunwind-dev package.
> >>>
> >>>I'm also ok with disabling this feature on 32-bit system.
> >>>
> >>>Regards,
> >>>William
> >>>
> >>Hi,
> >>
> >>How about this fix? So for 32-bit system, we have to install libunwind-dev:i386,
> >>in the meantime the libunwind-dev for 64-bit will be removed automatically.
> >>I tested it and passed.
> >>https://travis-ci.org/williamtu/ovs-travis/builds/592323952
> >
> >Acked-by: Ben Pfaff <blp at ovn.org>
> >
> >It might be worth waiting for Ilya's feedback, though.
> 
> Thanks William and Ben,
> 
> I think that we need both solutions.  Conditional installing of
> 32bit library will allow us to test with it.  However, I think,
> that we need to eliminate usage of OVS_CFLAGS in our CI scripts
> too, because this gives a bad example for users.  I personally
> always used OVS_CFLAGS for passing '-Wno-cast-align' while
> building with clang and dpdk, probably, just because first time
> I saw that in CI scripts. I'm working on the fix.
> 
> The change itself is fine. One small nit is that maybe it worth
> to move this command to linux-prepare.sh script to keep all the
> external software related stuff in the same place?

OK, that makes sense.
I will prepare the patch.

Regards,
William


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