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

William Tu u9012063 at gmail.com
Tue Oct 1 23:19:39 UTC 2019

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

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.


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