Re: [PULL 0/1] Libslirp update

["Marc-André Lureau" <marcandre.lureau@gmail.com>]

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Hi

On Tue, Aug 3, 2021 at 12:55 AM Peter Maydell <peter.maydell@linaro.org>
wrote:

> On Mon, 2 Aug 2021 at 19:58, Marc-André Lureau
> <marcandre.lureau@gmail.com> wrote:
> >
> > Hi Peter
> >
> > On Sun, Aug 1, 2021 at 4:10 PM Peter Maydell <peter.maydell@linaro.org>
> wrote:
> >>
> >> On Wed, 28 Jul 2021 at 16:47, Marc-André Lureau
> >> <marcandre.lureau@gmail.com> wrote:
> >> > I wish my previous pull request with the submodule change would
> >> > receive more help or attention, as I either couldn't reproduce the
> >> > failure (neither CI) or it was just some one-time warnings due to the
> >> > transition...
> >>
> >> Well, I reported the failures back to you. I can't do a lot more,
> >> because libslirp development is now much more opaque to me because
> >> it doesn't happen in-tree. So instead of "some small change happens and
> >> we pick up issues with it early", you have to deal with all of
> >> the accumulated problems at once when you update the submodule :-(
> >>
> >> rc2 is on Tuesday, so we're starting to run short on time to
> >> get an updated slirp in for 6.1.
> >>
> >
> > Do you mind checking the https://github.com/elmarco/qemu/tree/libslirp
> branch?
> >
> > From https://mail.gnu.org/archive/html/qemu-devel/2021-06/msg00031.html,
> there would still be the one-time warnings from git, but osx and dist error
> should be gone.
>
> Yep, I still see the git "warning: unable to rmdir 'slirp': Directory
> not empty", but I think we can ignore that.
>
> I also see
> config-host.mak is out-of-date, running configure
>   GIT     ui/keycodemapdb meson tests/fp/berkeley-testfloat-3
> tests/fp/berkeley-softfloat-3 dtc capstone slirp
> warn: ignoring non-existent submodule slirp
>
> but I think that is also a one-off?
>

yes


> > Only one left as a mystery is the Ubuntu-ASAN link issue.
>
> This one is still here:
>
> subprojects/libslirp/libslirp.so.0.3.1.p/src_arp_table.c.o: In
> function `arp_table_add':
>
> /mnt/nvmedisk/linaro/qemu-for-merges/build/clang/../../subprojects/libslirp/src/arp_table.c:51:
> undefined reference to `__ubsan_handle_type_mismatch_v1'
>
> /mnt/nvmedisk/linaro/qemu-for-merges/build/clang/../../subprojects/libslirp/src/arp_table.c:51:
> undefined reference to `__ubsan_handle_type_mismatch_v1'
>
> when building the subprojects/libslirp/libslirp.so.0.3.1
>
> configure options:
> '../../configure' '--cc=clang' '--cxx=clang++' '--enable-gtk'
> '--extra-cflags=-fsanitize=undefined  -fno-sanitize=shift-base
> -Werror'
>

I am not able to reproduce. Could you check the value of default_library
for libslirp when you run "meson configure". It should be "static".

I tested with "make vm-build-ubuntu.amd64", with tests/vm/ubuntu.amd64:
import sys
import basevm
import ubuntuvm

DEFAULT_CONFIG = {
    'install_cmds' : "apt-get update,"\
                     "apt-get build-dep -y qemu,"\
                     "apt-get install -y libfdt-dev language-pack-en
ninja-build clang",
}

class UbuntuX64VM(ubuntuvm.UbuntuVM):
    name = "ubuntu.amd64"
    arch = "x86_64"
    image_link="https://cloud-images.ubuntu.com/releases/bionic/"\
               "release-20191114/ubuntu-18.04-server-cloudimg-amd64.img"

image_sha256="0c55fded766f3e4efb082f604ed71dd58c8e81f04bd1a66b4ced80ad62617547"
    BUILD_SCRIPT = """
        set -e;
        cd $(mktemp -d);
        sudo chmod a+r /dev/vdb;
        tar -xf /dev/vdb;
        ./configure {configure_opts} --cc=clang --cxx=clang++
--host-cc=clang --extra-cflags='-fsanitize=undefined
 -fno-sanitize=shift-base -Werror'
        make --output-sync {target} -j{jobs} {verbose};
    """

if __name__ == "__main__":
    sys.exit(basevm.main(UbuntuX64VM, DEFAULT_CONFIG))



> This happens because (as noted in the clang documentation for the
> sanitizer: https://clang.llvm.org/docs/AddressSanitizer.html)
> when linking a shared library with the sanitizers, clang does not
> link in the sanitizer runtime library. That library is linked in
> with the executable, and the shared library's references to the
> sanitizer runtime functions are satisfied that way. However
> you/meson are building libslirp.so with -Wl,--no-undefined
> so the link of the .so fails.
> (This does not happen with gcc, because gcc chose to make the
> default for sanitizers to be to link against a shared libasan,
> not a static one, the reverse of clang's default.)
>
> What I don't understand is why we're building the .so at all.
> I just tried a fresh build with
> '../../configure' '--cc=clang' '--cxx=clang++' '--enable-gtk'
> '--enable-sanitizers'
> to check that telling configure (and possibly thus meson) about
> the sanitizers more directly still demonstrated the problem:
> but that sidesteps it because it never builds the .so.
> My other build directories (the ones that do plain old gcc
> builds with no sanitizer) seem to have built the .so file
> as well, though, so this isn't related to either clang or to
> the sanitizers -- meson just doesn't seem to be consistent
> about what we build.
>
> A related meson bug:
> https://github.com/mesonbuild/meson/issues/764
> (which was closed by just making meson warn if you tell it
> to both use --no-undefined (which is the default) and to use
> the sanitizer.)
>
> The ideal fix seems to me to be to figure out why we're
> building the libslirp .so and not do that.
>
> A simple fix/workaround would be to set "b_lundef = false" in
> default_options in your meson.build (which will suppress the
> -Wl,--no-undefined option). That does mean you won't get
> any warnings if you accidentally make libslirp use a function
> that is provided by the QEMU executable, I suppose.
>
>
What if you pass --extra-ldflags='-fsanitize=undefined' then?

thanks

-- 
Marc-André Lureau

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