[llvm-dev] llvm-strip creates unloadable shared objects on linux-armv7hf

Thu Oct 31 05:15:54 PDT 2019

Thanks for your contribution! I'm sure I can speak for all of us when I say
that we look forward to more contributions from you, if you see anything
else you'd like to work on.

James

On Thu, 31 Oct 2019 at 12:05, Tobias Hieta via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Everyone,
>
> Just to close this loop, the patch was accepted into master today:
>
> https://github.com/llvm/llvm-project/commit/fb4a55010ee9bd03720609c8542f770775576fc8
>
> Thanks for everyone guiding me!
>
> Tobias
>
> On Fri, Oct 18, 2019 at 8:41 PM Tobias Hieta <tobias at plexapp.com> wrote:
> >
> > Jordan,
> >
> > I have sent the patch via Phabricator: https://reviews.llvm.org/D69188
> >
> > Let me know if I got it right.
> >
> > -- Tobias
> >
> > On Thu, Oct 17, 2019 at 7:12 PM Jordan Rupprecht <rupprecht at google.com>
> wrote:
> > >
> > > Tobias,
> > > I don't have much experience with ARM, but from your report and
> Peter's explanation of why LLD does it, I agree we should be consistent
> with LLD and keep the section.
> > >
> > > From my skimming of the LLD sources, it looks like we keep arm
> attributes section based on the section type being SHT_ARM_ATTRIBUTES, not
> on the name being ".ARM.attributes". Other than that, this change seems
> good to accept.
> > >
> > > Feel free to send a patch! (btw, my review handle is rupprecht, not
> rupprect).
> > >
> > > On Thu, Oct 17, 2019 at 5:29 AM Peter Smith via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> > >>
> > >> Hello Tobias,
> > >>
> > >> I think that looks reasonable to me, I think it will be down to the
> > >> llvm-objcopy team whether they want to make .ARM.attributes a special
> > >> case or not. The best way to find out is to submit a patch, citing the
> > >> problems with old versions of libc, I'd expect that you'll need to add
> > >> a test case for the patch to be accepted. To do that it is probably
> > >> best to look at the existing tests for llvm-strip and try and copy
> > >> them. The test could be as simple as generating a binary with a
> > >> section of type SHT_ARM_ATTRIBUTES and checking that strip didn't
> > >> remove it. These tests sometimes use yaml2obj to generate an ELF file
> > >> without needing a compiler and linker. Running the tests should be as
> > >> simple as ninja check-llvm or make check-llvm depending on whether you
> > >> used ninja or make when building llvm. If you want to run just one
> > >> test then you can use bin/llvm-lit -v -a /path/to/test.s (from your
> > >> build directory).
> > >>
> > >> The instructions on how to contribute are in
> > >> https://llvm.org/docs/DeveloperPolicy.html the people that I know
> have
> > >> been active in llvm-objdump are MaskRay (Fangrui Song), rupprect
> > >> (Jordan Rupprecht), grimar (George Rimar). If you include these people
> > >> on the reviewers then I'm sure they'll be able to add anyone else that
> > >> they think would be interested.
> > >>
> > >> Hope this helps
> > >>
> > >> Peter
> > >>
> > >> On Thu, 17 Oct 2019 at 12:53, Tobias Hieta <tobias at plexapp.com>
> wrote:
> > >> >
> > >> > Hello Peter,
> > >> >
> > >> > I was able to fix this issue with this simple patch against
> llvm-objcopy:
> > >> >
> > >> > diff --git a/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
> > >> > b/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
> > >> > index dd6a7d7e14b..c0dfd3a9838 100644
> > >> > --- a/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
> > >> > +++ b/llvm/tools/llvm-objcopy/ELF/ELFObjcopy.cpp
> > >> > @@ -503,6 +503,8 @@ static Error replaceAndRemoveSections(const
> > >> > CopyConfig &Config, Object &Obj) {
> > >> > return false;
> > >> > if (StringRef(Sec.Name).startswith(".gnu.warning"))
> > >> > return false;
> > >> > + if (StringRef(Sec.Name).startswith(".ARM.attributes"))
> > >> > + return false;
> > >> > if (Sec.ParentSegment != nullptr)
> > >> > return false;
> > >> > return (Sec.Flags & SHF_ALLOC) == 0;
> > >> >
> > >> > Is this a good way of fixing the issue? Happy to read up on how to
> > >> > submit patches if you think this is the way to go.
> > >> >
> > >> > -- Tobias
> > >> >
> > >> >
> > >> > On Thu, Oct 17, 2019 at 12:27 PM Peter Smith <
> peter.smith at linaro.org> wrote:
> > >> > >
> > >> > > It is possible that it was present in older versions of glibc,
> with
> > >> > > the limited time I've got for archaeology I found
> > >> > > https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1712938
> > >> > > My change in LLD was https://reviews.llvm.org/D27718 although it
> > >> > > doesn't help much.
> > >> > >
> > >> > > You may be able to follow the bread crumb trail from the launchpad
> > >> > > bug. Good luck!
> > >> > >
> > >> > > Peter
> > >> > >
> > >> > > On Thu, 17 Oct 2019 at 10:59, Tobias Hieta <tobias at plexapp.com>
> wrote:
> > >> > > >
> > >> > > > Peter,
> > >> > > >
> > >> > > > Thanks for your detailed response. I am not 100% sure on what
> libc we
> > >> > > > are using here, it's a netgear NAS device. We publish Plex for
> > >> > > > multiple NAS vendors devices and their toolchain always seems
> to lag
> > >> > > > behind a bit, which is why we invested in building our own
> toolchain
> > >> > > > based on LLVM tools.
> > >> > > >
> > >> > > > Does seem to be glibc though:
> > >> > > > ii libc-bin 2.19-18+deb8u10.netgear1 armel GNU C Library:
> Binaries
> > >> > > >
> > >> > > > Maybe it's just because it's older why this happens?
> > >> > > >
> > >> > > > Thanks,
> > >> > > > Tobias
> > >> > > >
> > >> > > > On Thu, Oct 17, 2019 at 11:25 AM Peter Smith <
> peter.smith at linaro.org> wrote:
> > >> > > > >
> > >> > > > > Hello Tobias,
> > >> > > > >
> > >> > > > > Does your system happen to be using eglibc? I ran into this
> problem on
> > >> > > > > an Ubuntu 14.04 system and it was down to the eglibc dynamic
> loader
> > >> > > > > using the .ARM.attributes section when performing dlopen.
> Strictly
> > >> > > > > speaking the .ARM.attributes section is only defined for
> relocatable
> > >> > > > > objects, the ABI says that their presence in executables or
> dynamic
> > >> > > > > loaders is neither required or forbidden, so it is somewhat
> risky for
> > >> > > > > any portable program to depend on their presence.
> > >> > > > >
> > >> > > > > Since eglibc was merged back into glibc this dependency on
> > >> > > > > .ARM.attributes went away. For LLD we took the position that
> it was
> > >> > > > > worth keeping the .ARM.attributes to placate eglibc, as this
> was more
> > >> > > > > likely to be encountered 2 years ago. I've not got a strong
> position
> > >> > > > > on llvm-strip, in theory it should be strippable from
> executable and
> > >> > > > > shared libraries, but there may be a case that eglibc is
> important
> > >> > > > > enough to not strip by default.
> > >> > > > >
> > >> > > > > Peter
> > >> > > > >
> > >> > > > > On Thu, 17 Oct 2019 at 10:16, Tobias Hieta via llvm-dev
> > >> > > > > <llvm-dev at lists.llvm.org> wrote:
> > >> > > > > >
> > >> > > > > > Hello Rui,
> > >> > > > > >
> > >> > > > > > Thanks for your reply. I tried with the keep-section
> argument and that
> > >> > > > > > made the shared library work.
> > >> > > > > >
> > >> > > > > > Should these sections be kept around by default maybe?
> > >> > > > > >
> > >> > > > > > -- Tobias
> > >> > > > > >
> > >> > > > > > On Thu, Oct 17, 2019 at 11:06 AM Rui Ueyama <
> ruiu at google.com> wrote:
> > >> > > > > > >
> > >> > > > > > > One thing I noticed is that llvm-strip seemed to remove a
> .ARM.attributes section. Can you try --keep-section=.ARM.attributes to tell
> to the command to keep the section?
> > >> > > > > > >
> > >> > > > > > > On Thu, Oct 17, 2019 at 5:37 PM Tobias Hieta via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > >> > > > > > >>
> > >> > > > > > >> Hello,
> > >> > > > > > >>
> > >> > > > > > >> Recently we tried to streamline our toolchain by
> removing some GNU
> > >> > > > > > >> tools with LLVM tools to avoid having multiple copies of
> strip, nm, ar
> > >> > > > > > >> and similar tools. Today we ran into a really strange
> issue where
> > >> > > > > > >> shared objects where not loadable.
> > >> > > > > > >>
> > >> > > > > > >> We where able to track this down to llvm-strip with
> default arguments
> > >> > > > > > >> creating a shared object that doesn't load correctly. It
> works if we
> > >> > > > > > >> switch from not passing args to llvm-strip to pass
> -strip-all-gnu
> > >> > > > > > >>
> > >> > > > > > >> I built bzip2 and libbz2.so to show this case here:
> > >> > > > > > >>
> https://1drv.ms/u/s!Amjta5FRkBbbkiz14aHTRJe03LlL?e=2mGvTN
> > >> > > > > > >>
> > >> > > > > > >> This is the error we got by using the stripped shared
> object with
> > >> > > > > > >> llvm-strip -strip-all:
> > >> > > > > > >>
> > >> > > > > > >> admin at Netgear-RN212:~/b$ LD_PRELOAD=./libbz2.so.all
> ./bzip2
> > >> > > > > > >> ERROR: ld.so: object './libbz2.so.all' from LD_PRELOAD
> cannot be
> > >> > > > > > >> preloaded (cannot open shared object file): ignored.
> > >> > > > > > >> ./bzip2: error while loading shared libraries:
> libbz2.so: cannot open
> > >> > > > > > >> shared object file: No such file or directory
> > >> > > > > > >>
> > >> > > > > > >> And with strip-all-gnu it works:
> > >> > > > > > >> admin at Netgear-RN212:~/b$ LD_PRELOAD=./libbz2.so.all_gnu
> ./bzip2
> > >> > > > > > >> bzip2: I won't write compressed data to a terminal.
> > >> > > > > > >> bzip2: For help, type: `bzip2 --help'.
> > >> > > > > > >>
> > >> > > > > > >> This only seems to happen on Linux-armv7hf - we haven't
> seen this on
> > >> > > > > > >> any of the intel platforms.
> > >> > > > > > >>
> > >> > > > > > >> Thanks,
> > >> > > > > > >> Tobias
> > >> > > > > > >> _______________________________________________
> > >> > > > > > >> LLVM Developers mailing list
> > >> > > > > > >> llvm-dev at lists.llvm.org
> > >> > > > > > >> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> > >> > > > > > _______________________________________________
> > >> > > > > > LLVM Developers mailing list
> > >> > > > > > llvm-dev at lists.llvm.org
> > >> > > > > > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> > >> _______________________________________________
> > >> LLVM Developers mailing list
> > >> llvm-dev at lists.llvm.org
> > >> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> _______________________________________________
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