[llvm-dev] Building llvm with clang and lld on arm and the llvm arm backend relocation on position independent code

Peter Smith via llvm-dev llvm-dev at lists.llvm.org
Wed Jun 28 09:36:03 PDT 2017 

Yes it should cover the following relocations:
R_ARM_CALL (ARM BL/BLX)
R_ARM_JUMP24 (ARM B)
R_ARM_THM_CALL (Thumb BL/BLX)
R_ARM_THM_JUMP19 (Thumb conditional B<cc>.w)
R_ARM_THM_JMP24 (Thumb unconditional B.w)

Peter


On 28 June 2017 at 17:31, Alessandro Pistocchi <apukfreelance at gmail.com> wrote:
> Oh, so it looks like I hit a bit of a wall there :-) I’ll take a look thanks.
>
> That bug talks about R_ARM_THM_CALL which I assume are thumb related.
>
> Will your implementation fix also R_ARM_CALL errors?
>
>> On 28 Jun 2017, at 17:15, Peter Smith <peter.smith at linaro.org> wrote:
>>
>> Hello Alessandro,
>>
>> The LLD ARM port doesn't currently support range extension thunks,
>> these are needed to extend the range of ARM branch relocations when
>> the size of the executable instructions exceeds the maximum branch
>> range.
>>
>> I have an implementation in review but it is a fairly large change so
>> it may take some time to get through the review process, I've raised
>> https://bugs.llvm.org/show_bug.cgi?id=33612 that has a link to the
>> Phab reviews. If you are willing to build your own lld with additional
>> changes, you might be able to test out those patches.
>>
>> Good luck
>>
>> Peter
>>
>> On 28 June 2017 at 17:09, Alessandro Pistocchi <apukfreelance at gmail.com> wrote:
>>>
>>>> On 27 Jun 2017, at 13:25, Peter Smith <peter.smith at linaro.org> wrote:
>>>>
>>>> Hello Alessandro,
>>>>
>>>> Despite the statement in the HowToCrossCompileLLVM guide "If you’re
>>>> using Clang as the cross-compiler, there is a problem in the LLVM ARM
>>>> back-end that is producing absolute relocations on
>>>> position-independent code (R_ARM_THM_MOVW_ABS_NC), so for now, you
>>>> should disable PIC:" I can't find an existing upstream PR or any
>>>> record that this has been fixed. If the ARM backend is still producing
>>>> an R_ARM_THM_MOVW_ABS_NC relocation when -fpic is given as an option
>>>> then it would be great to get a small reproducible example in a new
>>>> PR, or if there is one already to update it.
>>>>
>>>> The last time I ran into this error when trying to cross compile was
>>>> that a dependency not compiled by clang (libtinfo.a) library contained
>>>> an R_ARM_THM_MOVW_ABS_NC relocation. I don't think that this is the
>>>> fault of clang/llvm though, I think it was my fault in installing a
>>>> non pic compiled version of libtinfo.a (I'm still trying to learn how
>>>> Ubuntu multilibs work).
>>>>
>>>> Would it be possible for you to share the details of which objects
>>>> contain the R_ARM_THM_MOVW_ABS_NC relocations when compiled -fpic?
>>>
>>> Hi, the errors I get do not seen to mention R_ARM_THM_MOVW_ABS_NC.
>>>
>>> The errors are “relocation R_ARM_CALL out of range”.
>>>
>>> Today I recompiled everything from scratch with -fPIC to make sure I had no library compiled without it and I still get the same errors.
>>>
>>> Sorry, I could not find any trivial code that has the same issue yet.
>>>
>>> Following is the output of the compilation process:
>>>
>>> yawmoo at yawmoo-MRNM3AP:~/Desktop/clfs/sources/llvm-build-native-with-lld$ cmake --build .
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>>> [ 85%] Linking CXX executable ../../../../bin/clang
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCAliasAnalysis.cpp:(function llvm::Pass* llvm::callDefaultCtor<llvm::objcarc::ObjCARCAAWrapperPass>()): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCAliasAnalysis.cpp:(function llvm::Pass* llvm::callDefaultCtor<llvm::objcarc::ObjCARCAAWrapperPass>()): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/tools/clang/lib/StaticAnalyzer/Core/CallEvent.cpp:(function clang::ento::CXXDestructorCall* clang::ento::CallEventManager::create<clang::ento::CXXDestructorCall, clang::CXXDestructorDecl const*, clang::Stmt const*, clang::ento::MemRegion const*, bool>(clang::CXXDestructorDecl const*, clang::Stmt const*, clang::ento::MemRegion const*, bool, llvm::IntrusiveRefCntPtr<clang::ento::ProgramState const>, clang::LocationContext const*)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCAliasAnalysis.cpp:(function llvm::Pass* llvm::callDefaultCtor<llvm::objcarc::ObjCARCAAWrapperPass>()): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCAliasAnalysis.cpp:(function llvm::Pass* llvm::callDefaultCtor<llvm::objcarc::ObjCARCAAWrapperPass>()): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCAliasAnalysis.cpp:(function llvm::Pass* llvm::callDefaultCtor<llvm::objcarc::ObjCARCAAWrapperPass>()): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCAnalysisUtils.cpp:(function llvm::cl::opt<bool, true, llvm::cl::parser<bool> >::opt<char [21], llvm::cl::desc, llvm::cl::LocationClass<bool>, llvm::cl::initializer<bool> >(char const (&) [21], llvm::cl::desc const&, llvm::cl::LocationClass<bool> const&, llvm::cl::initializer<bool> const&)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCAnalysisUtils.cpp:(function llvm::cl::opt<bool, true, llvm::cl::parser<bool> >::opt<char [21], llvm::cl::desc, llvm::cl::LocationClass<bool>, llvm::cl::initializer<bool> >(char const (&) [21], llvm::cl::desc const&, llvm::cl::LocationClass<bool> const&, llvm::cl::initializer<bool> const&)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCAnalysisUtils.cpp:(function llvm::cl::opt<bool, true, llvm::cl::parser<bool> >::opt<char [21], llvm::cl::desc, llvm::cl::LocationClass<bool>, llvm::cl::initializer<bool> >(char const (&) [21], llvm::cl::desc const&, llvm::cl::LocationClass<bool> const&, llvm::cl::initializer<bool> const&)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCAnalysisUtils.cpp:(function _GLOBAL__sub_I_ObjCARCAnalysisUtils.cpp): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCInstKind.cpp:(function llvm::objcarc::operator<<(llvm::raw_ostream&, llvm::objcarc::ARCInstKind)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCInstKind.cpp:(function llvm::objcarc::operator<<(llvm::raw_ostream&, llvm::objcarc::ARCInstKind)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCInstKind.cpp:(function llvm::objcarc::GetFunctionClass(llvm::Function const*)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/tools/clang/lib/StaticAnalyzer/Core/CallEvent.cpp:(function clang::ento::CXXDestructorCall* clang::ento::CallEventManager::create<clang::ento::CXXDestructorCall, clang::CXXDestructorDecl const*, clang::Stmt const*, clang::ento::MemRegion const*, bool>(clang::CXXDestructorDecl const*, clang::Stmt const*, clang::ento::MemRegion const*, bool, llvm::IntrusiveRefCntPtr<clang::ento::ProgramState const>, clang::LocationContext const*)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCInstKind.cpp:(function llvm::objcarc::GetFunctionClass(llvm::Function const*)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCInstKind.cpp:(function llvm::objcarc::GetFunctionClass(llvm::Function const*)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCInstKind.cpp:(function llvm::objcarc::GetFunctionClass(llvm::Function const*)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCInstKind.cpp:(function llvm::objcarc::GetFunctionClass(llvm::Function const*)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCInstKind.cpp:(function llvm::objcarc::GetFunctionClass(llvm::Function const*)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: /home/yawmoo/Desktop/clfs/sources/llvm/lib/Analysis/ObjCARCInstKind.cpp:(function llvm::objcarc::GetFunctionClass(llvm::Function const*)): relocation R_ARM_CALL out of range
>>> /home/yawmoo/Desktop/clfs/llvm-cross-tools-lld/bin/ld.lld: error: too many errors emitted, stopping now (use -error-limit=0 to see all errors)
>>> clang-5.0: error: linker command failed with exit code 1 (use -v to see invocation)
>>> tools/clang/tools/driver/CMakeFiles/clang.dir/build.make:227: recipe for target 'bin/clang-5.0' failed
>>> make[2]: *** [bin/clang-5.0] Error 1
>>> CMakeFiles/Makefile2:11670: recipe for target 'tools/clang/tools/driver/CMakeFiles/clang.dir/all' failed
>>> make[1]: *** [tools/clang/tools/driver/CMakeFiles/clang.dir/all] Error 2
>>> Makefile:149: recipe for target 'all' failed
>>> make: *** [all] Error 2
>>> yawmoo at yawmoo-MRNM3AP:~/Desktop/clfs/sources/llvm-build-native-with-lld$
>>>
>>>
>>>>
>>>> Peter
>>>>
>>>> On 27 June 2017 at 11:47, Alessandro Pistocchi via llvm-dev
>>>> <llvm-dev at lists.llvm.org> wrote:
>>>>>
>>>>> On 26 Jun 2017, at 16:25, Rui Ueyama <ruiu at google.com> wrote:
>>>>>
>>>>> On Sun, Jun 25, 2017 at 6:40 AM, Alessandro Pistocchi via llvm-dev
>>>>> <llvm-dev at lists.llvm.org> wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> I am trying to build a completely GNU free linux toolchain for the
>>>>>> raspberry pi.
>>>>>>
>>>>>> I successfully managed to compile llvm and clang for armv7 hard float (
>>>>>> both as a cross compiler and as a native compiler ) together with the
>>>>>> following:
>>>>>>
>>>>>> Llvm with clang and lld
>>>>>> Clang builtins
>>>>>> Musl libc
>>>>>> libc++, libc++abi, libunwind
>>>>>>
>>>>>> All works well with the only thing to notice being the need to use -fPIC
>>>>>> in order to access some library functions when my own c/c++ programs access
>>>>>> those functions.
>>>>>>
>>>>>> The fact seems to be that musl libc exports some symbols as protected (
>>>>>> probably correctly ) and lld ( probably correctly ) says it cannot preempt
>>>>>> those symbols.
>>>>>> For this reason I seem to have to use -fPIC in the C and CXX flags but
>>>>>> everything seems to work ok.
>>>>>
>>>>>
>>>>> Is this the same problem mentioned in
>>>>> https://bugs.llvm.org/show_bug.cgi?id=32425?
>>>>>
>>>>>
>>>>> My aim is to build llvm+clang+lld using llvm+clang+lld on arm ( using musl,
>>>>> libc++, libc++abi, libunwind and the clang builtins, no gcc runtime at all
>>>>> ).
>>>>>
>>>>> I think the fact that lld cannot preempt some symbols without using -fPIC is
>>>>> similar to the problem mentioned in
>>>>> https://bugs.llvm.org/show_bug.cgi?id=32425 .
>>>>>
>>>>> However I am not particularly bothered at this stage about having to use
>>>>> -fPIC. That would be fine.
>>>>>
>>>>> What I am struggling with is that having to use -fPIC is in conflict with
>>>>> the arm backend issue that creates bad relocations when building clang with
>>>>> -fPIC as mentioned in http://llvm.org/docs/HowToCrossCompileLLVM.html and so
>>>>> the build with -fPIC fails when building the clang binary.
>>>>>
>>>>> Regarding https://bugs.llvm.org/show_bug.cgi?id=32425 , please notice that
>>>>> contrary to what is reported there I definitely can build and execute a C
>>>>> hello world program without having to use -fPIC.
>>>>>
>>>>> It is only some symbols from musl that cannot be preempted by lld, not all
>>>>> of them.
>>>>>
>>>>> Unfortunately, when building llvm+clang+lld quite a few of those symbols are
>>>>> explicitly looked for by cmake and not found unless I use -fPIC.
>>>>>
>>>>> If I go ahead and build without using -fPIC then the build fails because it
>>>>> cannot preempt those symbols.
>>>>>
>>>>> It looks like a paradox to me and I think the solution would be to fix the
>>>>> fact that the arm backend does not like -fPIC as mentioned in
>>>>> http://llvm.org/docs/HowToCrossCompileLLVM.html . While it is probably
>>>>> correct that lld says it cannot preempt protected symbols, the arm backend
>>>>> issue is a known issue.
>>>>>
>>>>>
>>>>>>
>>>>>> Then I tried to use this compiler ( both the cross compiler and the native
>>>>>> compiler ) to compile llvm + clang + lld ( I want to have the toolchain
>>>>>> built with itself, again without any GNU software involved ) but when
>>>>>> building the clang executable I ran into the arm relocation problems
>>>>>> mentioned here in the “Hacks” section when using -fPIC:
>>>>>> http://llvm.org/docs/HowToCrossCompileLLVM.html .
>>>>>> On the other hand, I seem to need -fPIC otherwise cmake fails to find some
>>>>>> libc functions such as futimes/futimens and many others. If I use -fPIC for
>>>>>> CFLAGS but not for CXXFLAGS then cmake finds those symbols but then
>>>>>> obviously fails at a later stage with lld unable to preempt those symbols.
>>>>>>
>>>>>> This seems to be a conflict I cannot solve without someone within the llvm
>>>>>> team fixing the arm relocation problem. Is there any estimate of when this
>>>>>> could happen? I am happy to spend the time testing any solutions by building
>>>>>> my own toolchain until it succeeds. Or is there any other solution?
>>>>>>
>>>>>> Thank you,
>>>>>> Alex
>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> LLVM Developers mailing list
>>>>>> llvm-dev at lists.llvm.org
>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> LLVM Developers mailing list
>>>>> llvm-dev at lists.llvm.org
>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>
>>>
>

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