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

Alessandro Pistocchi via llvm-dev llvm-dev at lists.llvm.org
Wed Jun 28 09:53:40 PDT 2017 

Cool thanks I'll give it a go :-)

Sent from my iPhone

> On 28 Jun 2017, at 18:36, Peter Smith <peter.smith at linaro.org> wrote:
> 
> 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 .
>>>> [  0%] Built target LLVMDemangle
>>>> [  3%] Built target LLVMSupport
>>>> [  3%] Built target LLVMTableGen
>>>> [  4%] Built target obj.llvm-tblgen
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>>>> [  4%] Built target intrinsics_gen
>>>> [  6%] Built target LLVMCore
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>>>> [ 44%] Built target ARMCommonTableGen
>>>> [ 45%] Built target LLVMARMCodeGen
>>>> [ 45%] Built target LLVMARMInfo
>>>> [ 45%] Built target LLVMARMAsmParser
>>>> [ 45%] Built target LLVMARMDisassembler
>>>> [ 45%] Built target LLVMARMAsmPrinter
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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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