[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 09:09:24 PDT 2017 

> 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
[  4%] Built target llvm-tblgen
[  4%] Built target AttributeCompatFuncTableGen
[  4%] Built target intrinsics_gen
[  6%] Built target LLVMCore
[  6%] Built target LLVMIRReader
[ 13%] Built target LLVMCodeGen
[ 14%] Built target LLVMSelectionDAG
[ 14%] Built target LLVMAsmPrinter
[ 14%] Built target LLVMMIRParser
[ 14%] Built target LLVMGlobalISel
[ 14%] Built target LLVMBinaryFormat
[ 14%] Built target LLVMBitReader
[ 16%] Built target LLVMBitWriter
[ 18%] Built target LLVMTransformUtils
[ 19%] Built target LLVMInstrumentation
[ 19%] Built target LLVMInstCombine
[ 22%] Built target LLVMScalarOpts
[ 22%] Built target LLVMipo
[ 24%] Built target LLVMVectorize
[ 24%] Built target LLVMHello_exports
[ 24%] Built target LLVMHello
[ 26%] Built target LLVMObjCARCOpts
[ 26%] Built target LLVMCoroutines
[ 26%] Built target LLVMLinker
[ 29%] Built target LLVMAnalysis
[ 29%] Built target llvm_vcsrevision_h
[ 29%] Built target LLVMLTO
[ 32%] Built target LLVMMC
[ 32%] Built target LLVMMCParser
[ 32%] Built target LLVMMCDisassembler
[ 32%] Built target LLVMObject
[ 32%] Built target LLVMObjectYAML
[ 34%] Built target LLVMOption
[ 36%] Built target LLVMDebugInfoDWARF
[ 36%] Built target LLVMDebugInfoMSF
[ 37%] Built target LLVMDebugInfoCodeView
[ 40%] Built target LLVMDebugInfoPDB
[ 42%] Built target LLVMSymbolize
[ 42%] Built target LLVMExecutionEngine
[ 42%] Built target LLVMInterpreter
[ 42%] Built target LLVMMCJIT
[ 42%] Built target LLVMOrcJIT
[ 42%] Built target LLVMRuntimeDyld
[ 42%] Built target LLVMTarget
[ 44%] Built target ARMCommonTableGen
[ 45%] Built target LLVMARMCodeGen
[ 45%] Built target LLVMARMInfo
[ 45%] Built target LLVMARMAsmParser
[ 45%] Built target LLVMARMDisassembler
[ 45%] Built target LLVMARMAsmPrinter
[ 45%] Built target LLVMARMDesc
[ 47%] Built target LLVMAsmParser
[ 47%] Built target LLVMLineEditor
[ 47%] Built target LLVMProfileData
[ 47%] Built target LLVMCoverage
[ 49%] Built target LLVMFuzzerNoMainObjects
[ 49%] Built target LLVMFuzzerNoMain
[ 49%] Built target LLVMFuzzer
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[ 49%] Built target LibOptionsTableGen
[ 49%] Built target LLVMLibDriver
[ 49%] Built target LLVMXRay
[ 49%] Built target gtest
[ 49%] Built target LLVMTestingSupport
[ 49%] Built target FileCheck
[ 49%] Built target llvm-PerfectShuffle
[ 49%] Built target count
[ 49%] Built target not
[ 49%] Built target yaml-bench
[ 49%] Built target LTO_exports
[ 50%] Built target LTO
[ 50%] Built target llvm-ar
[ 50%] Built target llvm-ranlib
[ 50%] Built target llvm-lib
[ 50%] Built target llvm-config
[ 50%] Built target llvm-lto
[ 50%] Built target llvm-profdata
[ 50%] Built target obj.clang-tblgen
[ 50%] Built target clang-tblgen
[ 55%] Built target clang-headers
[ 55%] Built target ClangSACheckers
[ 55%] Built target ClangCommentCommandList
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[ 55%] Built target ClangAttrDump
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[ 55%] Built target ClangCommentNodes
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[ 55%] Built target ClangDiagnosticIndexName
[ 55%] Built target ClangDiagnosticSerialization
[ 55%] Built target ClangDiagnosticAnalysis
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[ 57%] Built target ClangDiagnosticFrontend
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[ 57%] Built target ClangDiagnosticCommon
[ 57%] Built target ClangAttrSubjectMatchRuleList
[ 57%] Built target ClangARMNeon
[ 59%] Built target ClangAttrParserStringSwitches
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[ 59%] Built target ClangAttrParsedAttrKinds
[ 59%] Built target ClangAttrSpellingListIndex
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[ 59%] Built target ClangAttrParsedAttrImpl
[ 59%] Built target ClangAttrTemplateInstantiate
[ 59%] Built target ClangAttrPCHRead
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[ 60%] Built target clangBasic
[ 62%] Built target clangLex
[ 62%] Built target clangParse
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[ 63%] Built target clangASTMatchers
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[ 68%] Built target clangAnalysis
[ 68%] Built target clangEdit
[ 70%] Built target clangRewrite
[ 72%] Built target clangARCMigrate
[ 72%] Built target ClangDriverOptions
[ 75%] Built target clangDriver
[ 75%] Built target clangSerialization
[ 77%] Built target clangFrontend
[ 77%] Built target clangRewriteFrontend
[ 77%] Built target clangFrontendTool
[ 77%] Built target clangTooling
[ 77%] Built target clangToolingCore
[ 77%] Built target clangToolingRefactor
[ 77%] Built target clangIndex
[ 78%] Built target clangStaticAnalyzerCore
[ 83%] Built target clangStaticAnalyzerCheckers
[ 83%] Built target clangStaticAnalyzerFrontend
[ 83%] Built target clangFormat
[ 85%] Built target diagtool
[ 85%] Built target clang-offload-bundler
[ 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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