[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
Mon Jul 3 05:45:51 PDT 2017
Sent from my iPhone
> On 3 Jul 2017, at 10:51, Peter Smith <peter.smith at linaro.org> wrote:
>
> Hello Alessandro,
>
> That particular error message occurs when a dynamic relocation would
> need to be created in the read-only part of the shared library. This
> is usually indicative that some part of libobjc2 hasn't been compiled
> with -fpic or contains some assembly that is making a direct reference
> to a label address rather than accessing it relative to the .got.
That is precisely what happened: an asm file referencing a C symbol's absolute address.
I changed the asm file so that it references the symbol relative to the pc.
Thanks for help :-)
A
>
> There is an option -ztext (lld defaults to -znotext) that permits
> these relocations. It maybe that if libobjc2 can be linked with other
> linkers -ztext is the default, you should be able to find out if this
> is the case by looking at the dynamic section with readelf -d and
> looking for DF_TEXTREL or DT_TEXTREL.
>
> Assuming lld is behaving correctly, in general it is better to find
> and fix the source file that is generating these relocations as having
> dynamic relocations in the read-only segment is not ideal. I suggest
> finding the object that contains the R_ARM_ABS32 and tracing it back
> from the object file to the source file and seeing what has generated
> it. I usually use objdump -r -d for this purpose.
>
> Hope that helps
>
> Peter
>
>> On 1 July 2017 at 13:34, Alessandro Pistocchi <apukfreelance at gmail.com> wrote:
>> Hi, I managed to build both the cross compiler and the native compiler with led.
>>
>> Now I am getting a "can't create dynamic relocation R_ARM_ABS32" error when building libobjc2 from gnustep and linking with lld.
>>
>> Any clues?
>>
>> Sent from my iPhone
>>
>>> On 30 Jun 2017, at 10:28, Peter Smith <peter.smith at linaro.org> wrote:
>>>
>>> At a guess that looks like your llvm and lld checkouts are not quite
>>> in synch. It will be worth updating llvm and lld to top of trunk.
>>>
>>> I've rebased the consolidated patch https://reviews.llvm.org/D34634
>>> this morning, it might be worth trying that if you are seeing
>>> problems.
>>>
>>> Peter
>>>
>>>> On 29 June 2017 at 22:09, Alessandro Pistocchi <apukfreelance at gmail.com> wrote:
>>>> Hi, I tried patching and rebuilding and now I get this error. Did I miss anything?
>>>>
>>>> /home/yawmoo/Desktop/clfs/sources/llvm/tools/lld/ELF/InputFiles.cpp:82:23: error:
>>>> no matching constructor for initialization of 'llvm::DWARFDebugLine'
>>>> DwarfLine.reset(new DWARFDebugLine(&Dwarf.getLineSection().Relocs));
>>>> ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>> /home/yawmoo/Desktop/clfs/sources/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h:27:7: note:
>>>> candidate constructor (the implicit move constructor) not viable: no known
>>>> conversion from 'const RelocAddrMap *' (aka 'const DenseMap<unsigned long,
>>>> llvm::RelocAddrEntry> *') to 'llvm::DWARFDebugLine' for 1st argument
>>>> class DWARFDebugLine {
>>>> ^
>>>> /home/yawmoo/Desktop/clfs/sources/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h:27:7: note:
>>>> candidate constructor (the implicit copy constructor) not viable: no known
>>>> conversion from 'const RelocAddrMap *' (aka 'const DenseMap<unsigned long,
>>>> llvm::RelocAddrEntry> *') to 'const llvm::DWARFDebugLine' for 1st argument
>>>> /home/yawmoo/Desktop/clfs/sources/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h:27:7: note:
>>>> candidate constructor (the implicit default constructor) not viable:
>>>> requires 0 arguments, but 1 was provided
>>>> /home/yawmoo/Desktop/clfs/sources/llvm/tools/lld/ELF/InputFiles.cpp:89:34: error:
>>>> no viable conversion from 'llvm::DataExtractor' to 'const
>>>> llvm::DWARFDataExtractor'
>>>> DwarfLine->getOrParseLineTable(LineData, 0);
>>>> ^~~~~~~~
>>>> /home/yawmoo/Desktop/clfs/sources/llvm/include/llvm/DebugInfo/DWARF/DWARFDataExtractor.h:20:7: note:
>>>> candidate constructor (the implicit copy constructor) not viable: cannot
>>>> bind base class object of type 'llvm::DataExtractor' to derived class
>>>> reference 'const llvm::DWARFDataExtractor &' for 1st argument
>>>> class DWARFDataExtractor : public DataExtractor {
>>>> ^
>>>> /home/yawmoo/Desktop/clfs/sources/llvm/include/llvm/DebugInfo/DWARF/DWARFDataExtractor.h:20:7: note:
>>>> candidate constructor (the implicit move constructor) not viable: cannot
>>>> bind base class object of type 'llvm::DataExtractor' to derived class
>>>> reference 'llvm::DWARFDataExtractor &&' for 1st argument
>>>> /home/yawmoo/Desktop/clfs/sources/llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLine.h:237:66: note:
>>>> passing argument to parameter 'DebugLineData' here
>>>> const LineTable *getOrParseLineTable(const DWARFDataExtractor &DebugLineData,
>>>> ^
>>>> 2 errors generated.
>>>> tools/lld/ELF/CMakeFiles/lldELF.dir/build.make:494: recipe for target 'tools/lld/ELF/CMakeFiles/lldELF.dir/InputFiles.cpp.o' failed
>>>> make[2]: *** [tools/lld/ELF/CMakeFiles/lldELF.dir/InputFiles.cpp.o] Error 1
>>>> CMakeFiles/Makefile2:49925: recipe for target 'tools/lld/ELF/CMakeFiles/lldELF.dir/all' failed
>>>> make[1]: *** [tools/lld/ELF/CMakeFiles/lldELF.dir/all] Error 2
>>>> Makefile:149: recipe for target 'all' failed
>>>> make: *** [all] Error 2
>>>>
>>>>
>>>>> On 28 Jun 2017, at 19:04, Shoaib Meenai <smeenai at fb.com> wrote:
>>>>>
>>>>> The bottom of the bug has the revision numbers (e.g. D34035). That one
>>>>> corresponds to e.g. https://reviews.llvm.org/D34035
>>>>>
>>>>> There's also https://reviews.llvm.org/D34634 which contains all of Peter's
>>>>> patches, but it's not going to rebase cleanly once the individual patches
>>>>> start going in.
>>>>>
>>>>> On 6/28/17, 10:56 AM, "Alessandro Pistocchi" <apukfreelance at gmail.com> wrote:
>>>>>
>>>>> Sorry for the noob question: where do I get the patches?
>>>>>
>>>>> I can see the bug but not a link to the patches ( I don't have a login if that is the issue )
>>>>>
>>>>> Sent from my iPhone
>>>>>
>>>>>> On 28 Jun 2017, at 19:36, Shoaib Meenai <smeenai at fb.com> wrote:
>>>>>>
>>>>>> I've successfully used Peter's patches to get past those relocation errors.
>>>>>>
>>>>>> On 6/28/17, 9:36 AM, "llvm-dev on behalf of Peter Smith via llvm-dev" <llvm-dev-bounces at lists.llvm.org on behalf of llvm-dev at lists.llvm.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://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.llvm.org_show-5Fbug.cgi-3Fid-3D33612&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=MoG8NHuM6pLu1J1B-yHnV-uqDvXgdp72ydIhDlNyQ9Q&s=RpqKAJtCInfokC4ejkvv1e1hbMx22g7c6-v8JNuzOrY&e= 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
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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://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.llvm.org_show-5Fbug.cgi-3Fid-3D32425-3F&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=MoG8NHuM6pLu1J1B-yHnV-uqDvXgdp72ydIhDlNyQ9Q&s=NukMRJ9yTsw5j3ENYmb5P6xnVjqZDGr_RtEBf88y-aI&e=
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> 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://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.llvm.org_show-5Fbug.cgi-3Fid-3D32425&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=MoG8NHuM6pLu1J1B-yHnV-uqDvXgdp72ydIhDlNyQ9Q&s=9sykAqiCyyRAxvbFBkT7xc41tFV4gbqVNlLPtuZwgEo&e= .
>>>>>>>>>>>
>>>>>>>>>>> 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 https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_docs_HowToCrossCompileLLVM.html&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=MoG8NHuM6pLu1J1B-yHnV-uqDvXgdp72ydIhDlNyQ9Q&s=ZDjTpKgbVvk-6KPfK36_iXsQkmN0tZo-GFLmojAfWdI&e= and so
>>>>>>>>>>> the build with -fPIC fails when building the clang binary.
>>>>>>>>>>>
>>>>>>>>>>> Regarding https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.llvm.org_show-5Fbug.cgi-3Fid-3D32425&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=MoG8NHuM6pLu1J1B-yHnV-uqDvXgdp72ydIhDlNyQ9Q&s=9sykAqiCyyRAxvbFBkT7xc41tFV4gbqVNlLPtuZwgEo&e= , 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
>>>>>>>>>>> https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_docs_HowToCrossCompileLLVM.html&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=MoG8NHuM6pLu1J1B-yHnV-uqDvXgdp72ydIhDlNyQ9Q&s=ZDjTpKgbVvk-6KPfK36_iXsQkmN0tZo-GFLmojAfWdI&e= . 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:
>>>>>>>>>>>> https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_docs_HowToCrossCompileLLVM.html&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=MoG8NHuM6pLu1J1B-yHnV-uqDvXgdp72ydIhDlNyQ9Q&s=ZDjTpKgbVvk-6KPfK36_iXsQkmN0tZo-GFLmojAfWdI&e= .
>>>>>>>>>>>> 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
>>>>>>>>>>>> https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.llvm.org_cgi-2Dbin_mailman_listinfo_llvm-2Ddev&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=MoG8NHuM6pLu1J1B-yHnV-uqDvXgdp72ydIhDlNyQ9Q&s=elMtK81LIlpU0bdvd9Zwk2UtgI9He36ddrHDrVDKt94&e=
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> _______________________________________________
>>>>>>>>>>> LLVM Developers mailing list
>>>>>>>>>>> llvm-dev at lists.llvm.org
>>>>>>>>>>> https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.llvm.org_cgi-2Dbin_mailman_listinfo_llvm-2Ddev&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=MoG8NHuM6pLu1J1B-yHnV-uqDvXgdp72ydIhDlNyQ9Q&s=elMtK81LIlpU0bdvd9Zwk2UtgI9He36ddrHDrVDKt94&e=
>>>>>>>>>>>
>>>>>>>>>
>>>>>>>
>>>>>> _______________________________________________
>>>>>> LLVM Developers mailing list
>>>>>> llvm-dev at lists.llvm.org
>>>>>> https://urldefense.proofpoint.com/v2/url?u=http-3A__lists.llvm.org_cgi-2Dbin_mailman_listinfo_llvm-2Ddev&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=MoG8NHuM6pLu1J1B-yHnV-uqDvXgdp72ydIhDlNyQ9Q&s=elMtK81LIlpU0bdvd9Zwk2UtgI9He36ddrHDrVDKt94&e=
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
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