[llvm-dev] [DebugInfo] DWARF C API

Thu Apr 25 02:57:36 PDT 2019

Wow I figured it out. Thanks for your input David :)

Son Tuan Vu

On Thu, Apr 25, 2019 at 3:17 AM David Blaikie <dblaikie at gmail.com> wrote:

> Sounds to me like the DWARFContext might not have a valid
> reference/pointer/whatever to the ObjectFile? Is there a chance the
> ObjectFile pointer in the DWARFContext is null?
>
> I'd suggest you poke around in a debugger there to check what state
> it's in in a good (non-C-wrapped) example and in the C-wrapped example
> to compare/contrast.
>
> On Wed, Apr 24, 2019 at 2:54 PM Son Tuan VU <sontuan.vu119 at gmail.com>
> wrote:
> >
> > Hi David,
> >
> > Sorry, I forget to attach the valgrind dump to this. I was not sure if
> my implementation was ok, so I wanted to ask if I've done something wrong
> first.
> >
> >  Process terminating with default action of signal 11 (SIGSEGV)
> >  Access not within mapped region at address 0xB
> >    at 0x54F4516:
> llvm::object::COFFObjectFile::moveSectionNext(llvm::object::DataRefImpl&)
> const (COFFObjectFile.cpp:267)
> >     by 0x55A62FB:
> llvm::object::ObjectFile::isBerkeleyText(llvm::object::DataRefImpl) const
> (ObjectFile.cpp:80)
> >     by 0x5538CF9: llvm::object::RelocationRef::getType() const
> (ObjectFile.h:543)
> >     by 0x55AE53E: llvm::object::resolveARM(llvm::object::RelocationRef,
> unsigned long, unsigned long) (RelocationResolver.cpp:250)
> >     by 0x502802B: llvm::DWARFDataExtractor::getRelocatedValue(unsigned
> int, unsigned int*, unsigned long*) const (DWARFDataExtractor.cpp:27)
> >     by 0x5071C2F: llvm::DWARFUnitHeader::extract(llvm::DWARFContext&,
> llvm::DWARFDataExtractor const&, unsigned int*, llvm::DWARFSectionKind,
> llvm::DWARFUnitIndex const*, llvm::DWARFUnitIndex::Entr    y const*)
> (DWARFUnit.cpp:254)
> >     by 0x5070BAD:
> llvm::DWARFUnitVector::addUnitsImpl(llvm::DWARFContext&, llvm::DWARFObject
> const&, llvm::DWARFSection const&, llvm::DWARFDebugAbbrev const*,
> llvm::DWARFSection const*, llvm::DWARF    Section const*, llvm::StringRef,
> llvm::DWARFSection const&, llvm::DWARFSection const*, llvm::DWARFSection
> const&, bool, bool, bool, llvm::DWARFSectionKind)::{lambda(unsigned int,
> llvm::DWARFSectionKind, llvm    ::DWARFSection const*,
> llvm::DWARFUnitIndex::Entry const*)#1}::operator()(unsigned int,
> llvm::DWARFSectionKind, llvm::DWARFSection const*,
> llvm::DWARFUnitIndex::Entry const*) const (DWARFUnit.cpp:82)
> >
> >     by 0x50751E1:
> std::_Function_handler<std::unique_ptr<llvm::DWARFUnit,
> std::default_delete<llvm::DWARFUnit> > (unsigned int,
> llvm::DWARFSectionKind, llvm::DWARFSection const*, llvm::DWARFUnitInd
> ex::Entry const*), llvm::DWARFUnitVector::addUnitsImpl(llvm::DWARFContext&,
> llvm::DWARFObject const&, llvm::DWARFSection const&, llvm::DWARFDebugAbbrev
> const*, llvm::DWARFSection const*, llvm::DWARFSection c    onst*,
> llvm::StringRef, llvm::DWARFSection const&, llvm::DWARFSection const*,
> llvm::DWARFSection const&, bool, bool, bool,
> llvm::DWARFSectionKind)::{lambda(unsigned int, llvm::DWARFSectionKind,
> llvm::DWARFSe    ction const*, llvm::DWARFUnitIndex::Entry
> const*)#1}>::_M_invoke(std::_Any_data const&, unsigned int,
> llvm::DWARFSectionKind, llvm::DWARFSection const*,
> llvm::DWARFUnitIndex::Entry const*) (functional:2057)
> >
> >     by 0x507656E: std::function<std::unique_ptr<llvm::DWARFUnit,
> std::default_delete<llvm::DWARFUnit> > (unsigned int,
> llvm::DWARFSectionKind, llvm::DWARFSection const*,
> llvm::DWARFUnitIndex::Entry     const*)>::operator()(unsigned int,
> llvm::DWARFSectionKind, llvm::DWARFSection const*,
> llvm::DWARFUnitIndex::Entry const*) const (functional:2471)
> >
> >     by 0x5070FE6:
> llvm::DWARFUnitVector::addUnitsImpl(llvm::DWARFContext&, llvm::DWARFObject
> const&, llvm::DWARFSection const&, llvm::DWARFDebugAbbrev const*,
> llvm::DWARFSection const*, llvm::DWARF    Section const*, llvm::StringRef,
> llvm::DWARFSection const&, llvm::DWARFSection const*, llvm::DWARFSection
> const&, bool, bool, bool, llvm::DWARFSectionKind) (DWARFUnit.cpp:111)
> >
> >     by 0x50708CF:
> llvm::DWARFUnitVector::addUnitsForSection(llvm::DWARFContext&,
> llvm::DWARFSection const&, llvm::DWARFSectionKind) (DWARFUnit.cpp:44)
> >     by 0x5000AAE:
> llvm::DWARFContext::parseNormalUnits()::{lambda(llvm::DWARFSection
> const&)#1}::operator()(llvm::DWARFSection const&) const
> (DWARFContext.cpp:881)
> >
> > However, I can't see how this error can relate to the
> wrapping/unwrapping macros generating C structure?
> >
> > Thanks a lot for your time
> >
> > Son Tuan Vu
> >
> >
> > On Wed, Apr 24, 2019 at 11:03 PM David Blaikie <dblaikie at gmail.com>
> wrote:
> >>
> >> Might be worth running under valgrind or the LLVM sanitizers? (could
> >> help diagnose what's going wrong more specifically than a segfault)
> >>
> >> On Wed, Apr 24, 2019 at 1:57 PM Son Tuan VU via llvm-dev
> >> <llvm-dev at lists.llvm.org> wrote:
> >> >
> >> > Hi folks,
> >> >
> >> > I am trying to implement the C bindings API for
> DebugInfo::DWARF::DWARFDie. My goal is to have a C library that reads and
> parses DWARF debugging format (just like how llvm-dwarfdump does, but maybe
> more than just dumping debug info)
> >> >
> >> > I've started with creating C structure for
> DebugInfo::DWARF::DWARFContext which contains all DWARF DIEs in the object
> file. For this I used
> >> > ```
> >> > DEFINE_SIMPLE_CONVERSION_FUNCTIONS(DWARFContext, LLVMDWARFContextRef)
> >> > ```
> >> > then defined some C functions
> >> > ```
> >> > LLVMDWARFContextRef LLVMCreateDWARFContext(LLVMBinaryRef Bin) {
> >> >   std::unique_ptr<DWARFContext> DICtx =
> DWARFContext::create(*unwrap(Bin));
> >> >   return wrap(DICtx.release());
> >> > }
> >> >
> >> > void LLVMPrintDWARFContext(LLVMDWARFContextRef C) {
> >> >   DIDumpOptions DumpOpts;
> >> >   DumpOpts.DumpType = DIDT_DebugInfo; // I only care about the
> .debug_info section
> >> >   unwrap(C)->dump(outs(), DumpOpts);
> >> > }
> >> > ```
> >> > However, I got a segfault when trying to dump the LLVMDWARFContextRef
> using the second function. More precisely, it segfaulted when dumping the
> attribute of the DWARFDie.
> >> >
> >> > I tried to do this instead to see if the wrapping/unwrapping has bugs
> >> > ```
> >> > LLVMDWARFContextRef LLVMCreateDWARFContext(LLVMBinaryRef Bin) {
> >> >   std::unique_ptr<DWARFContext> DICtx =
> DWARFContext::create(*unwrap(Bin));
> >> >   LLVMDWARFContextRef C = wrap(DICtx.release());
> >> >   LLVMPrintDWARFContext(C);
> >> >   return C;
> >> > }
> >> > ```
> >> > and the call to LLVMPrintDWARFContext did not segfault this time.
> >> >
> >> > Can anybody who knows about DWARFContext and DWARFDie tell me what I
> did wrong? Or is it a bug in DWARFDie::dump() method?
> >> >
> >> > Thank you very much for your help,
> >> >
> >> > Son Tuan Vu
> >> > _______________________________________________
> >> > LLVM Developers mailing list
> >> > llvm-dev at lists.llvm.org
> >> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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