[llvm-dev] are the LLD libraries thread safe?

James Henderson via llvm-dev llvm-dev at lists.llvm.org
Wed Jul 25 02:11:42 PDT 2018 

Hi Andrew,

LLD relies on various bits of global state which are manipulated during the
link, so I wouldn't expect it to be thread safe at that level, although it
does attempt to reset that global state at the start of each call to
link(), so it should be callable sequentially.

Regards,

James

On 25 July 2018 at 02:37, Andrew Kelley via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Follow-up -
>
> Putting a global lock on running LLD indeed solved the issue, so I'm
> guessing that the LLD libraries do not in fact support being called from
> multiple threads simultaneously.
>
>
> On Tue, Jul 24, 2018 at 9:10 PM, Andrew Kelley <superjoe30 at gmail.com>
> wrote:
>
>> E.g. Is it intended to be allowed to call lld::elf::link in 2 different
>> threads at the same time?
>>
>> Follows is an example Valgrind error I ran into when doing the above.
>>
>> I'll try putting a global resource lock on invoking LLD and see if it
>> solves the problem.
>>
>> ==5467== Invalid write of size 8
>> ==5467==    at 0x525509: llvm::DenseMapBase<llvm::DenseMap<llvm::CachedHashStringRef,
>> int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int> >,
>> llvm::CachedHashStringRef, int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::moveFromOldBuckets(llvm::detail::DenseMapPair<llvm::CachedHashStringRef,
>> int>*, llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>*)
>> (DenseMap.h:375)
>> ==5467==    by 0x524C7F: llvm::DenseMap<llvm::CachedHashStringRef, int,
>> llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::grow(unsigned int) (DenseMap.h:739)
>> ==5467==    by 0x524077: llvm::DenseMapBase<llvm::DenseMap<llvm::CachedHashStringRef,
>> int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int> >,
>> llvm::CachedHashStringRef, int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::grow(unsigned int) (DenseMap.h:502)
>> ==5467==    by 0x522E54: llvm::detail::DenseMapPair<llvm::CachedHashStringRef,
>> int>* llvm::DenseMapBase<llvm::DenseMap<llvm::CachedHashStringRef, int,
>> llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int> >,
>> llvm::CachedHashStringRef, int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::InsertIntoBucketImpl<llvm::CachedHashStringRef>(llvm::CachedHashStringRef
>> const&, llvm::CachedHashStringRef const&, llvm::detail::DenseMapPair<llvm::CachedHashStringRef,
>> int>*) (DenseMap.h:546)
>> ==5467==    by 0x521258: llvm::detail::DenseMapPair<llvm::CachedHashStringRef,
>> int>* llvm::DenseMapBase<llvm::DenseMap<llvm::CachedHashStringRef, int,
>> llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int> >,
>> llvm::CachedHashStringRef, int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::InsertIntoBucket<llvm::CachedHashStringRef,
>> int>(llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>*,
>> llvm::CachedHashStringRef&&, int&&) (DenseMap.h:512)
>> ==5467==    by 0x51DEC9: std::pair<llvm::DenseMapIterator<llvm::CachedHashStringRef,
>> int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>, false>,
>> bool> llvm::DenseMapBase<llvm::DenseMap<llvm::CachedHashStringRef, int,
>> llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int> >,
>> llvm::CachedHashStringRef, int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::try_emplace<int>(llvm::CachedHashStringRef&&, int&&) (DenseMap.h:215)
>> ==5467==    by 0x51C52F: llvm::DenseMapBase<llvm::DenseMap<llvm::CachedHashStringRef,
>> int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int> >,
>> llvm::CachedHashStringRef, int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::insert(std::pair<llvm::CachedHashStringRef, int>&&) (DenseMap.h:199)
>> ==5467==    by 0x516836: lld::elf::SymbolTable::insert(llvm::StringRef)
>> (SymbolTable.cpp:225)
>> ==5467==    by 0x516A21: lld::elf::SymbolTable::insert(llvm::StringRef,
>> unsigned char, unsigned char, bool, lld::elf::InputFile*)
>> (SymbolTable.cpp:260)
>> ==5467==    by 0x51B88C: void lld::elf::SymbolTable::addShar
>> ed<llvm::object::ELFType<(llvm::support::endianness)1, true>
>> >(llvm::StringRef, lld::elf::SharedFile<llvm::obj
>> ect::ELFType<(llvm::support::endianness)1, true> >&,
>> llvm::object::ELFType<(llvm::support::endianness)1, true>::Sym const&,
>> unsigned int, unsigned int) (SymbolTable.cpp:483)
>> ==5467==    by 0x4E762A: lld::elf::SharedFile<llvm::obj
>> ect::ELFType<(llvm::support::endianness)1, true> >::parseRest()
>> (InputFiles.cpp:895)
>> ==5467==    by 0x51F69F: void lld::elf::SymbolTable::addFile
>> <llvm::object::ELFType<(llvm::support::endianness)1, true>
>> >(lld::elf::InputFile*) (SymbolTable.cpp:99)
>> ==5467==  Address 0xc6c7e80 is 53,568 bytes inside a block of size 98,304
>> free'd
>> ==5467==    at 0x4C2E26B: operator delete(void*) (in
>> /nix/store/j7sf6f2i9gws7c5mn8jyi8wc08ab1zbp-valgrind-3.13.0/
>> lib/valgrind/vgpreload_memcheck-amd64-linux.so)
>> ==5467==    by 0x4C714C: llvm::DenseMap<llvm::CachedHashStringRef, int,
>> llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::~DenseMap() (DenseMap.h:681)
>> ==5467==    by 0x4C9C7B: lld::elf::SymbolTable::~SymbolTable()
>> (SymbolTable.h:36)
>> ==5467==    by 0x4C9BF1: llvm::SpecificBumpPtrAllocator
>> <lld::elf::SymbolTable>::DestroyAll()::{lambda(char*,
>> char*)#1}::operator()(char*, char*) const (Allocator.h:410)
>> ==5467==    by 0x4C9D77: llvm::SpecificBumpPtrAllocator
>> <lld::elf::SymbolTable>::DestroyAll() (Allocator.h:421)
>> ==5467==    by 0x4D218F: lld::SpecificAlloc<lld::elf::SymbolTable>::reset()
>> (Memory.h:47)
>> ==5467==    by 0x3EF68B: lld::freeArena() (Memory.cpp:21)
>> ==5467==    by 0x4B3D41: lld::elf::link(llvm::ArrayRef<char const*>,
>> bool, llvm::raw_ostream&) (Driver.cpp:101)
>> ==5467==    by 0x39FC06: ZigLLDLink (zig_llvm.cpp:840)
>> ==5467==    by 0x38DE74: link.resume (link.zig:84)
>> ==5467==    by 0x2475EB: Loop_workerRun (loop.zig:511)
>> ==5467==    by 0x2495EC: MainFuncs_posixThreadMain (index.zig:2680)
>> ==5467==  Block was alloc'd at
>> ==5467==    at 0x4C2D1AF: operator new(unsigned long) (in
>> /nix/store/j7sf6f2i9gws7c5mn8jyi8wc08ab1zbp-valgrind-3.13.0/
>> lib/valgrind/vgpreload_memcheck-amd64-linux.so)
>> ==5467==    by 0x4CD027: llvm::DenseMap<llvm::CachedHashStringRef, int,
>> llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::allocateBuckets(unsigned int) (DenseMap.h:794)
>> ==5467==    by 0x524C18: llvm::DenseMap<llvm::CachedHashStringRef, int,
>> llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::grow(unsigned int) (DenseMap.h:732)
>> ==5467==    by 0x524077: llvm::DenseMapBase<llvm::DenseMap<llvm::CachedHashStringRef,
>> int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int> >,
>> llvm::CachedHashStringRef, int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::grow(unsigned int) (DenseMap.h:502)
>> ==5467==    by 0x522E54: llvm::detail::DenseMapPair<llvm::CachedHashStringRef,
>> int>* llvm::DenseMapBase<llvm::DenseMap<llvm::CachedHashStringRef, int,
>> llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int> >,
>> llvm::CachedHashStringRef, int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::InsertIntoBucketImpl<llvm::CachedHashStringRef>(llvm::CachedHashStringRef
>> const&, llvm::CachedHashStringRef const&, llvm::detail::DenseMapPair<llvm::CachedHashStringRef,
>> int>*) (DenseMap.h:546)
>> ==5467==    by 0x521258: llvm::detail::DenseMapPair<llvm::CachedHashStringRef,
>> int>* llvm::DenseMapBase<llvm::DenseMap<llvm::CachedHashStringRef, int,
>> llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int> >,
>> llvm::CachedHashStringRef, int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::InsertIntoBucket<llvm::CachedHashStringRef,
>> int>(llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>*,
>> llvm::CachedHashStringRef&&, int&&) (DenseMap.h:512)
>> ==5467==    by 0x51DEC9: std::pair<llvm::DenseMapIterator<llvm::CachedHashStringRef,
>> int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>, false>,
>> bool> llvm::DenseMapBase<llvm::DenseMap<llvm::CachedHashStringRef, int,
>> llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int> >,
>> llvm::CachedHashStringRef, int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::try_emplace<int>(llvm::CachedHashStringRef&&, int&&) (DenseMap.h:215)
>> ==5467==    by 0x51C52F: llvm::DenseMapBase<llvm::DenseMap<llvm::CachedHashStringRef,
>> int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int> >,
>> llvm::CachedHashStringRef, int, llvm::DenseMapInfo<llvm::CachedHashStringRef>,
>> llvm::detail::DenseMapPair<llvm::CachedHashStringRef, int>
>> >::insert(std::pair<llvm::CachedHashStringRef, int>&&) (DenseMap.h:199)
>> ==5467==    by 0x516836: lld::elf::SymbolTable::insert(llvm::StringRef)
>> (SymbolTable.cpp:225)
>> ==5467==    by 0x516A21: lld::elf::SymbolTable::insert(llvm::StringRef,
>> unsigned char, unsigned char, bool, lld::elf::InputFile*)
>> (SymbolTable.cpp:260)
>> ==5467==    by 0x51B88C: void lld::elf::SymbolTable::addShar
>> ed<llvm::object::ELFType<(llvm::support::endianness)1, true>
>> >(llvm::StringRef, lld::elf::SharedFile<llvm::obj
>> ect::ELFType<(llvm::support::endianness)1, true> >&,
>> llvm::object::ELFType<(llvm::support::endianness)1, true>::Sym const&,
>> unsigned int, unsigned int) (SymbolTable.cpp:483)
>> ==5467==    by 0x4E762A: lld::elf::SharedFile<llvm::obj
>> ect::ELFType<(llvm::support::endianness)1, true> >::parseRest()
>> (InputFiles.cpp:895)
>>
>>
>
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