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

Dave Bozier via llvm-dev llvm-dev at lists.llvm.org
Wed Jul 25 04:08:33 PDT 2018 

Are there any plans to make LLD thread safe in the future? This would be a
useful feature for us.

Cheers,

Dave

On Wed, Jul 25, 2018 at 10:12 AM James Henderson via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> 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::addShared<llvm::object::ELFType<(llvm::support::endianness)1,
>>> true> >(llvm::StringRef,
>>> lld::elf::SharedFile<llvm::object::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::object::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::addShared<llvm::object::ELFType<(llvm::support::endianness)1,
>>> true> >(llvm::StringRef,
>>> lld::elf::SharedFile<llvm::object::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::object::ELFType<(llvm::support::endianness)1,
>>> true> >::parseRest() (InputFiles.cpp:895)
>>>
>>>
>>
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>>
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