[llvm-dev] Possible stack corruption during call to JITSymbol::getAddress() (original) (raw)

Lang Hames via llvm-dev llvm-dev at lists.llvm.org
Thu Apr 13 10:53:02 PDT 2017

Hi David,

This is definitely the right place to ask.

Let me see if I can reproduce this locally...

Cheers, Lang.

On Sun, Apr 9, 2017 at 2:02 PM, David Lurton via llvm-dev < llvm-dev at lists.llvm.org> wrote:

Firstly, apologies if this is not the right place to be asking this question--feel free to point me in the correct direction. I could be doing something wrong here but stackoverflow didn't feel like the correct place for this since there's so little there about LLVM ORC.

Basically, I have a reproduction case (below) where if I throw an exception before I call JITSymbol::getAddress() everything works properly but throwing the same exception afterward will result in a SIGSEGV during stack unwinding. This suggests to me that somehow the stack is getting corrupted during the JITSymbol::getAddress() call. This problem was initially discovered while working on my own project. While troubleshooting this I've discvoered that when LLVM is -DLLVMUSESANITIZER:STRING=Address the problem happens at different points during execution, perhaps having something to do with the padding around the stack variables added by the sanitizer? See the note after the call to runTest() in main(). I'm running this under an up-to-date Antergos Linux, clang version: 3.9.1 (tried compiling LLVM and the example program below with gcc 6.3.1 and the result is the same) clang set to default compiler by setting the following environment variables: CC=/usr/bin/clang CXX=/usr/bin/clang++ Commands used to build LLVM: git clone https://github.com/llvm-mirror/llvm.git git checkout release40 cd llvm mkdir build cd build cmake .. -DLLVMBUILDLLVMDYLIB:BOOL=ON -DLLVMENABLERTTI:BOOL=ON -DLLVMENABLEEH:BOOL=ON -DLLVMUSESANITIZER:STRING=Address -DLLVMPARALLELCOMPILEJOBS:STRING=8 -DLLVMENABLEASSERTIONS:BOOL=ON cmake --build . -- -j 8 sudo cmake --build . --target install Command used to build test case executable: clang test.cpp -std=c++14 -lstdc++ -lLLVM-4.0 -Wall -pedantic -Wextra -fstack-protector-all -fsanitize=address -fexceptions Then of course: ./a.out Output from the a.out: ASAN:DEADLYSIGNAL ================================================================= ==6582==ERROR: AddressSanitizer: SEGV on unknown address 0x7f59eeb06020 (pc 0x7f59f1b20930 bp 0x000000000001 sp 0x7ffc5e546218 T0) ==6582==The signal is caused by a READ memory access.

The result if running backtrace in GDB while execution is paused after the SIGSEGV occurs: #0 readencodedvaluewithbase (encoding=encoding at entry=28 '\034', base=base at entry=0, p=p at entry=0x7fffe8a06020 <error: Cannot access memory_ _at address 0x7fffe8a06020>, val=val at entry=0x7fffffffd6d8) at /build/gcc/src/gcc/libgcc/unwind-pe.h:252 #1 0x00007fffeba05a61 in binarysearchsingleencodingfdes (pc=0x7fffeba04426 <UnwindResume+54>, ob=0x0) at /build/gcc/src/gcc/libgcc/unwind-dw2-fde.c:908 #2 searchobject (ob=ob at entry=0x60400001d9d0, pc=pc at entry=0x7fffeba04426 <UnwindResume+54>) at /build/gcc/src/gcc/libgcc/unwind-dw2-fde.c:977 #3 0x00007fffeba05fdd in UnwindFindregisteredFDE (bases=0x7fffffffda78, pc=0x7fffeba04426 <UnwindResume+54>) at /build/gcc/src/gcc/libgcc/unwind-dw2-fde.c:1013 #4 UnwindFindFDE (pc=0x7fffeba04426 <UnwindResume+54>, bases=bases at entry=0x7fffffffda78) at /build/gcc/src/gcc/libgcc/ unwind-dw2-fde-dip.c:454 #5 0x00007fffeba02b23 in uwframestatefor (context=context at entry=0x7fffffffd9d0, fs=fs at entry=0x7fffffffd820) at /build/gcc/src/gcc/libgcc/unwind-dw2.c:1241 #6 0x00007fffeba03d40 in uwinitcontext1 (context=context at entry=0x7fffffffd9d0, outercfa=outercfa at entry=0x7fffffffdc00, outerra=0x5110fc) at /build/gcc/src/gcc/libgcc/unwind-dw2.c:1562 #7 0x00007fffeba04427 in UnwindResume (exc=0x60d00000c7b0) at /build/gcc/src/gcc/libgcc/unwind.inc:224 #8 0x00000000005110fc in runTest () at /home/dave/projects/untitled/ test.cpp:124 #9 0x0000000000511138 in main (argc=1, argv=0x7fffffffe698) at /home/dave/projects/untitled/test.cpp:132 My test-case is below. In runTest(), note the commented out throw statement before symbol.getAddress() and the uncommented one after it. Also note the comments after the call to runTest() in main(). Thanks. #include "llvm/ADT/STLExtras.h" #include "llvm/ExecutionEngine/ExecutionEngine.h" #include "llvm/IR/IRBuilder.h" #include "llvm/ExecutionEngine/SectionMemoryManager.h" #include "llvm/ExecutionEngine/Orc/CompileUtils.h" #include "llvm/ExecutionEngine/Orc/IRCompileLayer.h" #include "llvm/ExecutionEngine/Orc/LambdaResolver.h" #include "llvm/ExecutionEngine/Orc/ObjectLinkingLayer.h" #include "llvm/IR/Mangler.h" #include "llvm/Support/DynamicLibrary.h" #include "llvm/Support/TargetSelect.h" #include using namespace llvm; using namespace llvm::orc; /** This class taken verbatim from * https://github.com/llvm-mirror/llvm/blob/release40/ examples/Kaleidoscope/BuildingAJIT/Chapter1/KaleidoscopeJIT.h * This is from the same revision of LLVM I am using (the release40 branch as of 4/8/2017) */ class KaleidoscopeJIT { private: std::uniqueptr TM; const DataLayout DL; ObjectLinkingLayer<> ObjectLayer; IRCompileLayer<decltype(ObjectLayer)> CompileLayer; public: typedef decltype(CompileLayer)::ModuleSetHandleT ModuleHandle; KaleidoscopeJIT() : TM(EngineBuilder().selectTarget()), DL(TM->createDataLayout()), CompileLayer(ObjectLayer, SimpleCompiler(*TM)) { llvm::sys::DynamicLibrary::LoadLibraryPermanently(nullptr); } TargetMachine &getTargetMachine() { return *TM; } ModuleHandle addModule(std::uniqueptr M) { // Build our symbol resolver: // Lambda 1: Look back into the JIT itself to find symbols that are part of // the same "logical dylib". // Lambda 2: Search for external symbols in the host process. auto Resolver = createLambdaResolver( [&](const std::string &Name) { if (auto Sym = CompileLayer.findSymbol(Name, false)) return Sym; return JITSymbol(nullptr); }, [](const std::string &Name) { if (auto SymAddr = RTDyldMemoryManager:: getSymbolAddressInProcess(Name)) return JITSymbol(SymAddr, JITSymbolFlags::Exported); return JITSymbol(nullptr); }); // Build a singleton module set to hold our module. std::vector<std::uniqueptr> Ms; Ms.pushback(std::move(M)); // Add the set to the JIT with the resolver we created above and a newly // created SectionMemoryManager. return CompileLayer.addModuleSet(std::move(Ms), makeunique<_ _SectionMemoryManager>(), std::move(Resolver)); } JITSymbol findSymbol(const std::string Name) { std::string MangledName; rawstringostream MangledNameStream(MangledName); Mangler::getNameWithPrefix(MangledNameStream, Name, DL); return CompileLayer.findSymbol(MangledNameStream.str(), true); } void removeModule(ModuleHandle H) { CompileLayer.removeModuleSet(H); } }; const std::string FUNCNAME = "someFunction"; void runTest() { llvm::LLVMContext context; llvm::IRBuilder<> irBuilder{context}; KaleidoscopeJIT jit; auto module = std::makeuniquellvm::Module("help", context); module->setDataLayout(jit.getTargetMachine().createDataLayout()); auto function = llvm::castllvm::Function( module->getOrInsertFunction(FUNCNAME, llvm::Type::getInt32Ty(context), nullptr)); auto block = llvm::BasicBlock::Create(context, "functionBody", function); irBuilder.SetInsertPoint(block); irBuilder.CreateRet(llvm::ConstantInt::get(context, llvm::APInt(32, 1, true))); jit.addModule(std::move(module)); llvm::JITSymbol symbol = jit.findSymbol(FUNCNAME); //Just to ensure that the symbol is in fact valid (symbol evaluates to true during execution) if(!symbol) { throw std::runtimeerror("Symbol not found"); } //when uncommented, the throw statement does NOT cause a SIGSEGV. //throw std::runtimeerror("This should not crash."); uint64t ptr = symbol.getAddress(); //HOWEVER... a SIGSEGV occurs during stack-unwinding while throwing the exception below. //Hence, the call to symbol.getAddress() must be causing some kind of memory corruption. //My guess is that it's clobbering the stack. throw std::runtimeerror("This should not crash but does anyway."); std::cout << "Ptr is " << ptr << "\n";_ _int (*someFuncPtr)() = reinterpretcast<int (*)()>(ptr); //int (someFuncPtr)() = (int ()())ptr; int returnValue = someFuncPtr(); std::cout << "Return value is: " << returnValue << "\n"; } int main(int argc, char **argv) { llvm::InitializeNativeTarget(); llvm::InitializeAllAsmPrinters(); try { runTest(); //NOTE: if LLVM is compiled without -DLLVMUSESANITIZER:STRING=Address, the last throw in runTest() does not cause //a SIGSEGV, however this throw will. //throw std::runtimeerror("This should not crash but does anyway."); } catch(std::runtimeerror &e) { std::cout << "Exception caught: " << e.what() << "\n"; } llvm::llvmshutdown(); return 0; }

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