Index: compiler-rt/test/asan/TestCases/Helpers/underflow.cc =================================================================== --- /dev/null +++ compiler-rt/test/asan/TestCases/Helpers/underflow.cc @@ -0,0 +1 @@ +int YYY[3]={1,2,3}; Index: compiler-rt/test/asan/TestCases/global-underflow.cc =================================================================== --- /dev/null +++ compiler-rt/test/asan/TestCases/global-underflow.cc @@ -0,0 +1,17 @@ +// RUN: %clangxx_asan -O0 -mllvm -asan-meta-separate-section %s %p/Helpers/underflow.cc -o %t && not %run %t 2>&1 | FileCheck %s +// RUN: %clangxx_asan -O1 -mllvm -asan-meta-separate-section %s %p/Helpers/underflow.cc -o %t && not %run %t 2>&1 | FileCheck %s +// RUN: %clangxx_asan -O2 -mllvm -asan-meta-separate-section %s %p/Helpers/underflow.cc -o %t && not %run %t 2>&1 | FileCheck %s +// RUN: %clangxx_asan -O3 -mllvm -asan-meta-separate-section %s %p/Helpers/underflow.cc -o %t && not %run %t 2>&1 | FileCheck %s + +int XXX[2] = {2, 3}; +extern int YYY[]; +#include +int main(int argc, char **argv) { + memset(XXX, 0, 2*sizeof(int)); + // CHECK: {{READ of size 4 at 0x.* thread T0}} + // CHECK: {{ #0 0x.* in main .*global-underflow.cc:}}[[@LINE+3]] + // CHECK: {{0x.* is located 4 bytes to the left of global variable}} + // CHECK: {{.*YYY.* of size 12}} + int res = YYY[-1]; + return res; +} Index: llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp =================================================================== --- llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp +++ llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp @@ -176,6 +176,11 @@ "asan-force-dynamic-shadow", cl::desc("Load shadow address into a local variable for each function"), cl::Hidden, cl::init(false)); +static cl::opt ClMetaInSeparateSection( + "asan-meta-separate-section", + cl::desc("Place ASan global metadata into a separate section"), + cl::Hidden, cl::init(false)); + // This flag limits the number of instructions to be instrumented // in any given BB. Normally, this should be set to unlimited (INT_MAX), @@ -1876,6 +1881,13 @@ M, ArrayOfGlobalStructTy, false, GlobalVariable::InternalLinkage, ConstantArray::get(ArrayOfGlobalStructTy, MetadataInitializers), ""); + // Place ASan metadata into a separate section similarly to how it's done + // for -fdata-sections (see InstrumentGlobalsELF() or InstrumentGlobalsMachO()) + // to avoid stepping into it on global underflow in first symbols of data + // sections. + if (ClMetaInSeparateSection) + AllGlobals->setSection(getGlobalMetadataSection()); + IRB.CreateCall(AsanRegisterGlobals, {IRB.CreatePointerCast(AllGlobals, IntptrTy), ConstantInt::get(IntptrTy, N)});