Can you run a user-defined pass before ASAN sanitizer?

Question

I compile my code with -fsanitize=address switch. I have my own llvm pass that I want to execute. By the time the pass starts, I can see that the ASAN pass was made. Is it possible to run my pass before the ASAN pass?

Answer 1

I‘ve also tried to run my pass before the ASAN pass in different ways to instrument my program at BasicBlock-level.

And this seems to be available for me:

Register a "StandardPasses" with EP_EarlyAsPossible flag which makes your pass works earlier than ASAN.

static RegisterStandardPasses Y(PassManagerBuilder::EP_EarlyAsPossible,
                                [](const PassManagerBuilder &Builder,
                                   legacy::PassManagerBase &PM) {
                                  PM.add(new MyPass());
                                });

Compile your pass as a ".so" file.

Then use clang -Xclang -load -Xclang xxYourPassxx.so -fsanitize=address main.c -o main to compile your code.

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I also compiled the main.bc & main.ll for checking. And the results show me that my instrumentation doesn't appear in ASAN's block (Because my pass runs before ASAN).