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Merge pull request #105 from ptersilie/nomoreentryblockcalls
Add pass disallowing calls in entry blocks.
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,10 @@ | ||
| #ifndef LLVM_TRANSFORMS_YK_NOCALLSINENTRYBLOCKS_H | ||
| #define LLVM_TRANSFORMS_YK_NOCALLSINENTRYBLOCKS_H | ||
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| #include "llvm/Pass.h" | ||
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| namespace llvm { | ||
| ModulePass *createYkNoCallsInEntryBlocksPass(); | ||
| } // namespace llvm | ||
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| #endif |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,107 @@ | ||
| // NoCallsInEntryBlocks.cpp - Ensure there are no calls in the first block. | ||
| // | ||
| // This pass splits up the entry block so that there are no calls inside it | ||
| // (one exception being the malloc call inserted by the shadowstack pass which | ||
| // will be applied later). This allows us to detect call backs from external | ||
| // functions more easily, which in turn simplifies our JITModBuilder | ||
| // implementation and fixes the soundness issue that existed in the old | ||
| // StackAdjust approach. | ||
| // | ||
| // As a simplified example, imagine this function: | ||
| // | ||
| // void foo(int argc) { | ||
| // if (argc == 0) { | ||
| // extfunc(foo) | ||
| // } | ||
| // } | ||
| // | ||
| // where `extfunc` may or may not call back to `foo`. Previously, this might | ||
| // result in a trace like | ||
| // | ||
| // foo.0 | ||
| // extfunc | ||
| // foo.0 | ||
| // ... | ||
| // | ||
| // Upon seeing the second `foo.0` we are unable to determine whether we are | ||
| // observing a callback to `foo` or are returning from `extfunc` which hasn't | ||
| // called foo. When running this pass we force `extfunc` not to be in the entry | ||
| // block, resulting in a trace like | ||
| // | ||
| // foo.0 | ||
| // foo.1 | ||
| // extfunc | ||
| // foo.1 | ||
| // ... | ||
| // | ||
| // Here it is clear that `extfunc` has not called `foo` as we are seeing block | ||
| // `foo.1` next. If `extfunc` had called `foo`, the next block would be | ||
| // `foo.0`. | ||
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| #include "llvm/Transforms/Yk/NoCallsInEntryBlocks.h" | ||
| #include "llvm/IR/BasicBlock.h" | ||
| #include "llvm/IR/Function.h" | ||
| #include "llvm/IR/IRBuilder.h" | ||
| #include "llvm/IR/Instructions.h" | ||
| #include "llvm/IR/Module.h" | ||
| #include "llvm/IR/Verifier.h" | ||
| #include "llvm/InitializePasses.h" | ||
| #include "llvm/Pass.h" | ||
| #include "llvm/Transforms/Yk/LivenessAnalysis.h" | ||
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| #define DEBUG_TYPE "yk-no-more-entryblock-calls" | ||
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| using namespace llvm; | ||
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| namespace llvm { | ||
| void initializeYkNoCallsInEntryBlocksPass(PassRegistry &); | ||
| } // namespace llvm | ||
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| namespace { | ||
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| class YkNoCallsInEntryBlocks : public ModulePass { | ||
| public: | ||
| static char ID; | ||
| YkNoCallsInEntryBlocks() : ModulePass(ID) { | ||
| initializeYkNoCallsInEntryBlocksPass(*PassRegistry::getPassRegistry()); | ||
| } | ||
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| bool runOnModule(Module &M) override { | ||
| LLVMContext &Context = M.getContext(); | ||
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| // split block at first function call | ||
| std::set<Instruction *> Calls; | ||
| for (Function &F : M) { | ||
| if (F.empty()) // skip declarations. | ||
| continue; | ||
| BasicBlock &BB = F.getEntryBlock(); | ||
| auto CurrFuncName = F.getName(); | ||
| for (Instruction &I : BB) { | ||
| if (isa<CallInst>(I)) { | ||
| Function *F = cast<CallInst>(I).getCalledFunction(); | ||
| BB.splitBasicBlock(&I); | ||
| break; | ||
| } | ||
| } | ||
| } | ||
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| #ifndef NDEBUG | ||
| // Our pass runs after LLVM normally does its verify pass. In debug builds | ||
| // we run it again to check that our pass is generating valid IR. | ||
| if (verifyModule(M, &errs())) { | ||
| Context.emitError("Stackmap insertion pass generated invalid IR!"); | ||
| return false; | ||
| } | ||
| #endif | ||
| return true; | ||
| } | ||
| }; | ||
| } // namespace | ||
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| char YkNoCallsInEntryBlocks::ID = 0; | ||
| INITIALIZE_PASS(YkNoCallsInEntryBlocks, DEBUG_TYPE, "no more entry block calls", | ||
| false, false) | ||
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| ModulePass *llvm::createYkNoCallsInEntryBlocksPass() { | ||
| return new YkNoCallsInEntryBlocks(); | ||
| } |