死循环检测

LLVM介绍
FunctionPass
集成到Clang工具中
后记

本篇文章的目的是通过在循环体里插桩代码，用以检测循环是否发生了不可预期的死循环。

#include "stdio.h"
int main()
{int i = 0;for(; i < 21; i++){printf("%d \n", i);}return 0;
}

输出

0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
many loop count 21

自动判断是否超出了预期的循环次数。

LLVM介绍

LLVM是新一代的编译工具，强大的模块化支持，让程序员很方便的介入到编译过程中的各个方面，本篇文章主要利用函数处理阶段来插桩部分代码。

FunctionPass

FunctionPass是LLVM在处理函数代码生成时，会调用的Pass模块。本篇文章中直接在LLVM自带的HelloWorldPass里加入我们的代码。

PreservedAnalyses HelloWorldPass::run(Function &F,FunctionAnalysisManager &AM) {LoopInfo *LI = &AM.getResult<LoopAnalysis>(F);errs() << F.getName() << " loopcount:" <<  LI->getTopLevelLoopsVector().size() << "\n";Type *intType = Type::getInt32Ty(F.getContext());std::vector<Type *> printfArgsTypes({Type::getInt8PtrTy(F.getContext())});FunctionType *printfType = FunctionType::get(intType, printfArgsTypes, true);auto printfFunc = F.getEntryBlock().getModule()->getOrInsertFunction("printf", printfType);for(auto &l : LI->getTopLevelLoopsVector()){auto pp = l->getLoopPredecessor();if(pp){IRBuilder<> builderInit(pp->getFirstNonPHI());      auto pLoopCount = builderInit.CreateAlloca(builderInit.getInt32Ty(), nullptr, "loopcount");builderInit.CreateStore(ConstantInt::get(builderInit.getInt32Ty(), 0), pLoopCount);auto pB = l->getHeader();builderInit.SetInsertPoint(pB->getFirstNonPHI());auto *addL = builderInit.CreateLoad(builderInit.getInt32Ty(), pLoopCount, "loadLoopCount");auto *one = ConstantInt::get(builderInit.getInt32Ty(), 1);auto *pRest = builderInit.CreateAdd(addL, one, "inc loopCount");builderInit.CreateStore(pRest, pLoopCount);auto pBExit = l->getExitBlock();if(pBExit != nullptr){builderInit.SetInsertPoint(pBExit->getFirstNonPHI());auto *addL = builderInit.CreateLoad(builderInit.getInt32Ty(), pLoopCount, "loadLoopCount");auto *n100W = ConstantInt::get(builderInit.getInt32Ty(), 20);auto *pCmp = cast<ICmpInst>(builderInit.CreateCmp(CmpInst::Predicate::ICMP_UGE, addL, n100W, "Cmp"));// builderInit.CreateCmp();//auto pAssert = BasicBlock::Create(pBExit->getContext(), "assert");Instruction *Brnch =SplitBlockAndInsertIfThen(pCmp, pCmp->getNextNode(), false);builderInit.SetInsertPoint(Brnch);Value *puts_params[] = {builderInit.CreateGlobalStringPtr("many loop count %d \n", "loopttip"),addL};builderInit.CreateCall(printfFunc, puts_params, "printlog");// auto pIfThen = SplitBlockAndInsertIfThen(pCmp, pBExit->getFirstNonPHI(), false, nullptr, (DominatorTree*)nullptr, nullptr, pAssert);// builderInit.Insert(pIfThen, "ifthen");//pBExit->getModule()->getOrInsertFunction()//builderInit.CreateSelect(pCmp, )}     }}return PreservedAnalyses::none();
}

生成的IR对比

; ModuleID = 'test.c'
source_filename = "test.c"
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"@.str = private unnamed_addr constant [5 x i8] c"%d \0A\00", align 1
@loopttip = private unnamed_addr constant [21 x i8] c"many loop count %d \0A\00", align 1; Function Attrs: nofree nounwind uwtable
define dso_local i32 @main() local_unnamed_addr #0 {%1 = alloca i32, align 4store i32 0, i32* %1, align 4%2 = load i32, i32* %1, align 4br label %33:                                                ; preds = %0, %3%4 = phi i32 [ %2, %0 ], [ %6, %3 ]%5 = phi i32 [ 0, %0 ], [ %8, %3 ]%6 = add i32 %4, 1%7 = call i32 (i8*, ...) @printf(i8* noundef nonnull dereferenceable(1) getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i32 noundef %5)%8 = add nuw nsw i32 %5, 1%9 = icmp eq i32 %8, 21br i1 %9, label %10, label %3, !llvm.loop !310:                                               ; preds = %3store i32 %6, i32* %1, align 4%11 = load i32, i32* %1, align 4%12 = icmp ugt i32 %11, 19br i1 %12, label %13, label %1513:                                               ; preds = %10%14 = call i32 (i8*, ...) @printf(i8* nonnull dereferenceable(1) getelementptr inbounds ([21 x i8], [21 x i8]* @loopttip, i64 0, i64 0), i32 %11)br label %1515:                                               ; preds = %10, %13ret i32 0
}; Function Attrs: nofree nounwind
declare dso_local noundef i32 @printf(i8* nocapture noundef readonly, ...) local_unnamed_addr #1attributes #0 = { nofree nounwind uwtable "frame-pointer"="none" "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
attributes #1 = { nofree nounwind "frame-pointer"="none" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }!llvm.module.flags = !{!0, !1}
!llvm.ident = !{!2}!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{i32 7, !"uwtable", i32 2}
!2 = !{!"clang version 15.0.0 (https://github.com/llvm/llvm-project.git a4d2943bf6b350ea62745ab25c7dcc2f1d17a470)"}
!3 = distinct !{!3, !4, !5}
!4 = !{!"llvm.loop.mustprogress"}
!5 = !{!"llvm.loop.unroll.disable"}

; ModuleID = '../llvm-test/test.ll.out'
source_filename = "test.c"
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"@.str = private unnamed_addr constant [5 x i8] c"%d \0A\00", align 1
@loopttip = private unnamed_addr constant [21 x i8] c"many loop count %d \0A\00", align 1
@loopttip.1 = private unnamed_addr constant [21 x i8] c"many loop count %d \0A\00", align 1; Function Attrs: nofree nounwind uwtable
define dso_local i32 @main() local_unnamed_addr #0 {%loopcount = alloca i32, align 4store i32 0, i32* %loopcount, align 4%1 = alloca i32, align 4store i32 0, i32* %1, align 4%2 = load i32, i32* %1, align 4br label %33:                                                ; preds = %3, %0%4 = phi i32 [ %2, %0 ], [ %6, %3 ]%5 = phi i32 [ 0, %0 ], [ %8, %3 ]%loadLoopCount = load i32, i32* %loopcount, align 4;这里自增循环次数%"inc loopCount" = add i32 %loadLoopCount, 1store i32 %"inc loopCount", i32* %loopcount, align 4%6 = add i32 %4, 1%7 = call i32 (i8*, ...) @printf(i8* noundef nonnull dereferenceable(1) getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i32 noundef %5)%8 = add nuw nsw i32 %5, 1%9 = icmp eq i32 %8, 21br i1 %9, label %10, label %3, !llvm.loop !310:                                               ; preds = %3%loadLoopCount1 = load i32, i32* %loopcount, align 4%Cmp = icmp uge i32 %loadLoopCount1, 20              ;这里判断循环次数br i1 %Cmp, label %11, label %1211:                                               ; preds = %10%printlog = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([21 x i8], [21 x i8]* @loopttip.1, i32 0, i32 0), i32 %loadLoopCount1)br label %1212:                                               ; preds = %10, %11store i32 %6, i32* %1, align 4%13 = load i32, i32* %1, align 4%14 = icmp ugt i32 %13, 19br i1 %14, label %15, label %1715:                                               ; preds = %12%16 = call i32 (i8*, ...) @printf(i8* nonnull dereferenceable(1) getelementptr inbounds ([21 x i8], [21 x i8]* @loopttip, i64 0, i64 0), i32 %13)br label %1717:                                               ; preds = %15, %12ret i32 0
}; Function Attrs: nofree nounwind
declare dso_local noundef i32 @printf(i8* nocapture noundef readonly, ...) local_unnamed_addr #1attributes #0 = { nofree nounwind uwtable "frame-pointer"="none" "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
attributes #1 = { nofree nounwind "frame-pointer"="none" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }!llvm.module.flags = !{!0, !1}
!llvm.ident = !{!2}!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{i32 7, !"uwtable", i32 2}
!2 = !{!"clang version 15.0.0 (https://github.com/llvm/llvm-project.git a4d2943bf6b350ea62745ab25c7dcc2f1d17a470)"}
!3 = distinct !{!3, !4, !5}
!4 = !{!"llvm.loop.mustprogress"}
!5 = !{!"llvm.loop.unroll.disable"}

集成到Clang工具中

//clang/lib/CodeGen/BackendUtil.cpp
void EmitAssemblyHelper::RunOptimizationPipeline(BackendAction Action, std::unique_ptr<raw_pwrite_stream> &OS,std::unique_ptr<llvm::ToolOutputFile> &ThinLinkOS) {....PB.registerScalarOptimizerLateEPCallback([](FunctionPassManager &FPM, OptimizationLevel Level) {FPM.addPass(HelloWorldPass());});....}

后记

本篇文章只是初试LLVM做的一个练习课题，仅供参考。

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【LLVM实践】死循环插桩检测

死循环检测

LLVM介绍

FunctionPass

集成到Clang工具中

后记

【LLVM实践】死循环插桩检测相关推荐

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