LoadInst和StoreInst值和地址LLVM [英] LoadInst and StoreInst Values and addresses LLVM

问题描述

我有一个文件print.c，它具有两个功能:

I have a file print.c, which has two functions:

void printLoad(...) {
  // print address and value of memory location from which value
  printf("address=... value=...", ...); 
}

void printStore(...) {
  // print address and value of memory location from which value 
}

我有一个 LLVM 传递，它遍历指令并在当前指令(加载/存储指令)之后添加 CallInst 指令 printLoad 或 printStore(取决于指令类型).

I have an LLVM pass which iterates over the instructions and adds CallInst instruction either printLoad or printStore (depending on the instruction type) after the current one (load/store inst).

为了调用此printStore或printLoad，我需要向CallInst :: Create函数添加适当的参数，这些参数是内存位置的地址和值.

In order to call this printStore or printLoad I need to add appropriate arguments to CallInst::Create function, which are the address and the value of the memory location.

这是我要实现的示例:

define void @mains() #0 {
  %1 = alloca i32, align 4
  %2 = alloca i32, align 4
  store i32 0, i32* %1, align 4
  store i32 5, i32* %1, align 4
  store i32 2, i32* %2, align 4
  store i32 4, i32* %2, align 4
  %3 = load i32, i32* %2, align 4
  %4 = add nsw i32 %3, 5
  store i32 %4, i32* %1, align 4
  ret void
}

The output should be:
  store instruction: 
    address=...   // address of %1
    value=0
  ...
  ...
  ...
  load instruction:
    address=...  // address of %2
    value=4
  store instruction:
    address=...  // address of %1
    value=9

到目前为止的进展:

我可以使用LoadInst/StoreInst上的getPointerOperand()获取操作数的地址.

I am able to get the addresses of the operands using getPointerOperand() on LoadInst/StoreInst.

我也可以通过将操作数强制转换为ConstantInt来获取前4条存储指令中StoreInst的值，但是我不知道如何提取最后一条StoreInst中的值.甚至有可能吗?

I can also get the value of StoreInst in the first 4 store instructions by casting the operand to ConstantInt, but I don't know how to extract the value in the last StoreInst. Is it even possible?

已编辑

使用

void printLoad(int32_t p) 

和

Constant *hookLoadFunc = M.getOrInsertFunction("printLoad", Type::getVoidTy(M.getContext()), Type::getInt32Ty(M.getContext()));

.

  %1 = alloca i32, align 4
  %2 = alloca i32, align 4
  %3 = alloca i32, align 4
  store i32 0, i32* %1, align 4
  call void @printStore(i32 0)
  store i32 0, i32* %2, align 4
  call void @printStore(i32 0)
  store i32 5, i32* %2, align 4
  call void @printStore(i32 5)
  store i32 2, i32* %3, align 4
  call void @printStore(i32 2)
  store i32 4, i32* %3, align 4
  call void @printStore(i32 4)
  %4 = load i32, i32* %3, align 4
  %5 = add nsw i32 %4, 5
  store i32 %5, i32* %2, align 4
  call void @printStore(i32 %5)
  ret i32 0
  %2 = alloca i32, align 4
  store i32 %0, i32* %2, align 4
  call void @printStore(i32 %0)
  %3 = load i32, i32* %2, align 4
  %4 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([22 x i8], [22 x i8]* @.str, i32 0, i32 0), i32 %3)
  ret void
  %2 = alloca i32, align 4
  store i32 %0, i32* %2, align 4
  call void @printStore(i32 %0)
  %3 = load i32, i32* %2, align 4
  %4 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([22 x i8], [22 x i8]* @.str.1, i32 0, i32 0), i32 %3)
  ret void

这会导致分段错误:运行时为11.

This causes Segmentation fault: 11 when run.

已解决:

弄清楚我有无限循环(由于递归). printStore 实际上使用加载/存储指令，从而创建另一个对 printStore 的调用，依此类推.

Figured out that I had infinity loop (due to recursion). printStore actually uses load/store instructions, thus creating another call to printStore and so on.

推荐答案

假设您有一个表示 printLoad()和 printStore的 llvm :: Function ():

Assuming that you have an llvm::Function that represents printLoad() and printStore():

llvm::Function * print_load = ....
llvm::Function * print_store = ...

您可以为每个 LoadInst 和 StoreInst 发出 CallInst .

对于LoadInst:

LoadInst * some_load = ...
Value * address_of_load = some_load->getOperand(0);
Value * print_load_arguments[] = { address_of_load, some_load };

// Insert a CallInst just after the load.
CallInst::Create(print_load, print_load_arguments )->insertAfter( some_load );

请记住，在llvm中， LoadInst 加载的值与 LoadInst 本身相同.

Remember that in llvm the value loaded by the LoadInst is the same thing as the LoadInst itself.

对于 StoreInst:

StoreInst * some_store = ...
Value * value_to_store = some_store->getOperand(0);
Value * address_of_store = some_store->getOperand(1);
Value * print_store_arguments[] = { address_of_store, value_to_store };

// Insert a CallInst just after the store.
CallInst::Create(print_store, print_store_arguments)->insertAfter(some_store);

如果所有类型都匹配，这将起作用.否则，您必须在调用 printStore()或 printLoad()之前插入 BitCast 指令.

This will work if all the types match. Otherwise, you have to insert BitCast instructions just before calling printStore() or printLoad().

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