如何在LLVM IR中获取引用函数指针

Question

我正在编写一个LLVM模块传递，它将获得pthread_create中的第三个参数。根据手册页，pthread_create的功能原型是

int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine) (void *), void *arg);

例如，我的目标C源代码如下。

void *pthread_task(void *args) {
sleep(4);
return NULL;
}
int main(int argc, char *argv[]) {
pthread_t tid;
pthread_create(&tid, NULL, pthread_task, NULL);
pthread_join(tid, NULL);
return 0;
}

我想要输出"pthread_task"。我能够访问正确的函数并列出所有参数。然而，由于第三个参数是函数指针，我不知道如何访问它所指向的函数

我还附上了我如何实现我的模块通行证如下。

namespace {
~   int32_t indexOfPthreadCreate(CallGraphNode *node) {
~     for (int32_t i = 0; i < node -> size(); i++) {
~       Function *f = (*node)[i] -> getFunction();
~       if (f && f -> getName().compare("pthread_create") == 0) {
+         for (auto &A: f->args()) {
// I would like to access the third parameter of pthread_create here.
+           A.print(errs());
+         }
+         return i;
+       }
}
~     return -1;
}
struct PthreadScopeDetectPass : public ModulePass {
static char ID;
PthreadScopeDetectPass() : ModulePass(ID) { }
bool runOnModule(Module &M) override {
CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
uint32_t nSCC  = 0;
for (scc_iterator<CallGraph *> iterSCC = scc_begin(&CG); !iterSCC.isAtEnd(); ++iterSCC) {
auto nodes = *iterSCC;
for (CallGraphNode *node: nodes) {
Function *currFunc = node -> getFunction();
~           int32_t target_i = indexOfPthreadCreate(node);
~           if (target_i > 0 && currFunc) {
+             insertTimer(currFunc);
}
}
}
return true;
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesAll();
AU.addRequired<CallGraphWrapperPass>();
}
};
}

Answer 1

感谢@ant的评论。我已经解决了这个问题。以下是我解决问题的方法。

~   int32_t indexOfPthreadCreate(CallGraphNode *node) {
~     for (int32_t i = 0; i < node -> size(); i++) {
~       Function *f = (*node)[i] -> getFunction();
~       if (f && f -> getName().compare("pthread_create") == 0) {
+         for (auto &inst: instructions(f)) {
~           if (inst.getOpcode() == 56) {
~             CallInst *ci = dyn_cast<CallInst>(&inst);
~             if (ci && ci->getCalledFunction()->getName().compare("pthread_create") == 0) {
~               Function *pthread_task = dyn_cast<Function>(ci->getArgOperand(2));
~_              errs() << "pthread is going to execute " << pthread_task->getName() << "function n";
}
+           }
+           A.print(errs());
+         }
+         return i;
+       }
}
~     return -1;
}