I just read about the LLVM project and that it could be used to do static analysis on C/C++ codes using the analyzer Clang which the front end of LLVM. I wanted to know if it is possible to extract all the accesses to memory(variables, local as well as global) in the source code using LLVM.
Is there any inbuilt library present in LLVM which I could use to extract this information. If not please suggest me how to write functions to do the same.(existing source code, reference, tutorial, example...) Of what i have thought, is I would first convert the source code into LLVM bc and then instrument it to do the analysis, but don't know exactly how to do it.
I tried to figure out myself which IR should I use for my purpose ( Clang's Abstract Syntax Tree (AST) or LLVM's SSA Intermediate Representation (IR). ), but couldn't really figure out which one to use. Here is what I m trying to do. Given any C/C++ program (like the one given below), I am trying to insert calls to some function, before and after every instruction that reads/writes to/from memory. For example consider the below C++ program ( Account.cpp)
#include <stdio.h>
class Account {
int balance;
public:
Account(int b) {
balance = b;
}
int read() {
int r;
r = balance;
return r;
}
void deposit(int n) {
balance = balance + n;
}
void withdraw(int n) {
int r = read();
balance = r - n;
}
};
int main () {
Account* a = new Account(10);
a->deposit(1);
a->withdraw(2);
delete a;
}
So after the instrumentation my program should look like:
#include <stdio.h>
class Account {
int balance;
public:
Account(int b) {
balance = b;
}
int read() {
int r;
foo();
r = balance;
foo();
return r;
}
void deposit(int n) {
foo();
balance = balance + n;
foo();
}
void withdraw(int n) {
foo();
int r = read();
foo();
foo();
balance = r - n;
foo();
}
};
int main () {
Account* a = new Account(10);
a->deposit(1);
a->withdraw(2);
delete a;
}
where foo() may be any function like get the current system time or increment a counter .. so on. I understand that to insert function like above I will have to first get the IR and then run an instrumentation pass on the IR which will insert such calls into the IR, but I don't really know how to achieve it. Please suggest me with examples how to go about it.
Also I understand that once I compile the program into the IR, it would be really difficult to get 1:1 mapping between my original program and the instrumented IR. So, is it possible to reflect the changes made in the IR ( because of instrumentation ) into the original program.
In order to get started with LLVM pass and how to make one on my own, I looked at an example of a pass that adds run-time checks to LLVM IR loads and stores, the SAFECode's load/store instrumentation pass (http://llvm.org/viewvc/llvm-project/safecode/trunk/include/safecode/LoadStoreChecks.h?view=markup and http://llvm.org/viewvc/llvm-project/safecode/trunk/lib/InsertPoolChecks/LoadStoreChecks.cpp?view=markup). But I couldn't figure out how to run this pass. Please give me steps how to run this pass on some program say the above Account.cpp.
