How to use AddressSanitizer to debug C++ memory access errors?

AddressSanitizer (ASan) detects memory errors by checking every memory access in a C++ program. To enable ASan, add the -fsanitize=address flag to the compile command. When enabled, ASan will report errors such as reading an uninitialized variable, writing out of bounds, or using freed memory. ASan can also be used to detect memory leaks, developers can enable this feature using the -fsanitize=leak flag.

How to use AddressSanitizer to debug C++ memory access errors

Introduction
AddressSanitizer (ASan) is A tool that helps detect memory-related errors in C++ programs, such as reading an uninitialized variable, writing out of bounds, or using freed memory. ASan works by inspecting every memory access of a program and reporting any violations of security rules.

Enable ASan
To enable ASan, just add the -fsanitize=address flag to the compile command. This flag links the ASan library into the program and enables additional checks on memory accesses.

g++ -fsanitize=address main.cpp -o main

Run the program
After enabling ASan, you can run the program as usual. However, ASan now detects and reports any memory access errors. If an error occurs in the program, ASan will print an error message and terminate the program. The error message will contain detailed information about the error, such as the line of code where the error occurred and which memory address was illegally accessed.

Example
Let us consider a simple C++ program that uses uninitialized variables:

int main() {
  int x;
  std::cout << x << std::endl;  // 未初始化的变量
}

Compiling and running this program using ASan produces the following output :

==14569==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7fffffffd7e0 at pc 0x40102e bp 0x7fffffffd770 sp 0x7fffffffd7d0
  READ of size 4 at 0x7fffffffd7e0 thread T0
    #0 0x40102c in main /home/user/asan_example.cpp:5
    #1 0x7f40a7bddc9c in __libc_start_main /build/glibc-eXfix9/glibc-2.35/csu/../csu/libc-start.c:314

This error message tells us:

• A stack usage out of range error occurred.
• The error occurs on line 5 of the main function.

By carefully inspecting the code, we can see that the error is caused by trying to use an uninitialized variable x.

Practical Case: Memory Leak
ASan can also be used to detect memory leaks, which refers to problems caused by a program allocating memory but not releasing it. A memory leak causes a program's memory usage to increase over time, eventually leading to crashes or performance degradation.

To detect memory leaks, you need to use the -fsanitize=leak compilation flag. This flag enables additional checks on memory usage and reports any memory blocks that are still allocated when the program terminates.

Conclusion
AddressSanitizer is a powerful tool that helps detect memory-related errors in C++ programs. By enabling ASan and using clear error messages, developers can quickly and accurately identify and fix these errors, improving the reliability and security of their programs.

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