如何使用 GDB 在可执行文件的 c++ 代码的第一行停止？

Question

I have a C++ project. After using CMake compile in debug mode, it generates many executables.

I want to debug an executable suppose it called A.

But I don't sure where is the A's main function, so I want to use gdb to debug A and want to stop at its main function's first line. How should I do? Thank you very much!

Answer 1

To simply run until we reach main, we simply can

> start

which will set a temporary breakpoint at main and starts execution.

If you always want to break at main, even if you restart your program, you can add a persistent breakpoint and run.

>b main
>run

As we have maybe a lot of code running before main, especially if constructors of global objects are needed, it makes sense to beak already on the first instruction the program have. In that case we can use

> starti

which will stop on the first executed assembler instruction

We also can go to dedicated sections of the startup procedure, if we know the symbol names here. One example is _init on which you also can stop if needed. To get a more detailed list of possible breakpoints see: gcc initialization

If you need to stop on a known constructor, you can also set a breakpoint on all constructors of a class type if you simply use the constructors name, here given for a class A as example. This is very helpful if a global object is created before main is started. It helps a lot in the case you have dependent global objects which may fail as we all know static initialization order fiasco

>b A::A