Practical Reverse Engineering p. 35 #3

Question number 3 on page 35 of Practical Reverse Engineering is as follows:

In some of the assembly listings, the function name has a @ prefix followed by a number. Explain when and why this decoration exists.

This is a compiler ABI decoration used with stdcall. The function name is also prefixed with an underscore. The number after the @ sign tells us the amount of bytes in the parameters.

BOOL WINAPI DllMain(
  _In_  HINSTANCE hinstDLL,
  _In_  DWORD fdwReason,
  _In_  LPVOID lpvReserved
);

The C function becomes the following symbol after compilation:

_DllMain@12