This example is with clang 15 using -O3.
Check it out on Godbolt: https://godbolt.org/z/Pd31fGKTe
#include <iostream>
int hello = printf("Hello World!\n");
int main() {
printf("main()");
}
Output is as expected from the rules of C++ initialization.
Hello World!
main()
What is not expected to me is the assembly code:
main: # @main
push rax
lea rdi, [rip + .L.str.2]
xor eax, eax
call printf@PLT
xor eax, eax
pop rcx
ret
_GLOBAL__sub_I_example.cpp: # @_GLOBAL__sub_I_example.cpp
push rbx
lea rbx, [rip + std::__ioinit]
mov rdi, rbx
call std::ios_base::Init::Init()@PLT
mov rdi, qword ptr [rip + std::ios_base::Init::~Init()@GOTPCREL]
lea rdx, [rip + __dso_handle]
mov rsi, rbx
call __cxa_atexit@PLT
lea rdi, [rip + .L.str]
xor eax, eax
call printf@PLT
mov dword ptr [rip + hello], eax
pop rbx
ret
hello:
.long 0 # 0x0
.L.str:
.asciz "Hello World!\n"
.L.str.2:
.asciz "main()"
It seems to me that main: is not the entry point, but _GLOBAL__sub_I_example.cpp: instead. I believe this because if not I think the program would ouput main() first, but it doesn't. What confuses me is that I don't get how the code from the main: label gets called. If _GLOBAL__sub_I_example.cpp: is the entry point, then why does it return something and how does the program ever run the code with the main label.
