Question

Hi I made a simple hello world C program and I am compiling it like this :

gcc -c hello.c
ld hello.o -lc -o out

I get a warning from ld : ld : _start not found defaulting to ....

I do an objdump -D hello.o and I cannot find the _start routine in the output.
What am I missing here ?

Answer 1

You’re missing the crt* stuff which you will see if you link with gcc -v: crt1.o, crtend.o, crtn.o. Look at how gcc invokes collect2 (it’s visible with gcc -v) and use the same options for ld.

main function is not the executable entry point: some initialization for standard library is done before main (because it’s either impossible or illogical to do otherwise). Real entry point, which is _start by default, is in crt1.o which is always linked into your executable.