To observe exactly what is one on each step, use:
gcc -v main.c
The exact steps are determined by the spec file, https://gcc.gnu.org/onlinedocs/gcc-4.8.1/gcc/Spec-Files.html You can view the default with:
gcc -dumpspecs
You can add your own specs after the default with:
gcc -specs=file
Generate all external intermediate steps (.i, .s, .o) in the current directory:
gcc -save-temps a.c
gcc is a high level wrapper to multiple compilation steps which are done by different programs.
Only expanded macros with the C preprocessor:
cpp a.c > a.i
cpp b.c > b.i
Different languages have different preprocessors
Generate human readable assembly code:
gcc -S a.i -o a.s
gcc -S b.i -o b.s
Specify format:
gcc -masm=att -S a.c -o a.s
gcc -masm=intel -S a.c -o a.s
Default format: AT&T which is historically what has larger GCC support.
Make machine code from assembly code:
as -o a.o a.s
as -o b.o b.s
This transforms human readable formats into binary object files
Make machine code from C directly:
gcc -c a.c -o a.o
gcc -c b.c -o b.o
Link object files into single executable:
ld -o ab.out a.o b.o
Expects main to be defined (actual ELF entry point is _start) TODO this does not link to the stdlib. How to make it?
All above steps in one:
gcc a.c b.c -o ab.out
If you use make, it is faster to generate .o and keep them, since if the source does not change, make will not recompile the corresponding .o