Writing device drivers in C, and then using the -S flag ... have you seen the output gcc -S on Linux (Ubuntu) returns for a trivial hello world program? ;)
Low level assembly is what you want, that presumably includes interfacing with you favorite C code.
Calling conventions, stack frames and so on.
Besides, the boilerplate runtime stuff has nothing to do with writing kernel code, so a 'trivial hello world' program will have a lot of cruft added to it:
.file "hello.c"
.section .rodata
.LC0:
.string "helo, world!"
.text
.globl main
.type main, @function
main:
leal 4(%esp), %ecx
andl $-16, %esp
pushl -4(%ecx)
pushl %ebp
movl %esp, %ebp
pushl %ecx
subl $20, %esp
movl $.LC0, (%esp)
call puts
addl $20, %esp
popl %ecx
popl %ebp
leal -4(%ecx), %esp
ret
.size main, .-main
.ident "GCC: (Ubuntu 4.3.3-5ubuntu4) 4.3.3"
.section .note.GNU-stack,"",@progbits
Note the stack frame alignment trick, the fact that 'printf' was specified in the source but puts is being called!
I think I must have coded myself to the moon and back by now if you'd print it all out on fanfold paper (in C, mostly), but the joy of getting a little OS to boot up from nothing is never going to pale in comparison to installing framework X and building some web-app. No matter how successful.
Web-apps make substantially more $ though...