This is cool. I've been working on something similar[0]. It only takes a few more lines to add some of the other useful libc/posix/sysv things. My eventual goal is to rewrite asmutils'[1] httpd [2] in C and get a binary about 2-3x in size (2-3K).

[0] https://github.com/lpsantil/rt0

[1] http://asm.sourceforge.net/asmutils.html

[2] https://github.com/leto/asmutils/blob/master/src/httpd.asm