return() vs. exit() vs. _exit()

[Joseph S. D. Yao]

In article <178 at rexago1.UUCP> rich at rexago1.UUCP (K. Richard Magill) writes:
>What's the difference between leaving main by return() vs exit() vs _exit()?

Functionally, return and exit should be identical.  Your 'lint'
(s5r2.0v2) prob'ly complains if you use exit() tho.  The code goes
roughly like:
[C header, crt0.s:]
	push	envp
	push	argv
	push	argc
	call	$3, _main
	push	r0
	call	$1, $_exit
	sys	$exit_system_call
	halt
Note that exit(main(argc, argv, envp)) is the effect.

The exit() code resembles:
exit(val)
  int val;
{
	register FILE *fp;

	for (fp = _iob; fp < &_iob[NIOBUFS]; fp++)
		if fp has been opened
			fclose(fp);
	_exit(val);
}
..........
__exit:
	move	arg to r0
	sys	$exit_system_call

Shared and local memory are reclaimed by the kernel after an exit()
system call.

>                               ...  What is a gate 4, 8?

Got my curiosity piqued.
-- 

	Joe Yao		hadron!jsdy at seismo.{CSS.GOV,ARPA,UUCP}