Path: utzoo!mnetor!uunet!husc6!uwvax!oddjob!ncar!ames!oliveb!sun!gorodish!guy
From: guy@gorodish.Sun.COM (Guy Harris)
Newsgroups: comp.unix.wizards
Subject: Re: sun-3 dbx, arguments, hacking, help...
Message-ID: <50709@sun.uucp>
Date: 25 Apr 88 16:05:20 GMT
References: <1641@homxb.UUCP>
Sender: news@sun.uucp
Lines: 23
Keywords: Kludge, Hack, Hack

> 	HELP!!!  I need to know how `dbx' knows how many arguments are on the
> stack when you do the `where' command on a SUN 3.

By looking at the code following the call to see how many bytes it pops off the
stack.  (I checked the "dbx" source.)

> 	Now,  dbx KNOWS how many 4 byte arguments are there.  You do not have
> to compile with -g,   and it does not look in a symbol table and see how many
> are supposed to be there,   it knows even for function with a variable number
> of arguments.  Try the following program:

I did, and discovered that it does *not* get the argument count right on the
last call, because, as you indicate, the optimizer gets rid of the
stack-cleaning code.  It thinks "go" was called with zero arguments in the last
call.

> P.S.
> 	This will probably be impossible on a SUN-4

Make that "certainly will be impossible on a Sun-4", or on any other machine
that 1) passes arguments in registers and 2) has a compiler that does
sufficient optimization.  Perhaps not impossible, but at least *extremely*
difficult.