Date: Fri, 13 Nov 1998 23:09:55 +0200 (SAT) From: Robert Nordier <rnordier@nordier.com> To: crossd@cs.rpi.edu (David E. Cross) Cc: rnordier@nordier.com, ru@ucb.crimea.ua, hackers@FreeBSD.ORG Subject: Re: FreeBSD on i386 memory model Message-ID: <199811132109.XAA13342@ceia.nordier.com> In-Reply-To: <Pine.SGI.4.05.9811131447590.6396-100000@o2.cs.rpi.edu> from "David E. Cross" at "Nov 13, 98 02:49:42 pm"
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David E. Cross wrote:
>
> That is great. Could you sprinkle a comment or 2 as to what it is doing?
>
> ie, I am not sure what the 'call .+0x5' and 'lcall $0x7,0x0' do.
The "call .+0x5" just calls the location corresponding to the start
of the next instruction (the '.' is the current location and a call
is encoded as 5 bytes). The "lcall 0x7,0x0" does a system call.
# Get offset of main in %ebp
main: call .+0x5
popl %ebp
subl $0x5,%ebp
# write(STDOUT_FILENO, msg, sizeof(msg));
pushl $msg.1-msg
leal msg-main(%ebp),%eax
pushl %eax
pushl $0x1
movl $0x4,%eax # SYS_write
call .+0x5
lcall $0x7,$0x0
# exit(0);
pushl $0x0
movl $0x1,%eax # SYS_exit
call .+0x5
lcall $0x7,$0x0
msg: .ascii "hello, world!\n"
msg.1:
It is really just intended as a curiosity, and is neither very
idiomatic nor very correct. :-)
--
Robert Nordier
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