From mboxrd@z Thu Jan  1 00:00:00 1970
To: 9fans@cse.psu.edu
Subject: Re: [9fans] booting an AlphaPC 164
From: David Gordon Hogan <dhog@plan9.bell-labs.com>
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Date: Mon, 25 Jun 2001 15:22:53 -0400
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> If i understand the boot process correctly, it has just jumped into
> _main() in/sys/src/9/alphapc/l.s from gokernel() in /sys/src/9/boot/alphapc/exec.c
> By adding RET to various points of _main() in l.s, i am thinking it is hanging
> at the spot marked:

> TEXT	_main(SB), $-8
> 	MOVQ	$setSB(SB), R29
> 	MOVQ	R29, R16
> 	CALL_PAL $PALwrkgp
> 	MOVQ	$mach0(SB), R(MACH)
> 	MOVQ	$(BY2PG-8)(R(MACH)), R30   <-------------
> 	MOVQ	R31, R(USER)
> 	MOVQ	R31, 0(R(MACH))
> 
> If i understand correctly this just sets the stack pointer to last quadword 
> of the page containing the mach structure.

Although the RET instruction doesn't use SP itself, the caller isn't going to
be too happy after you change it.  Use the "CALL_PAL $PALhalt" instruction
to find out where it's really hanging.  If it makes it to C, you can insert calls
to firmware().

> We get the same behavior w/ both the terminal and cpu kernels, and
> also the same if we try it on an ev6 machine.  I found a post about
> using the -x flag to 7l, but that does not seem to help.

That's only neccessary for older CPUs.  You'll be taking a significant
performance hit by using it otherwise, and some of the device drivers
may not work.