From: "Gary D. Thomas" <gary.thomas@mind.be>
To: jwalden@digitalatlantic.com
Cc: Linux PPC embedded <linuxppc-embedded@lists.linuxppc.org>
Subject: Re: Stack Frame Calc Problem in head_4xx.S
Date: 03 May 2003 16:21:39 -0600 [thread overview]
Message-ID: <1052000497.2537.5413.camel@hermes> (raw)
In-Reply-To: <EGEGIJHKDKJGAJMGIDPNGEOPCLAA.jwalden@digitalatlantic.com>
On Sat, 2003-05-03 at 15:20, Jerry Walden wrote:
> Greetings:
>
> I am having trouble understanding what is happening to my stack pointer.
>
> At line 1 r1 = 0x03f9_ebe8
>
> After line 15 executes r1 = 0xc00f4ff0
> which seems fine so far (according to the map file it is pointing to the
> proper location)
>
> After line 16 executes r1=0xc00f6ff0
> which is still within the bounds of init_task_union
>
> After line 17 execute r1 = 0xc00f6fe0 which seems like a problem to me,
> because it is not with the
> bounds of init_task_union - (see map file below)
>
Why do you think this? It seems that init_task_union comprises the
space from 0xc00f4ff0..0xc00f6ff0. That value is certainly within
that range.
> I would expect r1 to be within the bounds of init_task_union after this code
> is executed -
> is my guess correct? If so how is it possible that line 17 comes up with
> the result
> that it did?
Read how 'stwu' works. After the store takes place, r1 is updated
with the new value. In other words
stwu r0,-STACK_FRAME_OVERHEAD(r1)
means
[r1] = r0
r1 = r1 - STACK_FRAME_OVERHEAD(r1)
which is exactly the results you are getting.
>
> TASK_UNION_SIZE = 8192
> STACK_FRAME_OVERHEAD = 16
>
> Thanks for any help
>
> Jerry
>
> 1 start_here:
> 2
> 3 /* ptr to current */
> 4 lis r2,init_task_union@h
> 5 ori r2,r2,init_task_union@l
> 6
> 7 /* ptr to phys current thread */
> 8 tophys(r4,r2)
> 9 addi r4,r4,THREAD /* init task's THREAD */
> 10 mtspr SPRG3,r4
> 11 li r3,0
> 12 mtspr SPRG2,r3 /* 0 => r1 has kernel sp */
> 13
> 14 /* stack */
> 15 addi r1,r2,TASK_UNION_SIZE
> 16 li r0,0
> 17 stwu r0,-STACK_FRAME_OVERHEAD(r1)
>
>
> c00f4ff0 D init_task_union
> c00f6ff0 d aligninfo
> c00f70f0 D cpuinfo_op
> c00f7100 D cpu_specs
> c00f7280 D ppc_htab_operations
>
>
>
> Jerry Walden
> Program Manager
> Digital Atlantic Inc
> http://www.digitalatlantic.com
> jwalden@digitalatlantic.com
> 1-877-494-6073 x407
> cell - 703-431-2413
>
>
--
Gary D. Thomas <gary.thomas@mind.be>
** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
next prev parent reply other threads:[~2003-05-03 22:21 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-05-03 21:20 Stack Frame Calc Problem in head_4xx.S Jerry Walden
2003-05-03 22:21 ` Gary D. Thomas [this message]
2003-05-03 23:08 ` Jerry Walden
2003-05-05 1:41 ` Erik Christiansen
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