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Message
From: Matjaz Breskvar<phoenix@o...>
Date: Wed May 4 01:30:07 CEST 2005
Subject: [openrisc] Starting Stack Value and arguments passing
* Balaji V. Iyer (bviyer@n...) wrote:
> Hello Everyone,
> I have a couple questions about stack and register values
> initialization. I am also "cut and pasting" a copy of the _start from
> the object dump of a simple file. My question is, what is the stack
> register (r1) initialized as? Also, when we have a main function like
> this:
well this would depend on the OS. if you were running on uclinux userspace
stack would be somewhere in the uniform memory. On linux though userspace
stack is at the top of the user addressable space, just below 0x80000000 in
or32 case.
> int main(int argc, char *argv[]), How are the argc and argv passed into
> the function. In the below code, r3 is used, so what value does it
> originally contain?
argv and argc are put on the userspace stack of program by kernel. (all the
nasty details are in fs/binfmt_elf.c...)
best regards,
p.
> Here is the objdump:
>
> 0100016c <_start>:
> 100016c: 9c 21 ff f8 l.addi r1,r1,0xfffffff8
> 1000170: d4 01 48 00 l.sw 0x0(r1),r9
> 1000174: d4 01 10 04 l.sw 0x4(r1),r2
> 1000178: 9c 41 00 08 l.addi r2,r1,0x8
> 100017c: a8 a3 00 00 l.ori r5,r3,0x0
> 1000180: 84 63 ff fc l.lwz r3,0xfffffffc(r3)
> 1000184: a8 85 00 00 l.ori r4,r5,0x0
> 1000188: b9 83 00 02 l.slli r12,r3,0x2
> 100018c: e0 a5 60 00 l.add r5,r5,r12
> 1000190: 04 00 00 15 l.jal 10001e4 <___uClibc_main>
> 1000194: 9c a5 00 04 l.addi r5,r5,0x4
> 1000198: 84 41 00 04 l.lwz r2,0x4(r1)
> 100019c: 85 21 00 00 l.lwz r9,0x0(r1)
> 10001a0: 44 00 48 00 l.jr r9
> 10001a4: 9c 21 00 08 l.addi r1,r1,0x8
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