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Message
From: Balaji V. Iyer<bviyer@n...>
Date: Wed May 4 02:23:41 CEST 2005
Subject: [openrisc] Starting Stack Value and arguments passing
So in the _start function I attached, previously (I am attaching it
again). The line that loads r3 with the address of r3-4 (I have indicated
it in the below code address 0x100080 , what exactly is contained in R3
during the start? I looked through the FS directory and the only place
where they have updated r3 is one function but it is #if to zero.
Thanks,
Balaji V. Iyer.
>> 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) <+++THIS LINE +++
>> 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
Matjaz Breskvar said:
> * 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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