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So in the _start function I attached, previously (I am attaching it

* Balaji V. Iyer (bviyer@n...) wrote:
> 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.

Sorry, i don't remember anymore... what i'd suggest you do is just run linux
in the simulator and capture starting up of a program to execlog. there it
will be probably obvious what are the values, and if you can't deduce the
reasoning behind them or where they're set up, you can still trace them
back to their origin.

best regards,
p.

> 
> 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
> > _______________________________________________
> > http://www.opencores.org/mailman/listinfo/openrisc
> >
> 
> 
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