hi all,
total noob here with assembly. I'm working on a project for one my classes and for some reason we all keep getting segmentation faults when attempting to run the program.
I can't for the life of me figure out what the heck is going on and why this keep happening. I have tried to go though the program and remove things little by little to see if I could find the cancerous lines but I was unable.. As a last resort I've come to Daniweb to see if anyone can spot it for me... (My instructor was not able to...)
.section .data
Sregs:
.long 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15
OPtbl:
.long meth_exit
.long meth_nim
.long meth_nim
.long meth_nim
.long meth_ldr
.long meth_ldri
.long meth_ldrm
.long meth_ldrt
.rept 256-((. - OPtbl)/4)
.long meth_nim
.endr
Smem:
.byte 0x04, 0x33, 0x30
.section .text
.globl _start
_start:
movl $0, %edi
loop_fetch:
movb Smem(,%edi,1),%al
#//And the OP code in %eax with
#//dec(255) or bin(11111111)
#//This clears any garbage left
#//in the top portion of register eax
andl $0xff,%eax
#//Now that %eax is clean and we have
#//our OP code we will move the instructions
#//for that operation into register %eax
#//killing the OP code but we have the instructions
#//for that OP code instead now
movl OPtbl(,%eax,4),%eax
#//increment %edi to the next memory location
incl %edi
#//call the operation code we put
#//into %eax register.
call *%eax
#//Jump to beginning of the loop
#//and repeat the process
jmp loop_fetch
#//END OF loop_fetch
#//Begin not implemented method
meth_nim:
#//Increment register edi to move to the
#//next memory location
incl %edi
#//Return to the call location
ret
#//End nim method
#//Begin loader method
meth_ldr:
#//Get next byte in Smem
#//which contains the Rd
#//mov Rd to %eax
movb Smem(,%edi,1),%al
#//[%eax] = | 0000 0000 | 0000 0000 | 0000 0000| 0011 0011 | // hex: 33
#//Convert from string "3" to int 3
#//by anding off the first 3 in hex 33
andl $0x0f,%eax #//1 f saves 4bits
#//[%eax] = | 0000 0000 | 0000 0000 | 0000 0000| 0011 0011 | // hex: 33
#//[andl] = | 0000 0000 | 0000 0000 | 0000 0000| 0000 1111 | // hex: 0F
#// ----------------------------------------------------------------
#//[%eax] = | 0000 0000 | 0000 0000 | 0000 0000| 0000 0011 | // hex: 03
#//^Now we have Rd
#//Inc index to next byte of Smem
incl %edi
//Get the data from Smem and place
#//it into %ebx
movb Smem(%edi), %bl
#//Convert from string to int
andl $0x0f, %ebx
#//^Now we have both Rd & Rs
#//[%eax] = Rd
#//[%ebx] = Rs
#//Get whats in the Sregs[Rs]
#//store it in %ebx
movl Sregs(%ebx), %ebx
#//Now move it from %ebx into
#//Sregs[Rd]
movl %ebx, Sregs(%eax)
#//Increment %edi to point to
#//next byte of Smem
incl %edi
#//Return to the call location
ret
#//End loader method
#//Begin loader i method[Rd,$i]
meth_ldri:
#//Get next byte in Smem
#//which contains the Rd
#//mov Rd to %eax
movb Smem(, %edi,1), %al
#//[%eax] = | 0000 0000 | 0000 0000 | 0000 0000| 00011 0011 | // hex: 33
#//Convert from string "3" to int 3
#//by anding off the first 3 in hex 33
andl $0x0f, %eax #//1 f saves 4bits
#//[%eax] = | 0000 0000 | 0000 0000 | 0000 0000| 0011 0011 | // hex: 33
#//[andl] = | 0000 0000 | 0000 0000 | 0000 0000| 0000 1111 | // hex: 0F
#// ----------------------------------------------------------------
#//[%eax] = | 0000 0000 | 0000 0000 | 0000 0000| 0000 0011 | // hex: 03
#//^Now we have Rd
#//Increment %edi to get next
#//byte of Smem
incl %edi
#//Get the $i value and place
#//it into %ebx
movb Smem(%edi), %bl
#//Clean off high end of %ebx
#//No conversion here; saving whole byte
andl $0xff, %ebx
#//^Now we have both Rd & $i
#//[%eax] = Rd
#//[%ebx] = $i
#//Place the $i value into Sregs[Rd]
movl %ebx, Sregs(%eax)
#//Increment the index to the next byte
#//of Smem
incl %edi
#//Return to the call location
ret
#//End loader i method
#//Begin loader m method
meth_ldrm:
jmp meth_nim
#//End loader m method
#//Begin loader t method
meth_ldrt:
jmp meth_nim
#//End loader t method
meth_exit:
movl $1, %ebx
movl $42, %ebx
int $0x80Thanks all for your suggestions/tips..
~eff