I installed Qtspim to try out some MIPS commands. I've written a few text files, saved with a ".asm" extension, with some commands. Here's one:
.text
.globl main
main:
addi $t0, $zero, 3
addi $t1, $zero, 5
add $t2, $t0, $t1
li $v0, 10
syscall
However, when I try the "Reinitialize and Load File" command in Qtspim, the text that shows up in the "text" section of the program does not correspond to my text file. My code is in the middle of it, but with a bunch of EXTRA code that wasn't in my file. Why is this? Am I loading it wrong somehow? What's all this other code?
User Text Segment [00400000]..[00440000]
[00400000] 8fa40000 lw $4, 0($29) ; 183: lw $a0 0($sp) # argc
[00400004] 27a50004 addiu $5, $29, 4 ; 184: addiu $a1 $sp 4 # argv
[00400008] 24a60004 addiu $6, $5, 4 ; 185: addiu $a2 $a1 4 # envp
[0040000c] 00041080 sll $2, $4, 2 ; 186: sll $v0 $a0 2
[00400010] 00c23021 addu $6, $6, $2 ; 187: addu $a2 $a2 $v0
[00400014] 0c100009 jal 0x00400024 [main] ; 188: jal main
[00400018] 00000000 nop ; 189: nop
[0040001c] 3402000a ori $2, $0, 10 ; 191: li $v0 10
[00400020] 0000000c syscall ; 192: syscall # syscall 10 (exit)
[00400024] 20080003 addi $8, $0, 3 ; 2: addi $t0, $zero, 3
[00400028] 20090005 addi $9, $0, 5 ; 3: addi $t1, $zero, 5
[0040002c] 01095020 add $10, $8, $9 ; 4: add $t2, $t0, $t1
[00400030] 3402000a ori $2, $0, 10 ; 5: li $v0, 10
[00400034] 0000000c syscall ; 6: syscall
Kernel Text Segment [80000000]..[80010000]
[80000180] 0001d821 addu $27, $0, $1 ; 90: move $k1 $at # Save $at
[80000184] 3c019000 lui $1, -28672 ; 92: sw $v0 s1 # Not re-entrant and we can't trust $sp
[80000188] ac220200 sw $2, 512($1)
[8000018c] 3c019000 lui $1, -28672 ; 93: sw $a0 s2 # But we need to use these registers
[80000190] ac240204 sw $4, 516($1)
[80000194] 401a6800 mfc0 $26, $13 ; 95: mfc0 $k0 $13 # Cause register
[80000198] 001a2082 srl $4, $26, 2 ; 96: srl $a0 $k0 2 # Extract ExcCode Field
[8000019c] 3084001f andi $4, $4, 31 ; 97: andi $a0 $a0 0x1f
[800001a0] 34020004 ori $2, $0, 4 ; 101: li $v0 4 # syscall 4 (print_str)
[800001a4] 3c049000 lui $4, -28672 [__m1_] ; 102: la $a0 __m1_
[800001a8] 0000000c syscall ; 103: syscall
[800001ac] 34020001 ori $2, $0, 1 ; 105: li $v0 1 # syscall 1 (print_int)
[800001b0] 001a2082 srl $4, $26, 2 ; 106: srl $a0 $k0 2 # Extract ExcCode Field
[800001b4] 3084001f andi $4, $4, 31 ; 107: andi $a0 $a0 0x1f
[800001b8] 0000000c syscall ; 108: syscall
[800001bc] 34020004 ori $2, $0, 4 ; 110: li $v0 4 # syscall 4 (print_str)
[800001c0] 3344003c andi $4, $26, 60 ; 111: andi $a0 $k0 0x3c
[800001c4] 3c019000 lui $1, -28672 ; 112: lw $a0 __excp($a0)
[800001c8] 00240821 addu $1, $1, $4
[800001cc] 8c240180 lw $4, 384($1)
[800001d0] 00000000 nop ; 113: nop
[800001d4] 0000000c syscall ; 114: syscall
[800001d8] 34010018 ori $1, $0, 24 ; 116: bne $k0 0x18 ok_pc # Bad PC exception requires special checks
[800001dc] 143a0008 bne $1, $26, 32 [ok_pc-0x800001dc]
[800001e0] 00000000 nop ; 117: nop
[800001e4] 40047000 mfc0 $4, $14 ; 119: mfc0 $a0 $14 # EPC
[800001e8] 30840003 andi $4, $4, 3 ; 120: andi $a0 $a0 0x3 # Is EPC word-aligned?
[800001ec] 10040004 beq $0, $4, 16 [ok_pc-0x800001ec]
[800001f0] 00000000 nop ; 122: nop
[800001f4] 3402000a ori $2, $0, 10 ; 124: li $v0 10 # Exit on really bad PC
[800001f8] 0000000c syscall ; 125: syscall
[800001fc] 34020004 ori $2, $0, 4 ; 128: li $v0 4 # syscall 4 (print_str)
[80000200] 3c019000 lui $1, -28672 [__m2_] ; 129: la $a0 __m2_
[80000204] 3424000d ori $4, $1, 13 [__m2_]
[80000208] 0000000c syscall ; 130: syscall
[8000020c] 001a2082 srl $4, $26, 2 ; 132: srl $a0 $k0 2 # Extract ExcCode Field
[80000210] 3084001f andi $4, $4, 31 ; 133: andi $a0 $a0 0x1f
[80000214] 14040002 bne $0, $4, 8 [ret-0x80000214]; 134: bne $a0 0 ret # 0 means exception was an interrupt
[80000218] 00000000 nop ; 135: nop
[8000021c] 401a7000 mfc0 $26, $14 ; 145: mfc0 $k0 $14 # Bump EPC register
[80000220] 275a0004 addiu $26, $26, 4 ; 146: addiu $k0 $k0 4 # Skip faulting instruction
[80000224] 409a7000 mtc0 $26, $14 ; 148: mtc0 $k0 $14
[80000228] 3c019000 lui $1, -28672 ; 153: lw $v0 s1 # Restore other registers
[8000022c] 8c220200 lw $2, 512($1)
[80000230] 3c019000 lui $1, -28672 ; 154: lw $a0 s2
[80000234] 8c240204 lw $4, 516($1)
[80000238] 001b0821 addu $1, $0, $27 ; 157: move $at $k1 # Restore $at
[8000023c] 40806800 mtc0 $0, $13 ; 160: mtc0 $0 $13 # Clear Cause register
[80000240] 401a6000 mfc0 $26, $12 ; 162: mfc0 $k0 $12 # Set Status register
[80000244] 375a0001 ori $26, $26, 1 ; 163: ori $k0 0x1 # Interrupts enabled
[80000248] 409a6000 mtc0 $26, $12 ; 164: mtc0 $k0 $12
[8000024c] 42000018 eret ; 167: eret