CODEWITHSUNDEEP
functionassemblyx86nasm
Iszlai Lehel
Iszlai Lehel

Reputation: 231

After executing this nasm function main doesn't continue. It exits without errors

I call the function the following way from main:

 main:
;memory alocation ect
call    encode

The encode function looks like this: It does a simple RLE algorithm.

encode:
;IN eax - pointer a memoria elejere
;IN ecx - sor hossza
;OUT eax -pointer az eredmeny elejere
;OUt ecx -a kiirt sor hossza
;elso char

Here it reads the first characer

;push eax
push ebp
xor ebp,ebp
push esi
push edi
push eax
xor edi,edi

Here it allocates memory:

;lefoglal memoria eredmenynek
mov ebx,eax
mov eax,ecx
call mem_alloc
;esi legyen eredmeny memoria kezdete
mov esi,eax
mov eax,ebx
;eax ismet a memoria poiter

xor edx,edx
mov dl,[eax]
; push eax
; xor eax,eax
; mov al,dl
; call io_writeint
; call mio_writeln
; pop eax

;lastChar az elso char
mov [lastChar],dl

The main loop the loops to the "vector"

inc ebp 
;dec ecx
.goloop:
mov dl,[eax+ebp]
xor ebx,ebx
mov bl,[lastChar]
cmp dl,bl
jne .newChar
xor ebx,ebx
mov bl,[count]
inc bl
mov [count],bl


.backloop:
loop .goloop

.newChar:

mov [esi+edi],bl
inc edi
mov byte[esi+edi],-1
inc edi
mov bl,[count]
mov [esi+edi],bl
inc edi
mov byte[count],0
cmp ecx,0
ja .backloop

.veg:
mov ebx,esi
mov edx,edi 
pop edi
pop esi
pop eax

pop ebp
pop eax
mov eax,ebx
mov ecx,edx 

ret

Upvotes: 0

Views: 242

Answers (1)

phillid
phillid

Reputation: 198

It appears that you push four registers onto the stack but pop five off.

When you CALL an address, the instruction pointer is pushed onto the stack, then the processor JMPs to the label/address you specify. When RET is executed, it POPs off the stack and jumps to the address that it popped off. RET expects that the address that CALL pushed onto the stack will be the next word in the stack, but you have already popped this byte off when you popped more registers than you pushed.

You could try taking the very last

push eax

out of your code.

Upvotes: 1

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