Question

Yesterday I posted a question about my Recursive Fibonacci program in Assembly. I’m now getting the proper output, thanks to some help from the wonderful folks here, however immediately after the correct output is printed, my program crashes.

Here is the Sequence program that calls the Fibonacci program a given number of times (stored in L)

.386
.model Flat
public Sequence
extrn Fibonacci:proc
include iosmacros.inc
.code
Sequence proc
    MOV L, EAX
    XOR ECX, ECX ;start count at 0
    sequ:
    CMP ECX, L
        JA endseq ;if we have passed the given value (L), end
        putstr MsgOut1
        putint ECX ;number passed to Fibonacci
        putstr MsgOut2
        MOV count, ECX ;preserve count
        PUSH ECX
        CALL Fibonacci ;call Fibonacci
        putint ECX
        putch ' '
        MOV ECX, count ;restore count
        INC ECX ;increment the count
        JMP sequ ;again
    endseq:
        putint ecx
    ret
Sequence endp

.data
    MsgOut1 DB "Fib(", 0, 0 ;first half of output message
    MsgOut2 DB ") = ", 0, 0 ;second half of output message
    L DD, 0, 0 ;number of sequences to carry out
    count DD 0,0 ;for counting
end

And here is the code that calls the Sequence procedure:

.386
.model flat
extrn Sequence:proc
include Cs266.inc
.data
    Msg DB "Please input the number of sequences you would like carried out", 0Ah, 0 ;input request message
    err DB "reached end"

.code
include Rint.inc
    main:
        putstr Msg
        CALL Rint ;store int in EAX
        CALL Sequence
                putstr err
    ret

end

The Fibonacci code is as follows:

.386
.model Flat
public Fibonacci
include iosmacros.inc ;includes macros for outputting to the screen

.code
Fibonacci proc

    MOV ECX, [ESP+4]
    CMP ECX, 1
        JA Recurse
        MOV ECX, 1 ;return value in ECX
        JMP exit

Recurse:
    PUSH EBX ;preserve value of EBX
    DEC ECX
    PUSH ECX
    CALL Fibonacci
    MOV EBX, ECX ;EBX is preserved, so safe to use
    DEC [ESP] ;decrement the value already on the stack
    CALL Fibonacci
    ADD ECX, EBX ;return value in ECX
    ADD ESP, 4 ;remove value from stack
    POP EBX ;restore old value of EBX
exit:
ret
Fibonacci endp

.data
end

I’ve posted a bunch of code here, but it is just for your convenience in pointing me in the right direction. I BELIEVE the problem might be in Sequence, and my debugger does not help me.

EDIT: All I get in terms of an error is this:
https://i.stack.imgur.com/cqhcL.jpg
And if I do enable Visual Studio Just-In-Time debugging, it never helps.

Answer 1

Hmm…in your Fibonacci, I see two pushes and only one pop. At least at first glance, that seems like a little bit of a problem.