Question

I’m trying to compare 2 different char in assembly(calling assembly function in C program). One of the char belongs to a struct and the other is passed in when calling the function.

struct node {
    void   *previous;       
    void   *next;   
    unsigned int num;       
    unsigned int A;     
    unsigned int B;
}

node something;
something.A = 'C'; //assume everything else is correct

char A = 'C';
int func( char A ){ }:
find_course:
    pushl   %ebp
    movl    %esp, %ebp
    subl    $28, %esp
    movl    8(%ebp), %ebx
    movl    10(%ebp), %ecx
    movl    16(%ebp), %edx
    movl    something, %edi
    cmpl    10(%edi), %ebx

.END:
    leave
    ret

when I debug with gdb, %ebx is 83 whereas 10(%edi) is 21315. If I print them out as characters, both appear to be ‘C’. Is there any way that I can convert 21315 to 83?

Answer 1

Yes: you want to use movb 10(%edi), %al instead.