Assembly Programming x86 Pentium Bug -


i'm having little problem in program written in assembly language x86 pentium. used debugger search abnormal thing in run of program. happening when try run in debugger goes when in terminal segmentation fault (core dumped) appears. know i'm accessing part of memory not defined see no problem on code.

here's code:

#.text #same .section .text .globl hell hell: push %ebp movl %esp, %ebp push %ebx #index push %edi push %esi subl $8, %esp movl 8(%ebp), %edx #str movl 12(%ebp), %eax #hist movl $-1, %esi xor %ecx, %ecx #j dec %ecx    forclean: inc %ecx cmp $26, %ecx je for1 movl $0, (%eax, %ecx, 4) jmp forclean  for1: inc %esi movb (%edx,%esi,1), %al cmpb $0, %al je fim cmpb $0x41, %al jl if2 cmpb $0x5a, %al jg if2 subb $0x41, %al movzbl %al, %ebx #mover para o index incl (%eax, %ebx, 4) jmp for1  if2: movb (%edx,%esi,1), %al cmpb $0x61, %al jl for1 cmpb $0x7a, %al jg for1 subb $0x61, %al movzbl %al, %ebx #mover para o index incl (%eax, %ebx, 4) jmp for1  end: movl %ebp, %esp popl %esi popl %edi popl %ebx popl %ebp ret

you store address of hist in eax, calculations character index inside al. since part of eax change address , that's why segmentation fault. clear ebx register @ beginning , use bl calculations instead.

also function's prolog , epilogue wrong. should be:

push %ebp movl %esp, %ebp subl $8, %esp    #space local variables push %ebx push %edi push %esi

and

popl %esi popl %edi popl %ebx movl %ebp, %esp popl %ebp

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