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I am writing power function in GNU Assembly x86 on Linux principal-neanderthal 6.8.0-41-generic x86_x64. When i launch i get "segmetantion fault (core dumped)" error.

.code32
.section .data

.section .text

.globl _start
_start:
  pushl $3
  pushl $2
  call power
  addl $8, %esp
  pushl %eax

  pushl $2
  pushl $5
  call power
  addl $8, %esp

  popl %ebx
  addl %eax, %ebx

  movl $1, %eax
  int $0x80

.type power, @function
power:
  pushl %ebp
  movl %esp, %ebp
  subl $4, %esp
  movl 8(%ebp), %ebx                   # HERE IS THE PROBLEM 
  movl 12(%ebp), %ecx
  movl %ebx, -4(%ebp)

power_loop_start:
  cmpl $1, %ecx
  je end_power
  movl -4(%ebp), %eax
  imull %ebx, %eax
  movl %eax, -4(%ebp) 
  decl %ecx
  jmp power_loop_start

end_power:
  movl -4(%ebp), %eax
  movl %ebp, %esp 
  popl %ebp 
  ret

After debugging in gbd found out that something is wrong in power function at 31 line when i try to load first argument in %ebx register. Also in gdb view %ebp, %eax, %ebx registers are replaced by their x64 variants with r suffix. Would be very thankful for explaining.

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  • 5
    How do you create the program? Have you used the proper options to produce 32 bit binary? Using gcc -m32 -nostdlib it works here and produces exit code 33 which I believe is the expected result. Commented Sep 10, 2024 at 17:26
  • 2
    @FischerBenkovscki Your program is written for 32-bit x86 mode but you assembled and run it as 64-bit x86_64. Commented Sep 11, 2024 at 10:00
  • 1
    If you want to use as and ld then do as --32 and ld -melf_i386 Commented Sep 11, 2024 at 10:52
  • 1
    @dimich Tell tale sign is the .code32 directive without which it wouldn't assemble with a 64 bit assembler. OP: do not specify this directive. If it seems to be required, you're using the wrong assembler! It merely masks the problem, but doesn't solve it. Use a 32 bit assembler for 32 bit code. Commented Sep 12, 2024 at 9:56
  • 1
    @Jester thank you very much. I was thinking that .code32 in the beginning is enough. You really helped me Commented Sep 13, 2024 at 17:55
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