152 lines
2.1 KiB
ArmAsm
152 lines
2.1 KiB
ArmAsm
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.globl _argv
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.data
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.align 4
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.comm argstr,256,4
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_argv: .long 0
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.text
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.globl start
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start:
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# clear bss (could be done better)
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# is it actually necessary?
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mov $__bss,%eax
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1:
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movb $0,(%eax)
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inc %eax
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cmp $__ebss,%eax
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jbe 1b
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# copy command line args (can't use them directly, not aligned)
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mov %esp,%eax
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shr $2,%eax
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mov %eax,_argv
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mov (%esp),%ecx # number of arguments
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mov $argstr,%edi
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1:
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mov (%esp,%ecx,4),%esi
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mov %edi,%eax
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shr $2,%eax
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mov %eax,(%esp,%ecx,4)
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call cpystr
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loop 1b
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call bsymbs
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mov _main,%eax
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shl $2,%eax
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call *%eax
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mov %eax,%ebx
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mov $1,%eax
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int $0x80
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# copy string from esi to edi and convert '\0' to B's '*e', align edi
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cpystr:
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mov (%esi),%al
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test %al,%al
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jz 1f
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mov %al,(%edi)
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inc %edi
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inc %esi
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jmp cpystr
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1:
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movb $04,(%edi)
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inc %edi
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add $3,%edi
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and $~3,%edi
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ret
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# shift addresses filled in by the linker 2 bits to the right
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# so B only ever sees word addresses
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bsymbs:
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mov $__bsymb,%eax
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1:
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cmp $__ebsymb,%eax
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jge 1f
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mov (%eax),%ebx
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mov (%ebx),%ecx
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shr $2,%ecx
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mov %ecx,(%ebx)
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add $4,%eax
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jmp 1b
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1:
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ret
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.globl retrn
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retrn:
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mov %ebp,%esp
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pop %ebp
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ret
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# handle switch table:
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# eax has the value, ebx the address of the switch table
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.globl bswitch
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bswitch:
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xor %ecx,%ecx
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1:
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mov (%ebx,%ecx,8),%edx
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mov 4(%ebx,%ecx,8),%edi
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test %edi,%edi
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jz 1f # default (last in table)
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cmp %eax,%edx
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je 2f
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inc %ecx
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jmp 1b
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1:
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jmp *%edx
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2:
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jmp *%edi
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#
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# Library functions in assembly
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#
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.globl _exit
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.data
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.align 4
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.section .bsymb; .long _exit; .data
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_exit: .long 1f
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.text
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.align 4
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1: mov $1,%eax
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mov $0,%ebx
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int $0x80
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.globl _write
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.data
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.align 4
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.section .bsymb; .long _write; .data
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_write: .long 1f
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.text
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.align 4
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1: mov 4(%esp),%ebx
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mov 8(%esp),%ecx
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shl $2,%ecx
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mov 12(%esp),%edx
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mov $4,%eax
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int $0x80
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ret
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.globl _read
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.data
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.align 4
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.section .bsymb; .long _read; .data
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_read: .long 1f
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.text
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.align 4
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1: mov 4(%esp),%ebx
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mov 8(%esp),%ecx
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shl $2,%ecx
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mov 12(%esp),%edx
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mov $3,%eax
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int $0x80
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ret
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.globl _inv
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.data
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.align 4
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.section .bsymb; .long _inv; .data
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_inv: .long 1f
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.text
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.align 4
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1: mov 4(%esp),%eax
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not %eax
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ret
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