opcode

rabbit hole

~

~

When you really just
want to know
what hides beneath
movl $1, %ecx

~

opcode

opcode() {
    if [[ "$1" == "" ]]; then
        echo "together:"
        echo "usage: opcode 'mov \$1, %eax'"
        echo "usage: opcode 'mov \$1, %eax; inc %eax'"
        
        echo ""
        echo "one-at-a-time:"
        echo "usage: opcode_series 'mov \$1, %eax; inc %eax'"
    else
        local n="$(mktemp)"
        local assembly_fn="$n.s"
        local object_fn="$n.o"
        asm="$*"
        echo "  $asm"
        echo -e ".section .text\n$asm" > "$assembly_fn" && as -msyntax=att "$assembly_fn" -o "$object_fn" && readelf --hex-dump=.text "$object_fn" | tail -n +3
        rm -f "$assembly_fn" "$object_fn"
    fi
}

opcode_series

opcode_series() {
    if [[ "$1" == "" ]]; then
        echo "one-at-a-time:"
        echo "usage: opcode_series 'mov \$1, %eax; inc %eax'"
        
        echo ""
        echo "together:"
        echo "usage: opcode 'mov \$1, %eax'"
        echo "usage: opcode 'mov \$1, %eax; inc %eax'"
    else
        IFS=$';' read -r -a lines <<< "$*"
        for line in "${lines[@]}"; do
            line="${line#"${line%%[![:space:]]*}"}" # remove leading spaces
            opcode "$line"
        done
    fi
}

Test Area

It can be handy to have this little test script for messing around with them.

test_opcode.sh

#!/bin/bash

echo "----------------------------------------"
echo "test opcode generation - all together" 
echo "----------------------------------------"

opcode() {
    if [[ "$1" == "" ]]; then
        echo "together:"
        echo "usage: opcode 'mov \$1, %eax'"
        echo "usage: opcode 'mov \$1, %eax; inc %eax'"
        
        echo ""
        echo "one-at-a-time:"
        echo "usage: opcode_series 'mov \$1, %eax; inc %eax'"
    else
        local n="$(mktemp)"
        local assembly_fn="$n.s"
        local object_fn="$n.o"
        asm="$*"
        echo "  $asm"
        echo -e ".section .text\n$asm" > "$assembly_fn" && as -msyntax=att "$assembly_fn" -o "$object_fn" && readelf --hex-dump=.text "$object_fn" | tail -n +3
        rm -f "$assembly_fn" "$object_fn"
    fi
}

opcode 'movl $1, %eax'
opcode 'mov $1, %eax; inc %eax'

echo "----------------------------------------"
echo "test opcode generation - one-at-a-time" 
echo "----------------------------------------"

opcode_series() {
    if [[ "$1" == "" ]]; then
        echo "one-at-a-time:"
        echo "usage: opcode_series 'mov \$1, %eax; inc %eax'"
        
        echo ""
        echo "together:"
        echo "usage: opcode 'mov \$1, %eax'"
        echo "usage: opcode 'mov \$1, %eax; inc %eax'"
    else
        IFS=$';' read -r -a lines <<< "$*"
        for line in "${lines[@]}"; do
            line="${line#"${line%%[![:space:]]*}"}" # remove leading spaces
            opcode "$line"
        done
    fi
}

opcode_series 'mov $1, %eax; inc %eax'

Output of Test

What pops out before you start messing with it :)

bo@pop:~/dev/bin/test$ test_opcode.sh 
----------------------------------------
test opcode generation - all together
----------------------------------------
  movl $1, %eax
  0x00000000 b8010000 00                         .....

  mov $1, %eax; inc %eax
  0x00000000 b8010000 00ffc0                     .......

----------------------------------------
test opcode generation - one-at-a-time
----------------------------------------
  mov $1, %eax
  0x00000000 b8010000 00                         .....

  inc %eax
  0x00000000 ffc0                                ..