asm_repl

A REPL for assembly.

Type some assembly instructions and immediatly see which registers were changed.

Currently only supports i386 and x86_64 on OS X.

Screenshot

Also see https://asciinema.org/a/19605.

Running

• Install radare2.
• make
• ./asm_repl (make run32 or make run64 to choose a specific architecture)

You need to codesign asm_repl binary or run it as root as we have to access the process we're running the assembly code in. You can codesign the binary so it can use task_for_pid without root by creating a certificate named task_for_pid using the guide here and then running make.

Commands

Valid input:
  Help:
    ?      - show this help
    ?[cmd] - show help for a command

  Commands:
    .set      - change value of register
    .read     - read from memory
    .write    - write hex to memory
    .writestr - write string to memory
    .alloc    - allocate memory
    .regs     - show the contents of the registers
    .show     - toggle shown register types

Any other input will be interpreted as x86_64 assembly

.set

Usage: .set register value
Changes the value of a register

  register - register name (GPR, FPR or status)
  value    - hex if GPR or FPR, 0 or 1 if status

.read

Usage: .read address [len]
Displays a hexdump of memory starting at address

  address - an integer or a register name
  len     - the amount of bytes to read

.write

Usage: .write address hexpairs
Writes hexpairs to a destination address

  address  - an integer or a register name
  hexpairs - pairs of hexadecimal numbers

.writestr

Usage: .writestr address string
Writes an ascii string to a destination address

  address - an integer or a register name
  string  - an ascii string

.alloc

Usage: .alloc len
Allocates some memory and returns the address

  len - the amount of bytes to allocate

.regs

Usage: .regs
Displays the values of the registers currently toggled on

.show

Usage: .show [gpr|status|fpr_hex|fpr_double]
Toggles which types of registers are shown

  gpr        - General purpose registers (rax, rsp, rip, ...)
  status     - Status registers (CF, ZF, ...)
  fpr_hex    - Floating point registers shown in hex (xmm0, xmm1, ...)
  fpr_double - Floating point registers shown as doubles

Todo

• Use a library (libr?) for assembling instead of reading the output of running rasm2.
• Support more architectures (arm).
• Support more platforms (linux).
• Arithmetic for commands (.read rip-0x10).
• Variables to specific memory addresses (.alloc 4 => .write $alloc 12345678).