#disassembly #disassembler

app yaxpeax-eval

batch eval tool for machine code

1 unstable release

0.0.1 Dec 31, 2022

#16 in #disassembly

0BSD license

347 lines



yaxpeax-eval is the repo providing yaxeval, a tool to execute machine code with preconditions and report state at exit.

currently, yaxeval works by spawning a thread and executing the provided machine code on the local physical processor. there is some boring glue for architecture-dependent state setting and reporting. this means that yaxeval supports, or is close to supporting, whatever physical processor you would run it on.

i am interested in using qemu-user as an alternate execution backend for cross-platform emulation. yaxeval should be able to use qemu-user just the same for setup and reporting by using qemu's gdbserver.


if you just want to build and use it, cargo install yaxpeax-eval should get you started. otherwise, clone this repo and a cargo build will work as well. yaxeval <x86 machine code> is a good starting point:

yaxpeax-eval> ./target/release/yaxeval b878563412
loaded code...
  00007f774b497000: mov eax, 0x12345678
  00007f774b497005: 🏁 (int 0x3)
  rax:   0000000000000000
   to -> 0000000012345678
  rip:   00007f774b497000
   to -> 00007f774b497006

initial register state is generally zeroes, with exception of rip, which by default points to whatever address an unrestricted mmap could find.

inital register values, including rip, can be specified explicitly:

yaxpeax-eval> ./target/release/yaxeval --regs rax=4,rcx=5,rip=0x123456789a,eflags=0x246 03c133c9
loaded code...
  000000123456789a: add eax, ecx
  000000123456789c: xor ecx, ecx
  000000123456789e: 🏁 (int 0x3)
  rax:   0000000000000004
   to -> 0000000000000009
  rcx:   0000000000000005
   to -> 0000000000000000
  rip:   000000123456789a
   to -> 000000123456789f

and if the provided code disastrously crashes, yaxeval will try to say a bit about what occurred:

yaxpeax-eval> ./target/release/yaxeval --regs rax=4,rcx=5,rip=0x123456789a,eflags=0x246 0000
loaded code...
  000000123456789a: add byte [rax], al
  000000123456789c: 🏁 (int 0x3)
  eflags:        00000246
   to ->         00010246
sigsegv at unexpected address: 000000123456789a


  • accept some config to map memory regions other than the implicitly-initialized code region
  • machine-friendly input/output formats
  • mode to single-step through provided code?


~196K SLoC