Rappel is a pretty janky assembly REPL. It works by creating a shell ELF, starting it under ptrace, then continiously rewriting/running the .text section, while showing the register states. It's maybe half done right now, and supports Linux x86, amd64, and armv7 (no thumb) at the moment.
The only dependencies are libedit an asembler (nasm on x86/amd64, as on ARM) , which on debian can be installed with the libedit-dev and nasm/binutils packages.
$ CC=clang make
It should work fine with gcc, albiet with a few more warnings.
By default rappel is compiled with your native architecture. If you're on amd64 and want to target x86 you can do this with
$ ARCH=i386 CC=clang make
In theory you can also compile an armv7 binary this way, but I really doubt it will work. For rappel to function, the architecture of the main rappel binary must match that of the process it creates, and the host must be able to run binaries of this architecture.
Rappel has two modes it can operate in. A pipe mode for one off things, a la
$ echo "inc eax" | bin/rappel
rax:0x0000000000000001 rbx:0x0000000000000000 rcx:0x0000000000000000 rdx:0x0000000000000000
rsi:0x0000000000000000 rdi:0x0000000000000000 r8 :0x0000000000000000 r9 :0x0000000000000000
r10:0x0000000000000000 r11:0x0000000000000000 r12:0x0000000000000000 r13:0x0000000000000000
r14:0x0000000000000000 r15:0x0000000000000000
rip:0x0000000000400003 rsp:0x00007fffffffee80 rbp:0x0000000000000000
flags:0x0000000000000202 [CF: 0, ZF: 0, OF: 0, SF: 0, PF: 0, AF: 0]
$
Or an interactive mode:
$ bin/rappel
rax:0x0000000000000000 rbx:0x0000000000000000 rcx:0x0000000000000000 rdx:0x0000000000000000
rsi:0x0000000000000000 rdi:0x0000000000000000 r8 :0x0000000000000000 r9 :0x0000000000000000
r10:0x0000000000000000 r11:0x0000000000000000 r12:0x0000000000000000 r13:0x0000000000000000
r14:0x0000000000000000 r15:0x0000000000000000
rip:0x0000000000400001 rsp:0x00007fffffffee80 rbp:0x0000000000000000
flags:0x0000000000000202 [CF: 0, ZF: 0, OF: 0, SF: 0, PF: 0, AF: 0]
> inc rax
rax:0x0000000000000001 rbx:0x0000000000000000 rcx:0x0000000000000000 rdx:0x0000000000000000
rsi:0x0000000000000000 rdi:0x0000000000000000 r8 :0x0000000000000000 r9 :0x0000000000000000
r10:0x0000000000000000 r11:0x0000000000000000 r12:0x0000000000000000 r13:0x0000000000000000
r14:0x0000000000000000 r15:0x0000000000000000
rip:0x0000000000400004 rsp:0x00007fffffffee80 rbp:0x0000000000000000
flags:0x0000000000000202 [CF: 0, ZF: 0, OF: 0, SF: 0, PF: 0, AF: 0]
> push rax
rax:0x0000000000000001 rbx:0x0000000000000000 rcx:0x0000000000000000 rdx:0x0000000000000000
rsi:0x0000000000000000 rdi:0x0000000000000000 r8 :0x0000000000000000 r9 :0x0000000000000000
r10:0x0000000000000000 r11:0x0000000000000000 r12:0x0000000000000000 r13:0x0000000000000000
r14:0x0000000000000000 r15:0x0000000000000000
rip:0x0000000000400002 rsp:0x00007fffffffee78 rbp:0x0000000000000000
flags:0x0000000000000202 [CF: 0, ZF: 0, OF: 0, SF: 0, PF: 0, AF: 0]
> pop rbx
rax:0x0000000000000001 rbx:0x0000000000000001 rcx:0x0000000000000000 rdx:0x0000000000000000
rsi:0x0000000000000000 rdi:0x0000000000000000 r8 :0x0000000000000000 r9 :0x0000000000000000
r10:0x0000000000000000 r11:0x0000000000000000 r12:0x0000000000000000 r13:0x0000000000000000
r14:0x0000000000000000 r15:0x0000000000000000
rip:0x0000000000400002 rsp:0x00007fffffffee80 rbp:0x0000000000000000
flags:0x0000000000000202 [CF: 0, ZF: 0, OF: 0, SF: 0, PF: 0, AF: 0]
> cmp rax, rbx
rax:0x0000000000000001 rbx:0x0000000000000001 rcx:0x0000000000000000 rdx:0x0000000000000000
rsi:0x0000000000000000 rdi:0x0000000000000000 r8 :0x0000000000000000 r9 :0x0000000000000000
r10:0x0000000000000000 r11:0x0000000000000000 r12:0x0000000000000000 r13:0x0000000000000000
r14:0x0000000000000000 r15:0x0000000000000000
rip:0x0000000000400004 rsp:0x00007fffffffee80 rbp:0x0000000000000000
flags:0x0000000000000246 [CF: 0, ZF: 1, OF: 0, SF: 0, PF: 0, AF: 0]
> ^D
$
x86 looks like:
$ echo "nop" | bin/rappel
eax:0x00000000 ebx:0x00000000 ecx:0x00000000 edx:0x00000000
esi:0x00000000 edi:0x00000000
eip:0x00400002 esp:0xffffdf10 ebp:0x00000000
flags:0x00000202 [CF: 0, ZF: 0, OF: 0, SF: 0, PF: 0, AF: 0]
$
ARM looks like:
$ echo "nop" | bin/rappel
R0 :0x00000000 R1 :0x00000000 R2 :0x00000000 R3 :0x00000000
R4 :0x00000000 R5 :0x00000000 R6 :0x00000000 R7 :0x00000000
R8 :0x00000000 R9 :0x00000000 R10:0x00000000
FP :0x00000000 IP :0x00000000
SP :0xbe927f30 LR :0x00000000 PC :0x00400004
APSR:0x00000010
$
Someone asked about xmm registers. If you pass -x it will dump out quite a bit of info.
> inc rax
GP Regs:
rax: 0x0000000000000001 rbx: 0x0000000000000000 rcx: 0x0000000000000000 rdx: 0x0000000000000000
rsi: 0x0000000000000000 rdi: 0x0000000000000000 r8 : 0x0000000000000000 r9 : 0x0000000000000000
r10: 0x0000000000000000 r11: 0x0000000000000000 r12: 0x0000000000000000 r13: 0x0000000000000000
r14: 0x0000000000000000 r15: 0x0000000000000000
cs: 0x0000000000000033 ss: 0x000000000000002b ds: 0x0000000000000000
es: 0x0000000000000000 fs: 0x0000000000000000 gs: 0x0000000000000000
rip: 0x0000000000400004 rsp: 0x00007fffffffee80 rbp: 0x0000000000000000
flags: 0x0000000000000202 [cf:0, zf:0, of:0, sf:0, pf:0, af:0]
FP Regs:
rip: 0x0000000000000000 rdp: 0x0000000000000000 mxcsr: 0x00001f80 mxcsr_mask:0x00000000
cwd: 0x037f swd: 0x0000 ftw: 0x0000 fop: 0x0000
st_space:
0x00: 0x00000000 0x00000000 0x00000000 0x00000000
0x10: 0x00000000 0x00000000 0x00000000 0x00000000
0x20: 0x00000000 0x00000000 0x00000000 0x00000000
0x30: 0x00000000 0x00000000 0x00000000 0x00000000
0x40: 0x00000000 0x00000000 0x00000000 0x00000000
0x50: 0x00000000 0x00000000 0x00000000 0x00000000
0x60: 0x00000000 0x00000000 0x00000000 0x00000000
0x70: 0x00000000 0x00000000 0x00000000 0x00000000
xmm_space:
0x00: 0x00000000 0x00000000 0x00000000 0x00000000
0x10: 0x00000000 0x00000000 0x00000000 0x00000000
0x20: 0x00000000 0x00000000 0x00000000 0x00000000
0x30: 0x00000000 0x00000000 0x00000000 0x00000000
0x40: 0x00000000 0x00000000 0x00000000 0x00000000
0x50: 0x00000000 0x00000000 0x00000000 0x00000000
0x60: 0x00000000 0x00000000 0x00000000 0x00000000
0x70: 0x00000000 0x00000000 0x00000000 0x00000000
0x80: 0x00000000 0x00000000 0x00000000 0x00000000
0x90: 0x00000000 0x00000000 0x00000000 0x00000000
0xa0: 0x00000000 0x00000000 0x00000000 0x00000000
0xb0: 0x00000000 0x00000000 0x00000000 0x00000000
0xc0: 0x00000000 0x00000000 0x00000000 0x00000000
0xd0: 0x00000000 0x00000000 0x00000000 0x00000000
0xe0: 0x00000000 0x00000000 0x00000000 0x00000000
0xf0: 0x00000000 0x00000000 0x00000000 0x00000000
There are some other regsets the kernel exports via ptrace(), but they're dependent on kernel version, and didn't want to try to detect and adjust at runtime. If you want them, you should just need to add the storage in proc_info_t, edit _collect_regs(), then add the display in the relevant display function.
Right now platforms are largely determined by what hardware I own. I plan on splitting it apart a bit more in the future to make adding new archs easier.
You can get pretty much all the documentation with either -h from the command line, or .help from the interactive bit.