Context exceptions with ARM target

[mat-pr]

Description

Vaguely similar to #1097.
When debugging an ARM target with qemu-system-arm, the context command fails to execute with the following backtraces:

'context': Print out the current register, instruction, and stack context.
Traceback (most recent call last):
  File "/home/m/Desktop/pwndbg/pwndbg/commands/__init__.py", line 197, in __call__
    return self.function(*args, **kwargs)
  File "/home/m/Desktop/pwndbg/pwndbg/commands/__init__.py", line 357, in _OnlyWhenRunning
    return function(*a, **kw)
  File "/home/m/Desktop/pwndbg/pwndbg/commands/context.py", line 406, in context
    func(
  File "/home/m/Desktop/pwndbg/pwndbg/commands/context.py", line 514, in context_regs
    regs = get_regs()
  File "/home/m/Desktop/pwndbg/pwndbg/commands/context.py", line 606, in get_regs
    desc = pwndbg.chain.format(value)
  File "/home/m/Desktop/pwndbg/pwndbg/chain.py", line 174, in format
    enhanced = pwndbg.enhance.enhance(
  File "/home/m/Desktop/pwndbg/pwndbg/enhance.py", line 119, in enhance
    pwndbg_instr = pwndbg.disasm.one(value, enhance=False)
  File "/home/m/Desktop/pwndbg/pwndbg/disasm/__init__.py", line 244, in one
    for insn in get(address, 1, emu, enhance=enhance, from_cache=from_cache, put_cache=put_cache):
  File "/home/m/Desktop/pwndbg/pwndbg/disasm/__init__.py", line 278, in get
    i = get_one_instruction(
  File "/home/m/Desktop/pwndbg/pwndbg/disasm/__init__.py", line 211, in get_one_instruction
    md = get_disassembler(address)
  File "/home/m/Desktop/pwndbg/pwndbg/disasm/__init__.py", line 161, in get_disassembler
    extra = CS_MODE_THUMB if (pwndbg.gdblib.regs.cpsr & (1 << 5)) else CS_MODE_ARM
TypeError: unsupported operand type(s) for &: 'NoneType' and 'int'

and

'context': Print out the current register, instruction, and stack context.
Traceback (most recent call last):
  File "/home/m/Desktop/pwndbg/pwndbg/commands/__init__.py", line 197, in __call__
    return self.function(*args, **kwargs)
  File "/home/m/Desktop/pwndbg/pwndbg/commands/__init__.py", line 357, in _OnlyWhenRunning
    return function(*a, **kw)
  File "/home/m/Desktop/pwndbg/pwndbg/commands/context.py", line 406, in context
    func(
  File "/home/m/Desktop/pwndbg/pwndbg/commands/context.py", line 635, in context_disasm
    result = pwndbg.gdblib.nearpc.nearpc(
  File "/home/m/Desktop/pwndbg/pwndbg/gdblib/nearpc.py", line 129, in nearpc
    instructions, index_of_pc = pwndbg.disasm.near(
  File "/home/m/Desktop/pwndbg/pwndbg/disasm/__init__.py", line 349, in near
    emu = pwndbg.emu.emulator.Emulator()
  File "/home/m/Desktop/pwndbg/pwndbg/emu/emulator.py", line 194, in __init__
    self.uc_mode = self.get_uc_mode()
  File "/home/m/Desktop/pwndbg/pwndbg/emu/emulator.py", line 544, in get_uc_mode
    mode |= U.UC_MODE_THUMB if (pwndbg.gdblib.regs.cpsr & (1 << 5)) else U.UC_MODE_ARM
TypeError: unsupported operand type(s) for &: 'NoneType' and 'int'

Patching the two reported lines in pwndbg/pwndbg/disasm/__init__.py and pwndbg/pwndbg/emu/emulator.py, the debugging process seems reasonable.

Steps to reproduce

I ran gdb-multiarch on the ARM binary. Then the first exception is triggered with

set exception-verbose on
target remote localhost:1234

and the second with an additional next command.

My setup

Platform: Linux-6.5.0-28-generic-x86_64-with-glibc2.35
OS: Ubuntu 22.04.4 LTS
OS ABI: #29~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Thu Apr  4 14:39:20 UTC 2
Architecture: x86_64
Endian: little
Charset: utf-8
Width: 101
Height: 57
Gdb:      12.1
Python:   3.10.12 (main, Nov 20 2023, 15:14:05) [GCC 11.4.0]
Pwndbg:   2024.02.14 build: 00adfbbb
Capstone: 5.0.1280
Unicorn:  2.0.1
This GDB was configured as follows:
   configure --host=x86_64-linux-gnu --target=x86_64-linux-gnu
	     --with-auto-load-dir=$debugdir:$datadir/auto-load
	     --with-auto-load-safe-path=$debugdir:$datadir/auto-load
	     --with-expat
	     --with-gdb-datadir=/usr/share/gdb (relocatable)
	     --with-jit-reader-dir=/usr/lib/gdb (relocatable)
	     --without-libunwind-ia64
	     --with-lzma
	     --with-babeltrace
	     --with-intel-pt
	     --with-mpfr
	     --with-xxhash
	     --with-python=/usr (relocatable)
	     --with-python-libdir=/usr/lib (relocatable)
	     --with-debuginfod
	     --without-guile
	     --enable-source-highlight
	     --with-separate-debug-dir=/usr/lib/debug (relocatable)
	     --with-system-gdbinit=/etc/gdb/gdbinit
	     --with-system-gdbinit-dir=/etc/gdb/gdbinit.d

("Relocatable" means the directory can be moved with the GDB installation
tree, and GDB will still find it.)

pwndbg commit: 00adfbb

[gsingh93]

cc: @OBarronCS since this is in the emulation code you'll be refactoring.