Fix exceptions during reverse execution in btrace (#1998)

pwndbg/chain.py

@@ -52,6 +52,9 @@ def get(
     Returns:
         A list representing pointers of each ```address``` and reference
     """
+    if address is None:
+        return None
+
     limit = int(limit)
 
     result = [address] if include_start else []
@@ -78,6 +81,10 @@ def get(
             result.append(address)
         except gdb.MemoryError:
             break
+        except gdb.error as e:
+            if str(e) == "value is not available":
+                break
+            raise
 
     return result
 
@@ -107,6 +114,9 @@ def format(value, limit=LIMIT, code=True, offset=0, hard_stop=None, hard_end=0,
         A string representing pointers of each address and reference
         Strings format: 0x0804a10 —▸ 0x08061000 ◂— 0x41414141
     """
+    if value is None:
+        return "<unavailable>"
+
     limit = int(limit)
 
     # Allow results from get function to be passed to format

pwndbg/color/context.py

@@ -88,6 +88,9 @@ def comment(x: object) -> str:
 
 
 def format_flags(value, flags, last=None):
+    if value is None:
+        return "<unavailable>"
+
     desc = flag_value("%#x" % value)
     if not flags:
         return desc

pwndbg/commands/telescope.py

@@ -108,7 +108,12 @@ def telescope(
     else:
         telescope.offset = 0
 
-    address = int(address if address else pwndbg.gdblib.regs.sp) & pwndbg.gdblib.arch.ptrmask
+    address = address if address else pwndbg.gdblib.regs.sp
+    if address is None:
+        print("Cannot display stack frame because stack pointer is unavailable")
+        return
+
+    address = int(address) & pwndbg.gdblib.arch.ptrmask
     input_address = address
     count = max(int(count), 1) & pwndbg.gdblib.arch.ptrmask
     delimiter = T.delimiter(offset_delimiter)

pwndbg/disasm/__init__.py

@@ -6,6 +6,7 @@ address +/- a few instructions.
 from __future__ import annotations
 
 import collections
+import re
 from typing import DefaultDict
 from typing import List
 from typing import Union
@@ -296,7 +297,15 @@ def near(address, instructions=1, emulate=False, show_prev_insns=True):
 
     # If we hit the current instruction, we can do emulation going forward from there.
     if address == pc and emulate and (not first_time_emulate or can_run_first_emulate()):
-        emu = pwndbg.emu.emulator.Emulator()
+        try:
+            emu = pwndbg.emu.emulator.Emulator()
+        except gdb.error as e:
+            message = str(e)
+            match = re.search(r"Memory at address (\w+) unavailable\.", message)
+            if match:
+                return []
+            else:
+                raise
         # skip current line
         emu.single_step()
 

pwndbg/disasm/x86.py

@@ -128,6 +128,8 @@ class DisassemblyAssistant(pwndbg.disasm.arch.DisassemblyAssistant):
             return False
 
         efl = pwndbg.gdblib.regs.eflags
+        if efl is None:
+            return False
 
         cf = efl & (1 << 0)
         pf = efl & (1 << 2)

pwndbg/gdblib/memory.py

@@ -5,6 +5,8 @@ Reading, writing, and describing memory.
 
 from __future__ import annotations
 
+import re
+
 import gdb
 
 import pwndbg.gdblib.arch
@@ -45,7 +47,13 @@ def read(addr: int, count: int, partial: bool = False) -> bytearray:
         if not hasattr(e, "message"):
             e.message = str(e)
 
-        stop_addr = int(e.message.split()[-1], 0)
+        stop_addr = addr
+        match = re.search(r"Memory at address (\w+) unavailable\.", e.message)
+        if match:
+            stop_addr = int(match.group(1), 0)
+        else:
+            stop_addr = int(e.message.split()[-1], 0)
+
         if stop_addr != addr:
             return read(addr, stop_addr - addr)