reccmp: Don't use placeholder for address comparison (#751)

tools/isledecomp/isledecomp/compare/asm/parse.py

@@ -69,14 +69,16 @@ def float_replace(self, addr: int, data_size: int) -> Optional[str]:
 
         return None
 
-    def lookup(self, addr: int) -> Optional[str]:
+    def lookup(self, addr: int, use_cache: bool = True) -> Optional[str]:
         """Return a replacement name for this address if we find one."""
-        if (cached := self.replacements.get(addr, None)) is not None:
+        if use_cache and (cached := self.replacements.get(addr, None)) is not None:
             return cached
 
         if callable(self.name_lookup):
             if (name := self.name_lookup(addr)) is not None:
-                self.replacements[addr] = name
+                if use_cache:
+                    self.replacements[addr] = name
+
                 return name
 
         return None
@@ -110,6 +112,16 @@ def hex_replace_relocated(self, match: re.Match) -> str:
 
         return match.group(0)
 
+    def hex_replace_annotated(self, match: re.Match) -> str:
+        """For replacing immediate value operands. Here we replace the value
+        only if the name lookup returns something. Do not use a placeholder."""
+        value = int(match.group(1), 16)
+        placeholder = self.lookup(value, use_cache=False)
+        if placeholder is not None:
+            return match.group(0).replace(match.group(1), placeholder)
+
+        return match.group(0)
+
     def hex_replace_float(self, match: re.Match) -> str:
         """Special case for replacements on float instructions.
         If the pointer is a float constant, read it from the binary."""
@@ -178,7 +190,13 @@ def sanitize(self, inst: DisasmLiteInst) -> Tuple[str, str]:
             # vtable call, or this->member access.
             op_str = displace_replace_regex.sub(self.hex_replace_relocated, op_str)
 
-        op_str = immediate_replace_regex.sub(self.hex_replace_relocated, op_str)
+        # In the event of pointer comparison, only replace the immediate value
+        # if it is a known address.
+        if inst.mnemonic == "cmp":
+            op_str = immediate_replace_regex.sub(self.hex_replace_annotated, op_str)
+        else:
+            op_str = immediate_replace_regex.sub(self.hex_replace_relocated, op_str)
+
         return (inst.mnemonic, op_str)
 
     def parse_asm(self, data: bytes, start_addr: Optional[int] = 0) -> List[str]:

tools/isledecomp/tests/test_sanitize.py

@@ -221,3 +221,38 @@ def substitute_float(_: int, __: int) -> str:
     inst = DisasmLiteInst(0x1000, 6, "fld", "dword ptr [0x1234]")
     (_, op_str) = p.sanitize(inst)
     assert op_str == "dword ptr [g_myFloatVariable]"
+
+
+def test_pointer_compare():
+    """A loop on an array could get optimized into comparing on the address
+    that immediately follows the array. This may or may not be a valid address
+    and it may or may not be annotated. To avoid a situation where an
+    erroneous address value would get replaced with a placeholder and silently
+    pass the comparison check, we will only replace an immediate value on the
+    CMP instruction if it is a known address."""
+
+    # 0x1234 and 0x5555 are relocated and so are considered to be addresses.
+    def relocate_lookup(addr: int) -> bool:
+        return addr in (0x1234, 0x5555)
+
+    # Only 0x5555 is a "known" address
+    def name_lookup(addr: int) -> Optional[str]:
+        return "hello" if addr == 0x5555 else None
+
+    p = ParseAsm(relocate_lookup=relocate_lookup, name_lookup=name_lookup)
+
+    # Will always replace on MOV instruction
+    (_, op_str) = p.sanitize(mock_inst("mov", "eax, 0x1234"))
+    assert op_str == "eax, <OFFSET1>"
+    (_, op_str) = p.sanitize(mock_inst("mov", "eax, 0x5555"))
+    assert op_str == "eax, hello"
+
+    # n.b. We have already cached the replacement for 0x1234, but the
+    # special handling for CMP should skip the cache and not use it.
+
+    # Do not replace here
+    (_, op_str) = p.sanitize(mock_inst("cmp", "eax, 0x1234"))
+    assert op_str == "eax, 0x1234"
+    # Should replace here
+    (_, op_str) = p.sanitize(mock_inst("cmp", "eax, 0x5555"))
+    assert op_str == "eax, hello"