[lldb] Handle an empty SBMemoryRegionInfo from scripted process

A scripted process implementation might return an SBMemoryRegionInfo
object in its implementation of `get_memory_region_containing_address`
which will have an address 0 and size 0, without realizing the
problems this can cause.  One problem happens when an expression
is run, and lldb needs to find part of the target's virtual address
space to store the result (actually stored in lldb's host memory),
it uses IRMemoryMap::FindSpace() to do that.  If the process supports
GetMemoryRegionInfo, FindSpace will step through the allocated
memory ranges looking for an unused one.  But if every request is
a memory region with address 0 + size 0, this loop will never
terminate.  Detect this kind of response from a scripted process
plugin and return an error, so callers iterating over the address
space can exit.

Added a test where I copied dummy_scripted_process.py from the
TestScriptedProcess.py existing test, and added a bad
`get_memory_region_containing_address` implementation.

rdar://139678032

Author: jasonmolenda

lldb/source/Plugins/Process/scripted/ScriptedProcess.cpp

@@ -288,8 +288,15 @@ Status ScriptedProcess::DoGetMemoryRegionInfo(lldb::addr_t load_addr,
                                               MemoryRegionInfo &region) {
   Status error;
   if (auto region_or_err =
-          GetInterface().GetMemoryRegionContainingAddress(load_addr, error))
+          GetInterface().GetMemoryRegionContainingAddress(load_addr, error)) {
     region = *region_or_err;
+    if (region.GetRange().GetRangeBase() == 0 &&
+        (region.GetRange().GetByteSize() == 0 ||
+         region.GetRange().GetByteSize() == LLDB_INVALID_ADDRESS)) {
+      error = Status::FromErrorString(
+          "Invalid memory region from scripted process");
+    }
+  }
 
   return error;
 }

lldb/test/API/functionalities/scripted_process_empty_memory_region/Makefile

@@ -0,0 +1,3 @@
+C_SOURCES := main.c
+
+include Makefile.rules

lldb/test/API/functionalities/scripted_process_empty_memory_region/TestScriptedProcessEmptyMemoryRegion.py

@@ -0,0 +1,33 @@
+"""
+Test python scripted process which returns an empty SBMemoryRegionInfo
+"""
+
+import os, shutil
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+from lldbsuite.test import lldbtest
+
+
+class ScriptedProcessEmptyMemoryRegion(TestBase):
+    NO_DEBUG_INFO_TESTCASE = True
+
+    def test_scripted_process_empty_memory_region(self):
+        """Test that lldb handles an empty SBMemoryRegionInfo object from
+        a scripted process plugin."""
+        self.build()
+
+        target = self.dbg.CreateTarget(self.getBuildArtifact("a.out"))
+        self.assertTrue(target, VALID_TARGET)
+
+        scripted_process_example_relpath = "dummy_scripted_process.py"
+        self.runCmd(
+            "command script import "
+            + os.path.join(self.getSourceDir(), scripted_process_example_relpath)
+        )
+
+        self.expect("memory region 0", error=True, substrs=["Invalid memory region"])
+
+        self.expect("expr -- 5", substrs=["5"])

lldb/test/API/functionalities/scripted_process_empty_memory_region/dummy_scripted_process.py

@@ -0,0 +1,137 @@
+import os, struct, signal
+
+from typing import Any, Dict
+
+import lldb
+from lldb.plugins.scripted_process import ScriptedProcess
+from lldb.plugins.scripted_process import ScriptedThread
+
+
+class DummyStopHook:
+    def __init__(self, target, args):
+        self.target = target
+        self.args = args
+
+    def handle_stop(self, exe_ctx, stream):
+        print("My DummyStopHook triggered. Printing args: \n%s" % self.args)
+        sp = exe_ctx.process.GetScriptedImplementation()
+        sp.handled_stop = True
+
+
+class DummyScriptedProcess(ScriptedProcess):
+    memory = None
+
+    def __init__(self, exe_ctx: lldb.SBExecutionContext, args: lldb.SBStructuredData):
+        super().__init__(exe_ctx, args)
+        self.threads[0] = DummyScriptedThread(self, None)
+        self.memory = {}
+        addr = 0x500000000
+        debugger = self.target.GetDebugger()
+        index = debugger.GetIndexOfTarget(self.target)
+        self.memory[addr] = "Hello, target " + str(index)
+        self.handled_stop = False
+
+    def read_memory_at_address(
+        self, addr: int, size: int, error: lldb.SBError
+    ) -> lldb.SBData:
+        data = lldb.SBData().CreateDataFromCString(
+            self.target.GetByteOrder(), self.target.GetCodeByteSize(), self.memory[addr]
+        )
+
+        return data
+
+    def get_memory_region_containing_address(
+        self, addr: int
+    ) -> lldb.SBMemoryRegionInfo:
+        return lldb.SBMemoryRegionInfo()
+
+    def write_memory_at_address(self, addr, data, error):
+        self.memory[addr] = data.GetString(error, 0)
+        return len(self.memory[addr]) + 1
+
+    def get_loaded_images(self):
+        return self.loaded_images
+
+    def get_process_id(self) -> int:
+        return 42
+
+    def should_stop(self) -> bool:
+        return True
+
+    def is_alive(self) -> bool:
+        return True
+
+    def get_scripted_thread_plugin(self):
+        return DummyScriptedThread.__module__ + "." + DummyScriptedThread.__name__
+
+    def my_super_secret_method(self):
+        if hasattr(self, "my_super_secret_member"):
+            return self.my_super_secret_member
+        else:
+            return None
+
+
+class DummyScriptedThread(ScriptedThread):
+    def __init__(self, process, args):
+        super().__init__(process, args)
+        self.frames.append({"pc": 0x0100001B00})
+
+    def get_thread_id(self) -> int:
+        return 0x19
+
+    def get_name(self) -> str:
+        return DummyScriptedThread.__name__ + ".thread-1"
+
+    def get_state(self) -> int:
+        return lldb.eStateStopped
+
+    def get_stop_reason(self) -> Dict[str, Any]:
+        return {"type": lldb.eStopReasonTrace, "data": {}}
+
+    def get_register_context(self) -> str:
+        return struct.pack(
+            "21Q",
+            1,
+            2,
+            3,
+            4,
+            5,
+            6,
+            7,
+            8,
+            9,
+            10,
+            11,
+            12,
+            13,
+            14,
+            15,
+            16,
+            17,
+            18,
+            19,
+            20,
+            21,
+        )
+
+
+def __lldb_init_module(debugger, dict):
+    # This is used when loading the script in an interactive debug session to
+    # automatically, register the stop-hook and launch the scripted process.
+    if not "SKIP_SCRIPTED_PROCESS_LAUNCH" in os.environ:
+        debugger.HandleCommand(
+            "target stop-hook add -k first -v 1 -k second -v 2 -P %s.%s"
+            % (__name__, DummyStopHook.__name__)
+        )
+        debugger.HandleCommand(
+            "process launch -C %s.%s" % (__name__, DummyScriptedProcess.__name__)
+        )
+    else:
+        print(
+            "Name of the class that will manage the scripted process: '%s.%s'"
+            % (__name__, DummyScriptedProcess.__name__)
+        )
+        print(
+            "Name of the class that will manage the stop-hook: '%s.%s'"
+            % (__name__, DummyStopHook.__name__)
+        )

lldb/test/API/functionalities/scripted_process_empty_memory_region/main.c

@@ -0,0 +1 @@
+int main() {}