[lldb][Android] Fix adb shell cat

[splhack]

Summary

When LLDB failed to pull a module file due to the security constraint,
it uses "adb shell cat" as a fallback for getting the file.
However when "adb pull path" fails, "adb shell cat path" also fails
with the same security reason.

Introduce ANDROID_PLATFORM_RUN_AS to grant permission to read the file
with "adb shell run-as package cat path" command line.
https://android.googlesource.com/platform/system/core.git/+/refs/heads/master/run-as/run-as.cpp#39

[lanza]

LGTM

[bulbazord]

An environment variable isn't the worst thing in the world, but what would be better is an lldb setting so we can change it at runtime instead of needing to restart the debugging session. That may happen if you make a typo or make a mistake. Something like plugin.platform.android.platform-run-as.

[splhack]

@bulbazord thanks for the suggestion! property works well. D152933 supersedes this.

lldb/docs/use/remote.rst

 commands: get-file, put-file, mkdir, etc. The environment can be prepared
 further using the platform shell command.
 
 When using the "remote-android" platform, the client LLDB forwards two ports, one
 for connecting to the platform, and another for connecting to the gdbserver.
 The client ports are configurable through the environment variables
 ANDROID_PLATFORM_LOCAL_PORT and ANDROID_PLATFORM_LOCAL_GDB_PORT, respectively.
 
+The "remote-android" platform requires ANDROID_PLATFORM_RUN_AS when target
+application install path is not accessible with "adb pull". LLDB will use
+"adb shell run-as $ANDROID_PLATFORM_RUN_AS cat path" to get module file.
+
 Launching a locally built process on the remote machine
 -------------------------------------------------------
 
 Install and run in the platform working directory
 *************************************************
 
 To launch a locally built process on the remote system in the platform working
 directory:

lldb/source/Plugins/Platform/Android/PlatformAndroid.cpp

 //===-- PlatformAndroid.cpp -----------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
Status PlatformAndroid::GetFile(const FileSpec &source,
   if (strchr(source_file.c_str(), '\'') != nullptr)
     return Status("Doesn't support single-quotes in filenames");
 
   // mode == 0 can signify that adbd cannot access the file due security
   // constraints - try "cat ..." as a fallback.
   AdbClient adb(m_device_id);
 
   char cmd[PATH_MAX];
+  if (const char *run_as = std::getenv("ANDROID_PLATFORM_RUN_AS"))
+    snprintf(cmd, sizeof(cmd), "run-as '%s' cat '%s'", run_as,
+             source_file.c_str());
+  else
     snprintf(cmd, sizeof(cmd), "cat '%s'", source_file.c_str());
 
   return adb.ShellToFile(cmd, minutes(1), destination);
 }
 
 Status PlatformAndroid::PutFile(const FileSpec &source,
                                 const FileSpec &destination, uint32_t uid,
                                 uint32_t gid) {
   if (IsHost() || !m_remote_platform_sp)