[lldb] Fix loading DLL from some ramdisk on Windows

The WinAPI `GetFinalPathNameByHandle` is used to retrieve the DLL file
name from the HANDLE provided to `LOAD_DLL_DEBUG_EVENT` in the debug
loop. When this API fails, lldb will simply ignore that module.

Certain ramdisk (e.g. ImDisk) does not work with this API, which means
it is impossible to use lldb to debug a process which loads DLLs located
on this type of ramdisk. In order to make this work, we need to use a
fallback routine which involves creating a file mapping, using
`GetMappedFileName` to get a device path, then substitutes the device
path with its drive letter.

References:
* https://developercommunity.visualstudio.com/t/cannot-debug-program-when-compiled-to-ram-drive/43004#T-N109926
* https://github.com/jrfonseca/drmingw/issues/65
* https://docs.microsoft.com/en-us/windows/win32/memory/obtaining-a-file-name-from-a-file-handle

Reviewed By: labath

Differential Revision: https://reviews.llvm.org/D126657

lldb/source/Plugins/Process/Windows/Common/DebuggerThread.cpp

@@ -13,6 +13,7 @@
 #include "lldb/Core/ModuleSpec.h"
 #include "lldb/Host/ProcessLaunchInfo.h"
 #include "lldb/Host/ThreadLauncher.h"
+#include "lldb/Host/windows/AutoHandle.h"
 #include "lldb/Host/windows/HostProcessWindows.h"
 #include "lldb/Host/windows/HostThreadWindows.h"
 #include "lldb/Host/windows/ProcessLauncherWindows.h"
@@ -29,6 +30,8 @@
 #include "llvm/Support/Threading.h"
 #include "llvm/Support/raw_ostream.h"
 
+#include <psapi.h>
+
 #ifndef STATUS_WX86_BREAKPOINT
 #define STATUS_WX86_BREAKPOINT 0x4000001FL // For WOW64
 #endif
@@ -409,6 +412,61 @@ DebuggerThread::HandleExitProcessEvent(const EXIT_PROCESS_DEBUG_INFO &info,
   return DBG_CONTINUE;
 }
 
+static llvm::Optional<std::string> GetFileNameFromHandleFallback(HANDLE hFile) {
+  // Check that file is not empty as we cannot map a file with zero length.
+  DWORD dwFileSizeHi = 0;
+  DWORD dwFileSizeLo = ::GetFileSize(hFile, &dwFileSizeHi);
+  if (dwFileSizeLo == 0 && dwFileSizeHi == 0)
+    return llvm::None;
+
+  AutoHandle filemap(
+      ::CreateFileMappingW(hFile, nullptr, PAGE_READONLY, 0, 1, NULL), nullptr);
+  if (!filemap.IsValid())
+    return llvm::None;
+
+  auto view_deleter = [](void *pMem) { ::UnmapViewOfFile(pMem); };
+  std::unique_ptr<void, decltype(view_deleter)> pMem(
+      ::MapViewOfFile(filemap.get(), FILE_MAP_READ, 0, 0, 1), view_deleter);
+  if (!pMem)
+    return llvm::None;
+
+  std::array<wchar_t, MAX_PATH + 1> mapped_filename;
+  if (!::GetMappedFileNameW(::GetCurrentProcess(), pMem.get(),
+                            mapped_filename.data(), mapped_filename.size()))
+    return llvm::None;
+
+  // A series of null-terminated strings, plus an additional null character
+  std::array<wchar_t, 512> drive_strings;
+  drive_strings[0] = L'\0';
+  if (!::GetLogicalDriveStringsW(drive_strings.size(), drive_strings.data()))
+    return llvm::None;
+
+  std::array<wchar_t, 3> drive = {L"_:"};
+  for (const wchar_t *it = drive_strings.data(); *it != L'\0';
+       it += wcslen(it) + 1) {
+    // Copy the drive letter to the template string
+    drive[0] = it[0];
+    std::array<wchar_t, MAX_PATH> device_name;
+    if (::QueryDosDeviceW(drive.data(), device_name.data(),
+                          device_name.size())) {
+      size_t device_name_len = wcslen(device_name.data());
+      if (device_name_len < mapped_filename.size()) {
+        bool match = _wcsnicmp(mapped_filename.data(), device_name.data(),
+                               device_name_len) == 0;
+        if (match && mapped_filename[device_name_len] == L'\\') {
+          // Replace device path with its drive letter
+          std::wstring rebuilt_path(drive.data());
+          rebuilt_path.append(&mapped_filename[device_name_len]);
+          std::string path_utf8;
+          llvm::convertWideToUTF8(rebuilt_path, path_utf8);
+          return path_utf8;
+        }
+      }
+    }
+  }
+  return llvm::None;
+}
+
 DWORD
 DebuggerThread::HandleLoadDllEvent(const LOAD_DLL_DEBUG_INFO &info,
                                    DWORD thread_id) {
@@ -420,6 +478,17 @@ DebuggerThread::HandleLoadDllEvent(const LOAD_DLL_DEBUG_INFO &info,
     return DBG_CONTINUE;
   }
 
+  auto on_load_dll = [&](llvm::StringRef path) {
+    FileSpec file_spec(path);
+    ModuleSpec module_spec(file_spec);
+    lldb::addr_t load_addr = reinterpret_cast<lldb::addr_t>(info.lpBaseOfDll);
+
+    LLDB_LOG(log, "Inferior {0} - DLL '{1}' loaded at address {2:x}...",
+             m_process.GetProcessId(), path, info.lpBaseOfDll);
+
+    m_debug_delegate->OnLoadDll(module_spec, load_addr);
+  };
+
   std::vector<wchar_t> buffer(1);
   DWORD required_size =
       GetFinalPathNameByHandleW(info.hFile, &buffer[0], 0, VOLUME_NAME_DOS);
@@ -434,14 +503,10 @@ DebuggerThread::HandleLoadDllEvent(const LOAD_DLL_DEBUG_INFO &info,
     if (path_str.startswith("\\\\?\\"))
       path += 4;
 
-    FileSpec file_spec(path);
+    on_load_dll(path);
-    ModuleSpec module_spec(file_spec);
+  } else if (llvm::Optional<std::string> path =
-    lldb::addr_t load_addr = reinterpret_cast<lldb::addr_t>(info.lpBaseOfDll);
+                 GetFileNameFromHandleFallback(info.hFile)) {
-
+    on_load_dll(*path);
-    LLDB_LOG(log, "Inferior {0} - DLL '{1}' loaded at address {2:x}...",
-             m_process.GetProcessId(), path, info.lpBaseOfDll);
-
-    m_debug_delegate->OnLoadDll(module_spec, load_addr);
   } else {
     LLDB_LOG(
         log,