[PATCH v2] Fix WOW64 process system DLL paths

[Hannes Domani <ssbssa@yahoo.de>]

GetModuleFileNameEx returns for some DLLs of WOW64 processes
the path inside the 64bit system directory instead of the 32bit
syswow64 directory.

Problem happens e.g. with dbghelp.dll:

(gdb) start
Temporary breakpoint 1 at 0x415a00: file fiber.cpp, line 430.
Starting program: C:\src\tests\fiber.exe
warning: `C:\Windows\system32\dbghelp.dll': Shared library architecture i386:x86-64 is not compatible with target architecture i386.

Temporary breakpoint 1, main () at fiber.cpp:430
430     {
(gdb) info sharedlibrary
From        To          Syms Read   Shared Object Library
0x77070000  0x771d4d20  Yes (*)     C:\Windows\SysWOW64\ntdll.dll
0x74dc0000  0x74ebad9c  Yes (*)     C:\Windows\syswow64\kernel32.dll
0x75341000  0x75386a18  Yes (*)     C:\Windows\syswow64\KernelBase.dll
0x6f6a1000  0x6f7c48fc  Yes (*)     C:\Windows\system32\dbghelp.dll
0x74d01000  0x74dab2c4  Yes (*)     C:\Windows\syswow64\msvcrt.dll
(*): Shared library is missing debugging information.

This detects this situation and converts the DLL path to the
syswow64 equivalent.

gdb/ChangeLog:

2020-03-24  Hannes Domani  <ssbssa@yahoo.de>

	* windows-nat.c (windows_add_all_dlls): Fix system dll paths.
---
v2:
- added error check with gdb_assert's
- use std::string for newly assembled dll path
---
 gdb/windows-nat.c | 44 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 9c5ea5c046..8b7328946b 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -1993,16 +1993,39 @@ windows_add_all_dlls (void)
 	return;
     }
 
+#ifdef __x86_64__
+  char system_dir[__PMAX];
+  char syswow_dir[__PMAX];
+  size_t system_dir_len = 0;
+  if (wow64_process)
+    {
+      UINT len = GetSystemDirectoryA (system_dir, sizeof (system_dir));
+      /* Error check.  */
+      gdb_assert (len != 0);
+      /* Check that we have passed a large enough buffer.  */
+      gdb_assert (len < sizeof (system_dir));
+
+      len = GetSystemWow64DirectoryA (syswow_dir, sizeof (syswow_dir));
+      /* Error check.  */
+      gdb_assert (len != 0);
+      /* Check that we have passed a large enough buffer.  */
+      gdb_assert (len < sizeof (syswow_dir));
+
+      strcat (system_dir, "\\");
+      strcat (syswow_dir, "\\");
+      system_dir_len = strlen (system_dir);
+    }
+#endif
   for (i = 1; i < (int) (cb_needed / sizeof (HMODULE)); i++)
     {
       MODULEINFO mi;
 #ifdef __USEWIDE
       wchar_t dll_name[__PMAX];
-      char name[__PMAX];
+      char dll_name_mb[__PMAX];
 #else
       char dll_name[__PMAX];
-      char *name;
 #endif
+      const char *name;
       if (GetModuleInformation (current_process_handle, hmodules[i],
 				&mi, sizeof (mi)) == 0)
 	continue;
@@ -2010,10 +2033,25 @@ windows_add_all_dlls (void)
 			       dll_name, sizeof (dll_name)) == 0)
 	continue;
 #ifdef __USEWIDE
-      wcstombs (name, dll_name, __PMAX);
+      wcstombs (dll_name_mb, dll_name, __PMAX);
+      name = dll_name_mb;
 #else
       name = dll_name;
 #endif
+#ifdef __x86_64__
+      /* Convert the DLL path of WOW64 processes returned by
+	 GetModuleFileNameEx from the 64bit system directory to the
+	 32bit syswow64 directory if necessary.  */
+      std::string syswow_dll_path;
+      if (wow64_process
+	  && strncasecmp (name, system_dir, system_dir_len) == 0
+	  && strchr (name + system_dir_len, '\\') == nullptr)
+	{
+	  syswow_dll_path = syswow_dir;
+	  syswow_dll_path += name + system_dir_len;
+	  name = syswow_dll_path.c_str();
+	}
+#endif
 
       solib_end->next = windows_make_so (name, mi.lpBaseOfDll);
       solib_end = solib_end->next;
-- 
2.25.2