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Date: Wed, 29 Apr 2020 10:54:25 +0000 (UTC)
From: Hannes Domani <ssbssa@yahoo.de>
To: Gdb-patches <gdb-patches@sourceware.org>
Message-ID: <471105047.4011567.1588157665165@mail.yahoo.com>
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 <7ec0c0b7-5425-d766-326b-9d5b13b755b4@simark.ca>
Subject: Re: [PATCH v2] Implement debugging of WOW64 processes in gdbserver
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 Am Dienstag, 28. April 2020, 17:53:15 MESZ hat Simon Marchi <simark@simark=
.ca> Folgendes geschrieben:

> On 2020-04-27 9:34 a.m., Hannes Domani via Gdb-patches wrote:
> > @@ -496,7 +601,7 @@ i386_win32_set_pc (struct regcache *regcache, CORE_=
ADDR pc)
> >
> >=C2=A0 struct win32_target_ops the_low_target =3D {
> >=C2=A0=C2=A0=C2=A0 i386_arch_setup,
> > -=C2=A0 sizeof (mappings) / sizeof (mappings[0]),
> > +=C2=A0 i386_win32_num_regs,
> >=C2=A0=C2=A0=C2=A0 i386_initial_stuff,
> >=C2=A0=C2=A0=C2=A0 i386_get_thread_context,
> >=C2=A0=C2=A0=C2=A0 i386_prepare_to_resume,
> > diff --git a/gdbserver/win32-low.cc b/gdbserver/win32-low.cc
> > index 5a6f0df39f..d3fc31914d 100644
> > --- a/gdbserver/win32-low.cc
> > +++ b/gdbserver/win32-low.cc
> > @@ -88,15 +88,32 @@ static int soft_interrupt_requested =3D 0;
> >=C2=A0=C2=A0=C2=A0 by suspending all the threads.=C2=A0 */
> >=C2=A0 static int faked_breakpoint =3D 0;
> >
> > +#ifdef __x86_64__
> > +bool wow64_process =3D false;
> > +#endif
> > +
> >=C2=A0 const struct target_desc *win32_tdesc;
> > +#ifdef __x86_64__
> > +const struct target_desc *wow64_win32_tdesc;
> > +#endif
> >
> > -#define NUM_REGS (the_low_target.num_regs)
> > +#define NUM_REGS (the_low_target.num_regs ())
> >
> >=C2=A0 typedef BOOL (WINAPI *winapi_DebugActiveProcessStop) (DWORD dwPro=
cessId);
> >=C2=A0 typedef BOOL (WINAPI *winapi_DebugSetProcessKillOnExit) (BOOL Kil=
lOnExit);
> >=C2=A0 typedef BOOL (WINAPI *winapi_DebugBreakProcess) (HANDLE);
> >=C2=A0 typedef BOOL (WINAPI *winapi_GenerateConsoleCtrlEvent) (DWORD, DW=
ORD);
> >
> > +#ifdef __x86_64__
> > +typedef DWORD (WINAPI *winapi_Wow64SuspendThread) (HANDLE);
> > +typedef BOOL (WINAPI *winapi_Wow64SetThreadContext) (HANDLE,
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 const WOW64_CONTEXT *);
> > +
> > +static winapi_Wow64SuspendThread win32_Wow64SuspendThread;
>
> win32_Wow64SuspendThread is never actually used, is this expected?

Well, in this case, kinda.
I only noticed afterwards that the same Wow64SuspendThread was unused in th=
e
gdb equivalent, because unexpectedly, SuspendThread does work (at least on
my PC).

But I will remove it from this patch, and will try to fix it for both
gdb & gdbserver with a later patch.


> > @@ -195,7 +231,14 @@ child_add_thread (DWORD pid, DWORD tid, HANDLE h, =
void *tlb)
> >=C2=A0=C2=A0=C2=A0 if ((th =3D thread_rec (ptid, DONT_INVALIDATE_CONTEXT=
)))
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return th;
> >
> > -=C2=A0 th =3D new windows_thread_info (tid, h, (CORE_ADDR) (uintptr_t)=
 tlb);
> > +=C2=A0 CORE_ADDR base =3D (CORE_ADDR) (uintptr_t) tlb;
> > +#ifdef __x86_64__
> > +=C2=A0 /* For WOW64 processes, this is actually the pointer to the 64b=
it TIB,
> > +=C2=A0=C2=A0=C2=A0 and the 32bit TIB is exactly 2 pages after it.=C2=
=A0 */
>
> Do you have a reference for this, ideally from MSDN?=C2=A0 If so, it woul=
d be nice to
> include the link in the comment.

Sadly no, I could find no official document for this.

There is an alternative way for to get the 32bit TIB, via the address at
offset 0 of the 64bit TIB:
https://docs.microsoft.com/en-us/windows/win32/debug/thread-environment-blo=
ck--debugging-notes-

But even here it is mentioned that this may change in later Windows version=
s.


> > +=C2=A0 if (wow64_process)
> > +=C2=A0=C2=A0=C2=A0 base +=3D 0x2000;
>
> Could you make it a PAGE_SIZE macro, and wirte `2 * PAGE_SIZE` here?=C2=
=A0 It would
> make it more obvious that it matches the comment above.

OK.


> > +#endif
> > +=C2=A0 th =3D new windows_thread_info (tid, h, base);
> >
> >=C2=A0=C2=A0=C2=A0 add_thread (ptid, th);
> >
> > @@ -345,8 +388,27 @@ do_initial_child_stuff (HANDLE proch, DWORD pid, i=
nt attached)
> >
> >=C2=A0=C2=A0=C2=A0 memset (&current_event, 0, sizeof (current_event));
> >
> > +#ifdef __x86_64__
> > +=C2=A0 BOOL wow64;
> > +=C2=A0 if (IsWow64Process (proch, &wow64))
> > +=C2=A0=C2=A0=C2=A0 wow64_process =3D wow64;
>
> If this function fails, it means we couldn't get the information we reque=
sted.=C2=A0 In
> this case, I think we should error out, because we can't continue reliabl=
y.=C2=A0 So,
> something like:
>
> BOOL wow64;
> if (!IsWow64Process (proch, &wow64_process))
>=C2=A0=C2=A0 {
>=C2=A0=C2=A0=C2=A0=C2=A0 // Call error() with a message formatted from Get=
LastError().
>=C2=A0=C2=A0 }

OK.


> > @@ -1096,13 +1197,53 @@ win32_add_all_dlls (void)
> >=C2=A0=C2=A0=C2=A0 if (!DllHandle)
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return;
> >
> > -=C2=A0 ok =3D (*win32_EnumProcessModules) (current_process_handle,
> > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 DllHandle,
> > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 cbNeeded,
> > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 &cbNeeded);
> > +#ifdef __x86_64__
> > +=C2=A0 if (wow64_process)
> > +=C2=A0=C2=A0=C2=A0 ok =3D (*win32_EnumProcessModulesEx) (current_proce=
ss_handle,
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 DllHandle,
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 cbNeeded,
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 &cbNeeded,
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 LIST_MODULES_32BIT);
> > +=C2=A0 else
> > +#endif
> > +=C2=A0=C2=A0=C2=A0 ok =3D (*win32_EnumProcessModules) (current_process=
_handle,
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 DllHandle,
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 cbNeeded,
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 &cbNeeded);
> >=C2=A0=C2=A0=C2=A0 if (!ok)
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return;
> >
> > +=C2=A0 char system_dir[MAX_PATH];
> > +=C2=A0 char syswow_dir[MAX_PATH];
> > +=C2=A0 size_t system_dir_len =3D 0;
> > +=C2=A0 bool convert_syswow_dir =3D false;
> > +#ifdef __x86_64__
> > +=C2=A0 if (wow64_process)
> > +#endif
> > +=C2=A0=C2=A0=C2=A0 {
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* This fails on 32bit Windows because =
it has no SysWOW64 directory,
> > +=C2=A0=C2=A0=C2=A0 and in this case a path conversion isn't necessary.=
=C2=A0 */
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 UINT len =3D GetSystemWow64DirectoryA (=
syswow_dir, sizeof (syswow_dir));
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (len > 0)
> > +=C2=A0=C2=A0=C2=A0 {
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* Check that we have passed a large en=
ough buffer.=C2=A0 */
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 gdb_assert (len < sizeof (syswow_dir));
> > +
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 len =3D GetSystemDirectoryA (system_dir=
, sizeof (system_dir));
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* Error check.=C2=A0 */
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 gdb_assert (len !=3D 0);
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* Check that we have passed a large en=
ough buffer.=C2=A0 */
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 gdb_assert (len < sizeof (system_dir));
> > +
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 strcat (system_dir, "\\");
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 strcat (syswow_dir, "\\");
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 system_dir_len =3D strlen (system_dir);
> > +
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 convert_syswow_dir =3D true;
> > +=C2=A0=C2=A0=C2=A0 }
> > +
> > +=C2=A0=C2=A0=C2=A0 }
>
> Since this is copied from gdb/windows-nat.c, it would be nice to factor i=
t
> out (as well as the small snippet below), so it can be shared.=C2=A0 Othe=
rwise,
> if we make a fix to one, we'll most likely forget to fix the other.
>
> The shared versions would go into gdb/nat/windows-nat.c.

There might be even more code that can be shared now, I planned to do this
with a later patch.


> > +
> >=C2=A0=C2=A0=C2=A0 for (i =3D 1; i < ((size_t) cbNeeded / sizeof (HMODUL=
E)); i++)
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 {
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 MODULEINFO mi;
> > @@ -1118,7 +1259,22 @@ win32_add_all_dlls (void)
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 dll_name,
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 MAX_PATH) =3D=3D 0)
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 continue;
> > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 win32_add_one_solib (dll_name, (CORE_AD=
DR) (uintptr_t) mi.lpBaseOfDll);
> > +
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 const char *name =3D dll_name;
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* Convert the DLL path of 32bit proces=
ses returned by
> > +=C2=A0=C2=A0=C2=A0 GetModuleFileNameEx from the 64bit system directory=
 to the
> > +=C2=A0=C2=A0=C2=A0 32bit syswow64 directory if necessary.=C2=A0 */
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 std::string syswow_dll_path;
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (convert_syswow_dir
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 && strncasecmp (dll_name, system_dir, s=
ystem_dir_len) =3D=3D 0
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 && strchr (dll_name + system_dir_len, '=
\\') =3D=3D nullptr)
> > +=C2=A0=C2=A0=C2=A0 {
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 syswow_dll_path =3D syswow_dir;
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 syswow_dll_path +=3D dll_name + system_=
dir_len;
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 name =3D syswow_dll_path.c_str();
> > +=C2=A0=C2=A0=C2=A0 }
> > +
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 win32_add_one_solib (name, (CORE_ADDR) =
(uintptr_t) mi.lpBaseOfDll);
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 }
> >=C2=A0 }
> >=C2=A0 #endif
> > @@ -1221,8 +1377,10 @@ maybe_adjust_pc ()
> >=C2=A0=C2=A0=C2=A0 th->stopped_at_software_breakpoint =3D false;
> >
> >=C2=A0=C2=A0=C2=A0 if (current_event.dwDebugEventCode =3D=3D EXCEPTION_D=
EBUG_EVENT
> > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 && (current_event.u.Exception.Exception=
Record.ExceptionCode
> > -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 =3D=3D EXCEPTION_BREAKPOINT)
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 && ((current_event.u.Exception.Exceptio=
nRecord.ExceptionCode
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 =3D=3D EXCEPTION_BREAKPOINT)
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 || (current_event.u.Exception.Exception=
Record.ExceptionCode
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 =3D=3D STATUS_W=
X86_BREAKPOINT))
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 && child_initialization_done)
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 {
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 th->stopped_at_software_break=
point =3D true;
> > @@ -1684,13 +1842,34 @@ win32_process_target::qxfer_siginfo (const char=
 *annex,
> >=C2=A0=C2=A0=C2=A0 if (readbuf =3D=3D nullptr)
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return -1;
> >
> > -=C2=A0 if (offset > sizeof (siginfo_er))
> > +=C2=A0 char *buf =3D (char *) &siginfo_er;
> > +=C2=A0 size_t bufsize =3D sizeof (siginfo_er);
> > +
> > +#ifdef __x86_64__
> > +=C2=A0 EXCEPTION_RECORD32 er32;
> > +=C2=A0 if (wow64_process)
> > +=C2=A0=C2=A0=C2=A0 {
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 buf =3D (char *) &er32;
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 bufsize =3D sizeof (er32);
> > +
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 er32.ExceptionCode =3D siginfo_er.Excep=
tionCode;
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 er32.ExceptionFlags =3D siginfo_er.Exce=
ptionFlags;
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 er32.ExceptionRecord =3D (uintptr_t) si=
ginfo_er.ExceptionRecord;
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 er32.ExceptionAddress =3D (uintptr_t) s=
iginfo_er.ExceptionAddress;
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 er32.NumberParameters =3D siginfo_er.Nu=
mberParameters;
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 int i;
> > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 for (i =3D 0; i < EXCEPTION_MAXIMUM_PAR=
AMETERS; i++)
> > +=C2=A0=C2=A0=C2=A0 er32.ExceptionInformation[i] =3D siginfo_er.Excepti=
onInformation[i];
> > +=C2=A0=C2=A0=C2=A0 }
> > +#endif
> > +
> > +=C2=A0 if (offset > bufsize)
> >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return -1;
> >
> > -=C2=A0 if (offset + len > sizeof (siginfo_er))
> > -=C2=A0=C2=A0=C2=A0 len =3D sizeof (siginfo_er) - offset;
> > +=C2=A0 if (offset + len > bufsize)
> > +=C2=A0=C2=A0=C2=A0 len =3D bufsize - offset;
> >
> > -=C2=A0 memcpy (readbuf, (char *) &siginfo_er + offset, len);
> > +=C2=A0 memcpy (readbuf, buf + offset, len);
> >
> >=C2=A0=C2=A0=C2=A0 return len;
> >=C2=A0 }
> > @@ -1760,4 +1939,11 @@ initialize_low (void)
> >=C2=A0 {
> >=C2=A0=C2=A0=C2=A0 set_target_ops (&the_win32_target);
> >=C2=A0=C2=A0=C2=A0 the_low_target.arch_setup ();
> > +
> > +#ifdef __x86_64__
> > +=C2=A0 HMODULE dll =3D GetModuleHandle (_T("KERNEL32.DLL"));
> > +=C2=A0 win32_Wow64SuspendThread =3D GETPROCADDRESS (dll, Wow64SuspendT=
hread);
> > +=C2=A0 win32_Wow64GetThreadContext =3D GETPROCADDRESS (dll, Wow64GetTh=
readContext);
> > +=C2=A0 win32_Wow64SetThreadContext =3D GETPROCADDRESS (dll, Wow64SetTh=
readContext);
>
> Why do we need to get these functions like this, instead of just calling =
them?

These functions are not available on WinXP, and the extra check for them
was actually the reason of this v2:

+=C2=A0 if (wow64_process
+=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 && (win32_Wow64SuspendThread =3D=3D nullptr
+=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 || win32_Wow64GetThreadContext =3D=3D nullp=
tr
+=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 || win32_Wow64SetThreadContext =3D=3D nullp=
tr))
+=C2=A0=C2=A0=C2=A0 error ("WOW64 debugging is not supported on this system=
.\n");


Hannes