diff mbox series

[02/34] Windows gdb: Eliminate global current_process.dr[8] global

Message ID 20240507234233.371123-3-pedro@palves.net
State New
Headers
Series Windows non-stop mode |

Commit Message

Pedro Alves May 7, 2024, 11:42 p.m. UTC 
  current_process.dr needs to be per-thread for non-stop.  Actually, it
doesn't even need to exist at all.  We have the x86_debug_reg_state
recording intent, and then the
cygwin_get_dr/cygwin_get_dr6/cygwin_get_dr7 functions are registered
as x86_dr_low_type vector functions, so they should return the current
value in the inferior's registers.  See this comment in x86-dregs.c:

~~~
  /* In non-stop/async, threads can be running while we change the
     global dr_mirror (and friends).  Say, we set a watchpoint, and
     let threads resume.  Now, say you delete the watchpoint, or
     add/remove watchpoints such that dr_mirror changes while threads
     are running.  On targets that support non-stop,
     inserting/deleting watchpoints updates the global dr_mirror only.
     It does not update the real thread's debug registers; that's only
     done prior to resume.  Instead, if threads are running when the
     mirror changes, a temporary and transparent stop on all threads
     is forced so they can get their copy of the debug registers
     updated on re-resume.  Now, say, a thread hit a watchpoint before
     having been updated with the new dr_mirror contents, and we
     haven't yet handled the corresponding SIGTRAP.  If we trusted
     dr_mirror below, we'd mistake the real trapped address (from the
     last time we had updated debug registers in the thread) with
     whatever was currently in dr_mirror.  So to fix this, dr_mirror
     always represents intention, what we _want_ threads to have in
     debug registers.  To get at the address and cause of the trap, we
     need to read the state the thread still has in its debug
     registers.

     In sum, always get the current debug register values the current
     thread has, instead of trusting the global mirror.  If the thread
     was running when we last changed watchpoints, the mirror no
     longer represents what was set in this thread's debug
     registers.  */
~~~

This patch makes the Windows native target follow that model as well.

I don't understand why would windows_nat_target::resume want to call
SetThreadContext itself.  That duplicates things as it is currently
worrying about setting the debug registers as well.  windows_continue
also does that, and windows_nat_target::resume always calls it.  So
this patch simplifies windows_nat_target::resume too.

Change-Id: I2fe460341b598ad293ea60d5f702b10cefc30711
---
 gdb/nat/windows-nat.h  |   1 +
 gdb/windows-nat.c      | 151 ++++++++++++++++++-----------------------
 gdbserver/win32-low.cc |   1 +
 3 files changed, 68 insertions(+), 85 deletions(-)

Comments

Tom Tromey May 8, 2024, 3:02 p.m. UTC | #1 
>>>>> "Pedro" == Pedro Alves <pedro@palves.net> writes:

Pedro> This patch makes the Windows native target follow that model as well.

This looks good to me, though I am not super confident in my ability to
reason about it in the abstract.

Pedro> I don't understand why would windows_nat_target::resume want to call
Pedro> SetThreadContext itself.  That duplicates things as it is currently
Pedro> worrying about setting the debug registers as well.  windows_continue
Pedro> also does that, and windows_nat_target::resume always calls it.  So
Pedro> this patch simplifies windows_nat_target::resume too.

FWIW when doing work on windows-nat, I found a number of little
oddities, but generally just erred on the side of preserving them, since
it wasn't always clear to me what the ramifications were.  Your series
is a welcome and long-overdue cleanup.

Pedro> -	  /* Copy dr values from that thread.
Pedro> -	     But only if there were not modified since last stop.
Pedro> -	     PR gdb/2388 */

This was moved to https://sourceware.org/bugzilla/show_bug.cgi?id=9493
in the bugzilla migration.  Anyway I'm wondering if you tried this
example.  It didn't seem to come with a test case.

Tom
diff mbox series

Patch

diff --git a/gdb/nat/windows-nat.h b/gdb/nat/windows-nat.h
index f2b5d777016..3783f39051d 100644
--- a/gdb/nat/windows-nat.h
+++ b/gdb/nat/windows-nat.h
@@ -144,6 +144,7 @@  struct windows_process_info
 {
   /* The process handle */
   HANDLE handle = 0;
+  DWORD process_id = 0;
   DWORD main_thread_id = 0;
   enum gdb_signal last_sig = GDB_SIGNAL_0;
 
diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 5578ae250a6..0102511dc8d 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -97,8 +97,6 @@  struct windows_per_inferior : public windows_process_info
   void handle_unload_dll () override;
   bool handle_access_violation (const EXCEPTION_RECORD *rec) override;
 
-  uintptr_t dr[8] {};
-
   int windows_initialization_done = 0;
 
   std::vector<std::unique_ptr<windows_thread_info>> thread_list;
@@ -730,36 +728,12 @@  windows_nat_target::fetch_registers (struct regcache *regcache, int r)
 	{
 	  th->wow64_context.ContextFlags = CONTEXT_DEBUGGER_DR;
 	  CHECK (Wow64GetThreadContext (th->h, &th->wow64_context));
-	  /* Copy dr values from that thread.
-	     But only if there were not modified since last stop.
-	     PR gdb/2388 */
-	  if (!th->debug_registers_changed)
-	    {
-	      windows_process.dr[0] = th->wow64_context.Dr0;
-	      windows_process.dr[1] = th->wow64_context.Dr1;
-	      windows_process.dr[2] = th->wow64_context.Dr2;
-	      windows_process.dr[3] = th->wow64_context.Dr3;
-	      windows_process.dr[6] = th->wow64_context.Dr6;
-	      windows_process.dr[7] = th->wow64_context.Dr7;
-	    }
 	}
       else
 #endif
 	{
 	  th->context.ContextFlags = CONTEXT_DEBUGGER_DR;
 	  CHECK (GetThreadContext (th->h, &th->context));
-	  /* Copy dr values from that thread.
-	     But only if there were not modified since last stop.
-	     PR gdb/2388 */
-	  if (!th->debug_registers_changed)
-	    {
-	      windows_process.dr[0] = th->context.Dr0;
-	      windows_process.dr[1] = th->context.Dr1;
-	      windows_process.dr[2] = th->context.Dr2;
-	      windows_process.dr[3] = th->context.Dr3;
-	      windows_process.dr[6] = th->context.Dr6;
-	      windows_process.dr[7] = th->context.Dr7;
-	    }
 	}
       th->reload_context = false;
     }
@@ -1283,18 +1257,21 @@  windows_nat_target::windows_continue (DWORD continue_status, int id,
   for (auto &th : windows_process.thread_list)
     if (id == -1 || id == (int) th->tid)
       {
+	struct x86_debug_reg_state *state
+	  = x86_debug_reg_state (windows_process.process_id);
+
 #ifdef __x86_64__
 	if (windows_process.wow64_process)
 	  {
 	    if (th->debug_registers_changed)
 	      {
 		th->wow64_context.ContextFlags |= CONTEXT_DEBUG_REGISTERS;
-		th->wow64_context.Dr0 = windows_process.dr[0];
-		th->wow64_context.Dr1 = windows_process.dr[1];
-		th->wow64_context.Dr2 = windows_process.dr[2];
-		th->wow64_context.Dr3 = windows_process.dr[3];
+		th->wow64_context.Dr0 = state->dr_mirror[0];
+		th->wow64_context.Dr1 = state->dr_mirror[1];
+		th->wow64_context.Dr2 = state->dr_mirror[2];
+		th->wow64_context.Dr3 = state->dr_mirror[3];
 		th->wow64_context.Dr6 = DR6_CLEAR_VALUE;
-		th->wow64_context.Dr7 = windows_process.dr[7];
+		th->wow64_context.Dr7 = state->dr_control_mirror;
 		th->debug_registers_changed = false;
 	      }
 	    if (th->wow64_context.ContextFlags)
@@ -1319,12 +1296,12 @@  windows_nat_target::windows_continue (DWORD continue_status, int id,
 	    if (th->debug_registers_changed)
 	      {
 		th->context.ContextFlags |= CONTEXT_DEBUG_REGISTERS;
-		th->context.Dr0 = windows_process.dr[0];
-		th->context.Dr1 = windows_process.dr[1];
-		th->context.Dr2 = windows_process.dr[2];
-		th->context.Dr3 = windows_process.dr[3];
+		th->context.Dr0 = state->dr_mirror[0];
+		th->context.Dr1 = state->dr_mirror[1];
+		th->context.Dr2 = state->dr_mirror[2];
+		th->context.Dr3 = state->dr_mirror[3];
 		th->context.Dr6 = DR6_CLEAR_VALUE;
-		th->context.Dr7 = windows_process.dr[7];
+		th->context.Dr7 = state->dr_control_mirror;
 		th->debug_registers_changed = false;
 	      }
 	    if (th->context.ContextFlags)
@@ -1463,22 +1440,6 @@  windows_nat_target::resume (ptid_t ptid, int step, enum gdb_signal sig)
 	      fetch_registers (regcache, gdbarch_ps_regnum (gdbarch));
 	      th->wow64_context.EFlags |= FLAG_TRACE_BIT;
 	    }
-
-	  if (th->wow64_context.ContextFlags)
-	    {
-	      if (th->debug_registers_changed)
-		{
-		  th->wow64_context.Dr0 = windows_process.dr[0];
-		  th->wow64_context.Dr1 = windows_process.dr[1];
-		  th->wow64_context.Dr2 = windows_process.dr[2];
-		  th->wow64_context.Dr3 = windows_process.dr[3];
-		  th->wow64_context.Dr6 = DR6_CLEAR_VALUE;
-		  th->wow64_context.Dr7 = windows_process.dr[7];
-		  th->debug_registers_changed = false;
-		}
-	      CHECK (Wow64SetThreadContext (th->h, &th->wow64_context));
-	      th->wow64_context.ContextFlags = 0;
-	    }
 	}
       else
 #endif
@@ -1491,22 +1452,6 @@  windows_nat_target::resume (ptid_t ptid, int step, enum gdb_signal sig)
 	      fetch_registers (regcache, gdbarch_ps_regnum (gdbarch));
 	      th->context.EFlags |= FLAG_TRACE_BIT;
 	    }
-
-	  if (th->context.ContextFlags)
-	    {
-	      if (th->debug_registers_changed)
-		{
-		  th->context.Dr0 = windows_process.dr[0];
-		  th->context.Dr1 = windows_process.dr[1];
-		  th->context.Dr2 = windows_process.dr[2];
-		  th->context.Dr3 = windows_process.dr[3];
-		  th->context.Dr6 = DR6_CLEAR_VALUE;
-		  th->context.Dr7 = windows_process.dr[7];
-		  th->debug_registers_changed = false;
-		}
-	      CHECK (SetThreadContext (th->h, &th->context));
-	      th->context.ContextFlags = 0;
-	    }
 	}
     }
 
@@ -1887,19 +1832,15 @@  windows_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
 void
 windows_nat_target::do_initial_windows_stuff (DWORD pid, bool attaching)
 {
-  int i;
   struct inferior *inf;
 
   windows_process.last_sig = GDB_SIGNAL_0;
   windows_process.open_process_used = 0;
-  for (i = 0;
-       i < sizeof (windows_process.dr) / sizeof (windows_process.dr[0]);
-       i++)
-    windows_process.dr[i] = 0;
 #ifdef __CYGWIN__
   windows_process.cygwin_load_start = 0;
   windows_process.cygwin_load_end = 0;
 #endif
+  windows_process.process_id = pid;
   memset (&windows_process.current_event, 0,
 	  sizeof (windows_process.current_event));
   inf = current_inferior ();
@@ -3321,7 +3262,6 @@  cygwin_set_dr (int i, CORE_ADDR addr)
 {
   if (i < 0 || i > 3)
     internal_error (_("Invalid register %d in cygwin_set_dr.\n"), i);
-  windows_process.dr[i] = addr;
 
   for (auto &th : windows_process.thread_list)
     th->debug_registers_changed = true;
@@ -3333,8 +3273,6 @@  cygwin_set_dr (int i, CORE_ADDR addr)
 static void
 cygwin_set_dr7 (unsigned long val)
 {
-  windows_process.dr[7] = (CORE_ADDR) val;
-
   for (auto &th : windows_process.thread_list)
     th->debug_registers_changed = true;
 }
@@ -3344,26 +3282,69 @@  cygwin_set_dr7 (unsigned long val)
 static CORE_ADDR
 cygwin_get_dr (int i)
 {
-  return windows_process.dr[i];
+  windows_thread_info *th
+    = windows_process.thread_rec (inferior_ptid, DONT_INVALIDATE_CONTEXT);
+
+#ifdef __x86_64__
+  if (windows_process.wow64_process)
+    {
+      gdb_assert (th->wow64_context.ContextFlags != 0);
+      switch (i)
+	{
+	case 0:
+	  return th->wow64_context.Dr0;
+	case 1:
+	  return th->wow64_context.Dr1;
+	case 2:
+	  return th->wow64_context.Dr2;
+	case 3:
+	  return th->wow64_context.Dr3;
+	case 6:
+	  return th->wow64_context.Dr6;
+	case 7:
+	  return th->wow64_context.Dr7;
+	};
+    }
+  else
+#endif
+    {
+      gdb_assert (th->context.ContextFlags != 0);
+      switch (i)
+	{
+	case 0:
+	  return th->context.Dr0;
+	case 1:
+	  return th->context.Dr1;
+	case 2:
+	  return th->context.Dr2;
+	case 3:
+	  return th->context.Dr3;
+	case 6:
+	  return th->context.Dr6;
+	case 7:
+	  return th->context.Dr7;
+	};
+    }
+
+  gdb_assert_not_reached ("invalid x86 dr register number: %d", i);
 }
 
-/* Get the value of the DR6 debug status register from the inferior.
-   Here we just return the value stored in dr[6]
-   by the last call to thread_rec for current_event.dwThreadId id.  */
+/* Get the value of the DR6 debug status register from the
+   inferior.  */
+
 static unsigned long
 cygwin_get_dr6 (void)
 {
-  return (unsigned long) windows_process.dr[6];
+  return cygwin_get_dr (6);
 }
 
-/* Get the value of the DR7 debug status register from the inferior.
-   Here we just return the value stored in dr[7] by the last call to
-   thread_rec for current_event.dwThreadId id.  */
+/* Get the value of the DR7 debug status register from the
+   inferior.  */
 
 static unsigned long
 cygwin_get_dr7 (void)
 {
-  return (unsigned long) windows_process.dr[7];
+  return cygwin_get_dr (7);
 }
 
 /* Determine if the thread referenced by "ptid" is alive
diff --git a/gdbserver/win32-low.cc b/gdbserver/win32-low.cc
index f672e542d1b..cc314df8dbd 100644
--- a/gdbserver/win32-low.cc
+++ b/gdbserver/win32-low.cc
@@ -309,6 +309,7 @@  do_initial_child_stuff (HANDLE proch, DWORD pid, int attached)
 
   windows_process.last_sig = GDB_SIGNAL_0;
   windows_process.handle = proch;
+  windows_process.process_id = pid;
   windows_process.main_thread_id = 0;
 
   windows_process.soft_interrupt_requested = 0;