Fix Windows debugging regression

The updated pending stop series introduced a regression in Windows
debugging.  When stopped at a software breakpoint, we would adjust the
PC each time it was requested -- however, more than a single
adjustment is incorrect.  This patch introduces a new flag that is
used to ensure the adjustment only happens a single time.

No similar change is needed in gdbserver, because it adjusts the PC in
a different way.

I still can't run the gdb test suite on Windows, but I can run the
internal AdaCore test suite there; and this fixes the regressions
there.

gdb/ChangeLog
2020-04-24  Tom Tromey  <tromey@adacore.com>

	* nat/windows-nat.h (struct windows_thread_info)
	<pc_adjusted>: New member.
	* windows-nat.c (windows_fetch_one_register): Check
	pc_adjusted.
	(windows_nat_target::get_windows_debug_event)
	(windows_nat_target::wait): Set pc_adjusted.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index c2dc2b6ba807ae91e039f9aaf6ae7aa0e5924fc5..102edfcbc1f2e45435544c9898084a8598ddb79b 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,12 @@
+2020-04-24  Tom Tromey  <tromey@adacore.com>
+
+       * nat/windows-nat.h (struct windows_thread_info)
+       <pc_adjusted>: New member.
+       * windows-nat.c (windows_fetch_one_register): Check
+       pc_adjusted.
+       (windows_nat_target::get_windows_debug_event)
+       (windows_nat_target::wait): Set pc_adjusted.
+
 2020-04-24  Tom de Vries  <tdevries@suse.de>
 
        * contrib/cc-with-tweaks.sh: Remove <exec>.gdb-index file handling.

diff --git a/gdb/nat/windows-nat.h b/gdb/nat/windows-nat.h
index 8d0fa9bd2165b730d49c470d15dd2e0bfcef4553..80c652b22a7422941ddb118ce2359d2c0d4db1a6 100644 (file)
--- a/gdb/nat/windows-nat.h
+++ b/gdb/nat/windows-nat.h
@@ -93,6 +93,11 @@ struct windows_thread_info
      breakpoint.  This is used to offset the PC when needed.  */
   bool stopped_at_software_breakpoint = false;
 
+  /* True if we've adjusted the PC after hitting a software
+     breakpoint, false otherwise.  This lets us avoid multiple
+     adjustments if the registers are read multiple times.  */
+  bool pc_adjusted = false;
+
   /* The name of the thread, allocated by xmalloc.  */
   gdb::unique_xmalloc_ptr<char> name;
 };

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index b857f82eb897434cc6e1fc21d569dc22fd8015e5..f52af9a12747aba5b4abd990d4345139c57be9ee 100644 (file)
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -604,6 +604,7 @@ windows_fetch_one_register (struct regcache *regcache,
   else
     {
       if (th->stopped_at_software_breakpoint
+         && !th->pc_adjusted
          && r == gdbarch_pc_regnum (gdbarch))
        {
          int size = register_size (gdbarch, r);
@@ -622,6 +623,8 @@ windows_fetch_one_register (struct regcache *regcache,
              value -= gdbarch_decr_pc_after_break (gdbarch);
              memcpy (context_offset, &value, size);
            }
+         /* Make sure we only rewrite the PC a single time.  */
+         th->pc_adjusted = true;
        }
       regcache->raw_supply (r, context_offset);
     }
@@ -1757,6 +1760,7 @@ windows_nat_target::get_windows_debug_event (int pid,
          ptid_t ptid = ptid_t (current_event.dwProcessId, thread_id, 0);
          th = thread_rec (ptid, INVALIDATE_CONTEXT);
          th->stopped_at_software_breakpoint = true;
+         th->pc_adjusted = false;
        }
       pending_stops.push_back ({thread_id, *ourstatus, current_event});
       thread_id = 0;
@@ -1835,7 +1839,11 @@ windows_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
                      || (current_event.u.Exception.ExceptionRecord.ExceptionCode
                          == STATUS_WX86_BREAKPOINT))
                  && windows_initialization_done)
-               current_windows_thread->stopped_at_software_breakpoint = true;
+               {
+                 current_windows_thread->stopped_at_software_breakpoint
+                   = true;
+                 current_windows_thread->pc_adjusted = false;
+               }
            }
 
          return result;