Handle 64bit breakpoints of WOW64 processes as SIGINT

When a WOW64 process triggers a breakpoint exception in 64bit code (which
happens when a 64bit gdb calls DebugBreakProcess for a 32bit target),
gdb ignores the breakpoint (because Wow64GetThreadContext can only report
the pc of 32bit code, and there is not int3 at this location).

But if these 64bit breakpoint exceptions are handled as SIGINT, gdb
doesn't check for int3, and always stops the target.

gdb/ChangeLog:

2020-09-23  Hannes Domani  <ssbssa@yahoo.de>

	* nat/windows-nat.c (handle_exception): Handle 64bit breakpoints
	in WOW64 processes as SIGINT.
	* nat/windows-nat.h: Make wow64_process a shared variable.
	* windows-nat.c: Remove static wow64_process variable.

gdbserver/ChangeLog:

2020-09-23  Hannes Domani  <ssbssa@yahoo.de>

	* win32-low.cc: Remove local wow64_process variable.
	* win32-low.h: Remove local wow64_process variable.

7 files changed, 29 insertions, 7 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 241f3e7..3b851db 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2020-09-23  Hannes Domani  <ssbssa@yahoo.de>
+
+	* nat/windows-nat.c (handle_exception): Handle 64bit breakpoints
+	in WOW64 processes as SIGINT.
+	* nat/windows-nat.h: Make wow64_process a shared variable.
+	* windows-nat.c: Remove static wow64_process variable.
+
 2020-09-23  Tom Tromey  <tom@tromey.com>
 
 	PR symtab/25470:
diff --git a/gdb/nat/windows-nat.c b/gdb/nat/windows-nat.c
index be6db97..2cbbc0f 100644
--- a/gdb/nat/windows-nat.c
+++ b/gdb/nat/windows-nat.c
@@ -41,6 +41,7 @@ std::vector<pending_stop> pending_stops;
 EXCEPTION_RECORD siginfo_er;
 
 #ifdef __x86_64__
+bool wow64_process = false;
 bool ignore_first_breakpoint = false;
 #endif
 
@@ -240,6 +241,20 @@ handle_exception (struct target_waitstatus *ourstatus, bool debug_exceptions)
 	  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
 	  ignore_first_breakpoint = false;
 	}
+      else if (wow64_process)
+	{
+	  /* This breakpoint exception is triggered for WOW64 processes when
+	     reaching an int3 instruction in 64bit code.
+	     gdb checks for int3 in case of SIGTRAP, this fails because
+	     Wow64GetThreadContext can only report the pc of 32bit code, and
+	     gdb lets the target process continue.
+	     So handle it as SIGINT instead, then the target is stopped
+	     unconditionally.  */
+	  DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_BREAKPOINT");
+	  rec->ExceptionCode = DBG_CONTROL_C;
+	  ourstatus->value.sig = GDB_SIGNAL_INT;
+	  break;
+	}
 #endif
       /* FALLTHROUGH */
     case STATUS_WX86_BREAKPOINT:
diff --git a/gdb/nat/windows-nat.h b/gdb/nat/windows-nat.h
index f742db2..9bfcb16 100644
--- a/gdb/nat/windows-nat.h
+++ b/gdb/nat/windows-nat.h
@@ -215,6 +215,8 @@ extern std::vector<pending_stop> pending_stops;
 extern EXCEPTION_RECORD siginfo_er;
 
 #ifdef __x86_64__
+/* The target is a WOW64 process */
+extern bool wow64_process;
 /* Ignore first breakpoint exception of WOW64 process */
 extern bool ignore_first_breakpoint;
 #endif
diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index ba88c33..7fff41d 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -235,7 +235,6 @@ static std::vector<windows_thread_info *> thread_list;
 static int saw_create;
 static int open_process_used = 0;
 #ifdef __x86_64__
-static bool wow64_process = false;
 static void *wow64_dbgbreak;
 #endif
 
diff --git a/gdbserver/ChangeLog b/gdbserver/ChangeLog
index d47fcfd..c97d4b1 100644
--- a/gdbserver/ChangeLog
+++ b/gdbserver/ChangeLog
@@ -1,3 +1,8 @@
+2020-09-23  Hannes Domani  <ssbssa@yahoo.de>
+
+	* win32-low.cc: Remove local wow64_process variable.
+	* win32-low.h: Remove local wow64_process variable.
+
 2020-09-18  Tom Tromey  <tromey@adacore.com>
 
 	* netbsd-low.h (class netbsd_process_target) <wait>: Update.
diff --git a/gdbserver/win32-low.cc b/gdbserver/win32-low.cc
index 9980986..e5f85a1 100644
--- a/gdbserver/win32-low.cc
+++ b/gdbserver/win32-low.cc
@@ -91,10 +91,6 @@ static int faked_breakpoint = 0;
 /* True if current_process_handle needs to be closed.  */
 static bool open_process_used = false;
 
-#ifdef __x86_64__
-bool wow64_process = false;
-#endif
-
 const struct target_desc *win32_tdesc;
 #ifdef __x86_64__
 const struct target_desc *wow64_win32_tdesc;
diff --git a/gdbserver/win32-low.h b/gdbserver/win32-low.h
index d4ad5d8..8c113f8 100644
--- a/gdbserver/win32-low.h
+++ b/gdbserver/win32-low.h
@@ -30,8 +30,6 @@ extern const struct target_desc *win32_tdesc;
 #ifdef __x86_64__
 extern const struct target_desc *wow64_win32_tdesc;
 
-extern bool wow64_process;
-
 typedef BOOL (WINAPI *winapi_Wow64GetThreadContext) (HANDLE, PWOW64_CONTEXT);
 extern winapi_Wow64GetThreadContext win32_Wow64GetThreadContext;
 #endif