Share handle_exception

Both gdb and gdbserver have a "handle_exception" function, the bulk of
which is shared between the two implementations.  This patch arranges
for the entire thing to be moved into nat/windows-nat.c, with the
differences handled by callbacks.  This patch introduces one more
callback to make this possible.

gdb/ChangeLog
2020-04-08  Tom Tromey  <tromey@adacore.com>

	* windows-nat.c (MS_VC_EXCEPTION): Move to nat/windows-nat.c.
	(handle_exception_result): Move to nat/windows-nat.h.
	(DEBUG_EXCEPTION_SIMPLE): Remove.
	(windows_nat::handle_ms_vc_exception): New function.
	(handle_exception): Move to nat/windows-nat.c.
	(get_windows_debug_event): Update.
	(STATUS_WX86_BREAKPOINT, STATUS_WX86_SINGLE_STEP): Move to
	nat/windows-nat.c.
	* nat/windows-nat.h (handle_ms_vc_exception): Declare.
	(handle_exception_result): Move from windows-nat.c.
	(handle_exception): Declare.
	* nat/windows-nat.c (MS_VC_EXCEPTION, handle_exception)
	(STATUS_WX86_SINGLE_STEP, STATUS_WX86_BREAKPOINT): Move from
	windows-nat.c.

gdbserver/ChangeLog
2020-04-08  Tom Tromey  <tromey@adacore.com>

	* win32-low.c (handle_exception): Remove.
	(windows_nat::handle_ms_vc_exception): New function.
	(get_child_debug_event): Add "continue_status" parameter.
	Update.
	(win32_wait): Update.

2 files changed, 195 insertions, 0 deletions

diff --git a/gdb/nat/windows-nat.c b/gdb/nat/windows-nat.c
index 80a1583..6bbf41c 100644
--- a/gdb/nat/windows-nat.c
+++ b/gdb/nat/windows-nat.c
@@ -18,6 +18,10 @@
 
 #include "gdbsupport/common-defs.h"
 #include "nat/windows-nat.h"
+#include "gdbsupport/common-debug.h"
+
+#define STATUS_WX86_BREAKPOINT 0x4000001F
+#define STATUS_WX86_SINGLE_STEP 0x4000001E
 
 namespace windows_nat
 {
@@ -137,4 +141,175 @@ get_image_name (HANDLE h, void *address, int unicode)
   return buf;
 }
 
+/* The exception thrown by a program to tell the debugger the name of
+   a thread.  The exception record contains an ID of a thread and a
+   name to give it.  This exception has no documented name, but MSDN
+   dubs it "MS_VC_EXCEPTION" in one code example.  */
+#define MS_VC_EXCEPTION 0x406d1388
+
+handle_exception_result
+handle_exception (struct target_waitstatus *ourstatus, bool debug_exceptions)
+{
+#define DEBUG_EXCEPTION_SIMPLE(x)       if (debug_exceptions) \
+  debug_printf ("gdb: Target exception %s at %s\n", x, \
+    host_address_to_string (\
+      current_event.u.Exception.ExceptionRecord.ExceptionAddress))
+
+  EXCEPTION_RECORD *rec = &current_event.u.Exception.ExceptionRecord;
+  DWORD code = rec->ExceptionCode;
+  handle_exception_result result = HANDLE_EXCEPTION_HANDLED;
+
+  memcpy (&siginfo_er, rec, sizeof siginfo_er);
+
+  ourstatus->kind = TARGET_WAITKIND_STOPPED;
+
+  /* Record the context of the current thread.  */
+  thread_rec (ptid_t (current_event.dwProcessId, current_event.dwThreadId, 0),
+	      DONT_SUSPEND);
+
+  switch (code)
+    {
+    case EXCEPTION_ACCESS_VIOLATION:
+      DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_ACCESS_VIOLATION");
+      ourstatus->value.sig = GDB_SIGNAL_SEGV;
+#ifdef __CYGWIN__
+      {
+	/* See if the access violation happened within the cygwin DLL
+	   itself.  Cygwin uses a kind of exception handling to deal
+	   with passed-in invalid addresses.  gdb should not treat
+	   these as real SEGVs since they will be silently handled by
+	   cygwin.  A real SEGV will (theoretically) be caught by
+	   cygwin later in the process and will be sent as a
+	   cygwin-specific-signal.  So, ignore SEGVs if they show up
+	   within the text segment of the DLL itself.  */
+	const char *fn;
+	CORE_ADDR addr = (CORE_ADDR) (uintptr_t) rec->ExceptionAddress;
+
+	if ((!cygwin_exceptions && (addr >= cygwin_load_start
+				    && addr < cygwin_load_end))
+	    || (find_pc_partial_function (addr, &fn, NULL, NULL)
+		&& startswith (fn, "KERNEL32!IsBad")))
+	  return HANDLE_EXCEPTION_UNHANDLED;
+      }
+#endif
+      break;
+    case STATUS_STACK_OVERFLOW:
+      DEBUG_EXCEPTION_SIMPLE ("STATUS_STACK_OVERFLOW");
+      ourstatus->value.sig = GDB_SIGNAL_SEGV;
+      break;
+    case STATUS_FLOAT_DENORMAL_OPERAND:
+      DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_DENORMAL_OPERAND");
+      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      break;
+    case EXCEPTION_ARRAY_BOUNDS_EXCEEDED:
+      DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_ARRAY_BOUNDS_EXCEEDED");
+      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      break;
+    case STATUS_FLOAT_INEXACT_RESULT:
+      DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_INEXACT_RESULT");
+      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      break;
+    case STATUS_FLOAT_INVALID_OPERATION:
+      DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_INVALID_OPERATION");
+      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      break;
+    case STATUS_FLOAT_OVERFLOW:
+      DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_OVERFLOW");
+      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      break;
+    case STATUS_FLOAT_STACK_CHECK:
+      DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_STACK_CHECK");
+      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      break;
+    case STATUS_FLOAT_UNDERFLOW:
+      DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_UNDERFLOW");
+      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      break;
+    case STATUS_FLOAT_DIVIDE_BY_ZERO:
+      DEBUG_EXCEPTION_SIMPLE ("STATUS_FLOAT_DIVIDE_BY_ZERO");
+      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      break;
+    case STATUS_INTEGER_DIVIDE_BY_ZERO:
+      DEBUG_EXCEPTION_SIMPLE ("STATUS_INTEGER_DIVIDE_BY_ZERO");
+      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      break;
+    case STATUS_INTEGER_OVERFLOW:
+      DEBUG_EXCEPTION_SIMPLE ("STATUS_INTEGER_OVERFLOW");
+      ourstatus->value.sig = GDB_SIGNAL_FPE;
+      break;
+    case EXCEPTION_BREAKPOINT:
+#ifdef __x86_64__
+      if (ignore_first_breakpoint)
+	{
+	  /* For WOW64 processes, there are always 2 breakpoint exceptions
+	     on startup, first a BREAKPOINT for the 64bit ntdll.dll,
+	     then a WX86_BREAKPOINT for the 32bit ntdll.dll.
+	     Here we only care about the WX86_BREAKPOINT's.  */
+	  ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
+	  ignore_first_breakpoint = false;
+	}
+#endif
+      /* FALLTHROUGH */
+    case STATUS_WX86_BREAKPOINT:
+      DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_BREAKPOINT");
+      ourstatus->value.sig = GDB_SIGNAL_TRAP;
+#ifdef _WIN32_WCE
+      /* Remove the initial breakpoint.  */
+      check_breakpoints ((CORE_ADDR) (long) current_event
+			 .u.Exception.ExceptionRecord.ExceptionAddress);
+#endif
+      break;
+    case DBG_CONTROL_C:
+      DEBUG_EXCEPTION_SIMPLE ("DBG_CONTROL_C");
+      ourstatus->value.sig = GDB_SIGNAL_INT;
+      break;
+    case DBG_CONTROL_BREAK:
+      DEBUG_EXCEPTION_SIMPLE ("DBG_CONTROL_BREAK");
+      ourstatus->value.sig = GDB_SIGNAL_INT;
+      break;
+    case EXCEPTION_SINGLE_STEP:
+    case STATUS_WX86_SINGLE_STEP:
+      DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_SINGLE_STEP");
+      ourstatus->value.sig = GDB_SIGNAL_TRAP;
+      break;
+    case EXCEPTION_ILLEGAL_INSTRUCTION:
+      DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_ILLEGAL_INSTRUCTION");
+      ourstatus->value.sig = GDB_SIGNAL_ILL;
+      break;
+    case EXCEPTION_PRIV_INSTRUCTION:
+      DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_PRIV_INSTRUCTION");
+      ourstatus->value.sig = GDB_SIGNAL_ILL;
+      break;
+    case EXCEPTION_NONCONTINUABLE_EXCEPTION:
+      DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_NONCONTINUABLE_EXCEPTION");
+      ourstatus->value.sig = GDB_SIGNAL_ILL;
+      break;
+    case MS_VC_EXCEPTION:
+      DEBUG_EXCEPTION_SIMPLE ("MS_VC_EXCEPTION");
+      if (handle_ms_vc_exception (rec))
+	{
+	  ourstatus->value.sig = GDB_SIGNAL_TRAP;
+	  result = HANDLE_EXCEPTION_IGNORED;
+	  break;
+	}
+	/* treat improperly formed exception as unknown */
+	/* FALLTHROUGH */
+    default:
+      /* Treat unhandled first chance exceptions specially.  */
+      if (current_event.u.Exception.dwFirstChance)
+	return HANDLE_EXCEPTION_UNHANDLED;
+      debug_printf ("gdb: unknown target exception 0x%08x at %s\n",
+	(unsigned) current_event.u.Exception.ExceptionRecord.ExceptionCode,
+	host_address_to_string (
+	  current_event.u.Exception.ExceptionRecord.ExceptionAddress));
+      ourstatus->value.sig = GDB_SIGNAL_UNKNOWN;
+      break;
+    }
+
+  last_sig = ourstatus->value.sig;
+  return result;
+
+#undef DEBUG_EXCEPTION_SIMPLE
+}
+
 }
diff --git a/gdb/nat/windows-nat.h b/gdb/nat/windows-nat.h
index 2b2fd11..a4e0b39 100644
--- a/gdb/nat/windows-nat.h
+++ b/gdb/nat/windows-nat.h
@@ -143,6 +143,16 @@ extern void handle_load_dll ();
 
 extern void handle_unload_dll ();
 
+/* Handle MS_VC_EXCEPTION when processing a stop.  MS_VC_EXCEPTION is
+   somewhat undocumented but is used to tell the debugger the name of
+   a thread.
+
+   Return true if the exception was handled; return false otherwise.
+
+   This function must be supplied by the embedding application.  */
+
+extern bool handle_ms_vc_exception (const EXCEPTION_RECORD *rec);
+
 
 /* Currently executing process */
 extern HANDLE current_process_handle;
@@ -205,6 +215,16 @@ extern EXCEPTION_RECORD siginfo_er;
    get_image_name.  */
 extern const char *get_image_name (HANDLE h, void *address, int unicode);
 
+typedef enum
+{
+  HANDLE_EXCEPTION_UNHANDLED = 0,
+  HANDLE_EXCEPTION_HANDLED,
+  HANDLE_EXCEPTION_IGNORED
+} handle_exception_result;
+
+extern handle_exception_result handle_exception
+  (struct target_waitstatus *ourstatus, bool debug_exceptions);
+
 }
 
 #endif