Hooks for out-of-process (OOP) debugger.

src/trusted/service_runtime/nacl_oop_debugger_hooks.c

+/*
+ * Copyright (c) 2011 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "native_client/src/trusted/service_runtime/nacl_oop_debugger_hooks.h"
+#include "native_client/src/trusted/service_runtime/sel_ldr.h"
+
+#ifdef NACL_WINDOWS
+/*
+ * Note: this function does not do anything if program
+ * is not running under debugger.
+ * If program (sel_ldr) is running under debugger, calling this function
+ * gives debugger a chance to modify state of the debuggee before
+ * resuming debuggee execution.
+ */
+void SendMessageToDebuggerAndHalt(const char *fmt, ...)
+    ATTRIBUTE_FORMAT_PRINTF(1, 2);
+
+void NaClOopDebuggerAppCreateHook(struct NaClApp *nap) {
+  if (NULL == nap)
+    return;
+  SendMessageToDebuggerAndHalt(
+      "-event AppCreate -nap %p -mem_start %p -user_entry_pt %p "
+      "-initial_entry_pt %p",
+      nap,
+      (void *) nap->mem_start,
+      (void *) nap->user_entry_pt,
+      (void *) nap->initial_entry_pt);
+}
+
+void NaClOopDebuggerThreadCreateHook(struct NaClAppThread *natp) {
+  SendMessageToDebuggerAndHalt("-event ThreadCreate -natp %p", natp);
+}
+
+void NaClOopDebuggerThreadExitHook(struct NaClAppThread *natp, int exit_code) {
+  SendMessageToDebuggerAndHalt("-event ThreadExit -natp %p -exit_code %d",
+                               natp,
+                               exit_code);
+}
+
+void NaClOopDebuggerAppExitHook(int exit_code) {
+  SendMessageToDebuggerAndHalt("-event AppExit -exit_code %d", exit_code);
+}
+
+#else
+/* placeholders for OOP debugger hooks on other platforms */
+void NaClOopDebuggerAppCreateHook(struct NaClApp *nap) {
+  UNREFERENCED_PARAMETER(nap);
+}
+
+void NaClOopDebuggerThreadCreateHook(struct NaClAppThread *natp,
+                                     int exit_code) {
+  UNREFERENCED_PARAMETER(natp);
+  UNREFERENCED_PARAMETER(exit_code);
+}
+void NaClOopDebuggerThreadExitHook(struct NaClAppThread *natp,
+                                   int exit_code) {
+  UNREFERENCED_PARAMETER(natp);
+  UNREFERENCED_PARAMETER(exit_code);
+}
+
+void NaClOopDebuggerAppExitHook(int exit_code) {
+}
+#endif
+
+#ifdef NACL_WINDOWS
+void SendMessageToDebuggerAndHalt(const char *fmt, ...) {
+#define kVarMsgSize 2048
+  /*
+   * Determines whether the calling process is being debugged by a debugger.
+   * IsDebuggerPresent() is a member of Windows Debugging API:
+   * http://msdn.microsoft.com/en-us/library/ms680345%28v=VS.85%29.aspx
+   */
+  if (IsDebuggerPresent()) {
+    /*
+     * Prefix has GUID string specific to our OOP debugger, so that it
+     * can differentiate it from other uses of 'OutputDebugString'.
+     */
+    char prefix[] = "{7AA7C9CF-89EC-4ed3-8DAD-6DC84302AB11} -version 1 ";

[bsy, 2011/06/13 21:23:42]

shouldn't this be char const prefix[] = "..."?  should the prefix bytes be
writable?

[garianov1, 2011/06/13 21:41:06]

Done.

+    char msg[sizeof(prefix) + kVarMsgSize];

[bsy, 2011/06/13 21:23:42]

note that trusted stack size used to be 32KB in size and was only recently
increased to 64KB.  a 2KB plus buffer automatic variable may cause problems if
this function is invoked at a bad place -- though it appears that the API isn't
intended to be called from sites that are nested too deeply in the syscall
processing.  Perhaps a comment in the .h file?

[garianov1, 2011/06/13 21:41:06]

Changed kVarMsgSize to 512, it should be plenty stll. 

+    char *post_pref_msg = msg + sizeof(prefix) - 1;
+    signed int res = 0;
+    va_list marker;
+
+    strcpy(msg, prefix);
+    va_start(marker, fmt);
+    res = _vsnprintf_s(post_pref_msg, kVarMsgSize, _TRUNCATE, fmt, marker);

[bsy, 2011/06/13 21:23:42]

msg is sizeof(prefix) + kVarMsgSize in size, but post_pref_msg is at the null
byte in prefix, or prefix + sizeof(prefix)-1.  (a "string" initializer for an
array allocates space for the terminating ASCII NUL too, so sizeof(prefix) ==
strlen(prefix)+1.)  so the available space -- for the sizeOfBuffer argument of
_vsnprintf_s -- is really kVarMsgSize+1.  asking for fewer usually isn't bad --
the suffix to the GUID is at most 2047 characters before the terminating ASCII
NUL, instead of 2048, and the API doesn't advertise kVarMsgSize anyway -- but
this appears to be a minor error.

[garianov1, 2011/06/13 21:41:06]

Done.

+    if (-1 != res) {
+      /*
+       * Sends a string to the debugger by raising OUTPUT_DEBUG_STRING_EVENT.
+       * OutputDebugString() is a member of Windows Debugging API:
+       * http://msdn.microsoft.com/en-us/library/aa363362%28v=VS.85%29.aspx
+       *
+       * It's conceptually eqvivalent to:
+       * ::RaiseException(MY_OWN_EXCEPTION_CODE, 0, 1, &msg);
+       * The difference is, raising MY_OWN_EXCEPTION_CODE can cause program
+       * to crash (if there's no VEH handler and no debugger; or can cause
+       * debugger to stop program (if debugger does not know about
+       * MY_OWN_EXCEPTION_CODE).
+       *
+       * On the contrary, using OutputDebugString() is safe, cc from MSDN page:
+       * "If the application has no debugger and the system debugger is not
+       * active, OutputDebugString does nothing."
+       */
+      OutputDebugStringA(msg);
+    }

[bsy, 2011/06/13 21:23:42]

should this abort if the buffer couldn't hold the message?  log?

[garianov1, 2011/06/13 21:41:06]

Sending partial message is probably better than aborting.

+  }
+#undef kVarMsgSize
+}
+/* Example of captured sel_ldr -> debugger messages:
+
+11.62454796 [6060] {7AA7C9CF-89EC-4ed3-8DAD-6DC84302AB11} -version 1 \
+  -event AppCreate -nap 00000000001CD3F0 -mem_start 0000000C00000000 \
+  -user_entry_pt 0000000000020080 -initial_entry_pt 0000000008000080
+11.62480354 [6060] {7AA7C9CF-89EC-4ed3-8DAD-6DC84302AB11} -version 1 \
+  -event ThreadCreate -natp 0000000002304C50
+...
+23.96814728 [6060] {7AA7C9CF-89EC-4ed3-8DAD-6DC84302AB11} -version 1 \
+    -event ThreadExit -natp 0000000002304C50 -exit_code 1
+23.96838570 [6060] {7AA7C9CF-89EC-4ed3-8DAD-6DC84302AB11} -version 1 \
+    -event AppExit -exit_code 1
+*/
+#endif
+