LRN: Adding vectored exception handling for W32 (#1965)

Whenever an exception occurs, and the process is not being debugged, it will run a debugger specified by GNUNET_DEBUGGER environment variable, and wait for it to attach.
The net effect is the same as using JIT debugging (AeDebug), but without the stack being broken by SEH (because VEH has a priority over SEH), which allows for fuller backtraces for any exception, not just for GNUNET_abort() calls.

diff --git a/src/datastore/perf_plugin_datastore.c b/src/datastore/perf_plugin_datastore.c
index 8f552c4ebebf8102a223e442401bdfe3f50e6f1a..1498c7330136258f04aaa721046af56deab84f37 100644 (file)
--- a/src/datastore/perf_plugin_datastore.c
+++ b/src/datastore/perf_plugin_datastore.c
@@ -37,7 +37,7 @@
  * those take too long to run them in the usual "make check"
  * sequence.  Hence the value used for shipping is tiny.
  */
-#define MAX_SIZE 1024LL * 1024 * 16 * 1
+#define MAX_SIZE 1024LL * 1024 * 16 * 10
 
 #define ITERATIONS 2
 

diff --git a/src/util/winproc.c b/src/util/winproc.c
index b5245313aa70b2bd9d47f15f57d092e02ad0175a..7cd80a939bcaf5bfd7f23f1b0ce03e3bbed5cc97 100644 (file)
--- a/src/util/winproc.c
+++ b/src/util/winproc.c
@@ -32,6 +32,9 @@
 #ifdef MINGW
 
 static HINSTANCE hNTDLL, hIphlpapi, hAdvapi, hNetapi;
+#ifdef W32_VEH
+static void *GNWinVEH_handle = NULL;
+#endif
 
 TNtQuerySystemInformation GNNtQuerySystemInformation;
 TGetIfEntry GNGetIfEntry;
@@ -77,6 +80,60 @@ plibc_panic (int err, char *msg)
        "%s", msg);
 }
 
+#ifdef W32_VEH
+/**
+ * Handles exceptions (useful for debugging).
+ * Issues a DebugBreak() call if the process is being debugged (not really
+ * useful - if the process is being debugged, this handler won't be invoked
+ * anyway). If it is not, runs a debugger from GNUNET_DEBUGGER env var,
+ * substituting first %u in it for PID, and the second one for the event,
+ * that should be set once the debugger attaches itself (otherwise the
+ * only way out of WaitForSingleObject() is to time out after 1 minute).
+ */
+LONG __stdcall
+GNWinVEH (PEXCEPTION_POINTERS ExceptionInfo)
+{
+  char debugger[MAX_PATH + 1];
+  char *debugger_env = NULL;
+  if (IsDebuggerPresent ())
+  {
+    DebugBreak ();
+    return EXCEPTION_CONTINUE_EXECUTION;
+  }
+  debugger_env = getenv ("GNUNET_DEBUGGER");
+  if (debugger_env != NULL)
+  {
+    STARTUPINFO si;
+    PROCESS_INFORMATION pi;
+    HANDLE event;
+    SECURITY_ATTRIBUTES sa;
+    memset (&si, 0, sizeof (si));
+    si.cb = sizeof (si);
+    memset (&pi, 0, sizeof (pi));
+    memset (&sa, 0, sizeof (sa));
+    sa.nLength = sizeof (sa);
+    sa.bInheritHandle = TRUE;
+    event = CreateEvent (&sa, FALSE, FALSE, NULL);
+    snprintf (debugger, MAX_PATH + 1, debugger_env, GetCurrentProcessId (), (uintptr_t) event);
+    debugger[MAX_PATH] = '\0';
+    if (0 != CreateProcessA (NULL, debugger, NULL, NULL, TRUE, CREATE_NEW_CONSOLE, NULL, NULL, &si, &pi))
+    {
+      CloseHandle (pi.hProcess);
+      CloseHandle (pi.hThread);
+      WaitForSingleObject (event, 60000);
+      CloseHandle (event);
+      if (IsDebuggerPresent ())
+      {
+        return EXCEPTION_CONTINUE_EXECUTION;
+      }
+    }
+    else
+      CloseHandle (event);
+  }
+  return EXCEPTION_CONTINUE_SEARCH;
+}
+#endif
+
 /**
  * @brief Initialize PlibC and set up Windows environment
  * @param logging context, NULL means stderr
@@ -95,6 +152,18 @@ GNInitWinEnv ()
   if (hNTDLL)
     return ret;
 
+#ifdef W32_VEH
+  if (GNWinVEH_handle == NULL)
+  {
+    GNWinVEH_handle = AddVectoredExceptionHandler (1, &GNWinVEH);
+    if (GNWinVEH_handle == NULL)
+    {
+      /* This is bad, but what can we do? */
+      printf ("Failed to set up an exception handler!\n");
+    }
+  }
+#endif
+
   hNTDLL = LoadLibrary ("ntdll.dll");
 
   /* Function to get CPU usage under Win NT */
@@ -242,6 +311,14 @@ GNShutdownWinEnv ()
 {
   plibc_shutdown ();
 
+#ifdef W32_VEH
+  if (GNWinVEH_handle != NULL)
+  {
+    RemoveVectoredExceptionHandler (GNWinVEH_handle);
+    GNWinVEH_handle = NULL;
+  }
+#endif
+
   FreeLibrary (hNTDLL);
   FreeLibrary (hIphlpapi);
   FreeLibrary (hAdvapi);