Initial attempt at floating point debugging

interface/src/main.cpp

@@ -31,6 +31,7 @@
 #include <plugins/DisplayPlugin.h>
 #include <plugins/CodecPlugin.h>
 #include <shared/GlobalAppProperties.h>
+#include <fenv.h>
 
 #include "AddressManager.h"
 #include "Application.h"
@@ -49,6 +50,16 @@ extern "C" {
 }
 #endif
 
+#ifdef Q_OS_UNIX
+#include <csignal>
+static int fpe_counter = 0;
+static void fpe_handler(int signum) {
+    // This currently exists just to have something to pass to the SIGFPE handler,
+    // and to serve as a point where to put a breakpoint.
+    ++fpe_counter;
+}
+#endif
+
 int main(int argc, const char* argv[]) {
 #ifdef Q_OS_MAC
     auto format = getDefaultOpenGLSurfaceFormat();
@@ -372,6 +383,11 @@ int main(int argc, const char* argv[]) {
         "Which graphics API to target. Supports gl45, gl41, and gles32. Final API may vary based on system support.",
         "string"
     );
+    QCommandLineOption floatExceptionsOption(
+        "floatExcept",
+        "Trigger an exception for the chosen floating point conditions, comma separated:  divbyzero, inexact, invalid, overflow, underflow, all. This is a debugging option.",
+        "string"
+    );
 
     parser.addOption(urlOption);
     parser.addOption(protocolVersionOption);
@@ -419,6 +435,8 @@ int main(int argc, const char* argv[]) {
     parser.addOption(xrNoHandTrackingOption);
     parser.addOption(xrNoPalmPoseOption);
     parser.addOption(graphicsAPIOption);
+    parser.addOption(floatExceptionsOption);
+
 
     QString applicationPath;
     // A temporary application instance is needed to get the location of the running executable
@@ -585,6 +603,34 @@ int main(int argc, const char* argv[]) {
         return 0;
     }
 
+    if (parser.isSet(floatExceptionsOption)) {
+        QStringList opts = parser.value(floatExceptionsOption).split(",");
+        int flags = 0;
+
+        for (const auto &opt : opts) {
+            if (opt == "divbyzero") {
+                flags |= FE_DIVBYZERO;
+            } else if (opt == "inexact") {
+                flags |= FE_INEXACT;
+            } else if (opt == "invalid") {
+                flags |= FE_INVALID;
+            } else if (opt == "overflow") {
+                flags |= FE_OVERFLOW;
+            } else if (opt == "underflow") {
+                flags |= FE_UNDERFLOW;
+            } else if (opt == "all") {
+                flags = FE_ALL_EXCEPT;
+            } else {
+                qCritical() << "Invalid value for --floatExcept option: " << opt;
+                return 2;
+            }
+        }
+
+        feenableexcept(flags);
+#ifdef Q_OS_UNIX
+        signal(SIGFPE, fpe_handler);
+#endif
+    }
 
     static const QString APPLICATION_CONFIG_FILENAME = "config.json";
     QDir applicationDir(applicationPath);

libraries/qml/src/qml/OffscreenSurface.cpp

@@ -25,6 +25,7 @@
 #include <shared/ReadWriteLockable.h>
 #include <NetworkingConstants.h>
 #include <MetaverseAPI.h>
+#include <fenv.h>
 
 #include "Logging.h"
 #include "impl/SharedObject.h"
@@ -457,7 +458,26 @@ void OffscreenSurface::finishQmlLoad(QQmlComponent* qmlComponent,
         // Call this callback after rootitem is set, otherwise VrMenu wont work
         callback(qmlContext, newItem);
     }
+
+    // There's a huge amount of divides by zero that happen with floating point exceptions
+    // enabled. It makes useful debugging impossible, so we're selectively disabling them
+    // here. Unfortunately fedisableexcept isn't standard and not available on Windows.
+    //
+    // On Windows, this might be unusable. Perhaps some sort of modification to QML
+    // might be possible.
+#ifndef Q_OS_WIN
+    fexcept_t fflags;
+
+    fegetexceptflag(&fflags, FE_ALL_EXCEPT);
+    fedisableexcept(FE_ALL_EXCEPT);
+#endif
+
     qmlComponent->completeCreate();
+
+#ifndef Q_OS_WIN
+    fesetexceptflag(&fflags, FE_ALL_EXCEPT);
+#endif
+
     qmlComponent->deleteLater();
 }