Utils: Don't raise SIGSTOP in the process stub

Previously, the starting inferior was sent a SIGSTOP to avoid
progress before the debugger could attach.

However, these signals are then also visible in the debugger and
need to be ignored as part of the startup handling in Creator.

The waiting effect can be achieved less intrusively by waiting
on a pipe read between fork() and exec().

Task-number: QTCREATORBUG-25073
Task-number: QTCREATORBUG-25082
Task-number: QTCREATORBUG-25227
Change-Id: Ie70b9eb5ea865f85411c26b0dbf377a019fec8d5
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

share/qtcreator/debugger/lldbbridge.py

@@ -904,14 +904,6 @@ class Dumper(DumperBase):
             except:  # Could have been deleted in the mean time.
                 pass
 
-        self.ignoreStops = 0
-        if platform.system() == 'Linux':
-            if self.startMode_ == DebuggerStartMode.AttachCore:
-                pass
-            else:
-                if self.useTerminal_:
-                    self.ignoreStops = 1
-
         if self.platform_:
             self.debugger.SetCurrentPlatform(self.platform_)
         # sysroot has to be set *after* the platform
@@ -1450,9 +1442,6 @@ class Dumper(DumperBase):
                 if self.isInterrupting_:
                     self.isInterrupting_ = False
                     self.reportState("inferiorstopok")
-                elif self.ignoreStops > 0:
-                    self.ignoreStops -= 1
-                    self.process.Continue()
                 else:
                     self.reportState("stopped")
             else:

src/libs/utils/consoleprocess.cpp

@@ -611,6 +611,18 @@ bool ConsoleProcess::start()
     return true;
 }
 
+void Utils::ConsoleProcess::kickoffProcess()
+{
+#ifdef Q_OS_WIN
+    // Not used.
+#else
+    if (d->m_stubSocket && d->m_stubSocket->isWritable()) {
+        d->m_stubSocket->write("c", 1);
+        d->m_stubSocket->flush();
+    }
+#endif
+}
+
 void ConsoleProcess::interruptProcess()
 {
 #ifdef Q_OS_WIN

src/libs/utils/consoleprocess.h

@@ -90,6 +90,7 @@ public:
     bool isRunning() const; // This reflects the state of the console+stub
     qint64 applicationPID() const;
 
+    void kickoffProcess();
     void interruptProcess();
     void killProcess();
     void killStub();

src/libs/utils/process_stub_unix.c

@@ -57,6 +57,7 @@ extern char **environ;
 static int qtcFd;
 static char *sleepMsg;
 static int chldPipe[2];
+static int blockingPipe[2];
 static int isDebug;
 static volatile int isDetached;
 static volatile int chldPid;
@@ -236,10 +237,21 @@ int main(int argc, char *argv[])
         perror("Cannot create status pipe");
         doExit(3);
     }
+
     /* The debugged program is not supposed to inherit these handles. But we cannot
      * close the writing end before calling exec(). Just handle both ends the same way ... */
     fcntl(chldPipe[0], F_SETFD, FD_CLOEXEC);
     fcntl(chldPipe[1], F_SETFD, FD_CLOEXEC);
+
+    if (isDebug) {
+        /* Create execution start notification pipe. The child waits on this until
+           the parent writes to it, triggered by an 'c' message from Creator */
+        if (pipe(blockingPipe)) {
+            perror("Cannot create blocking pipe");
+            doExit(3);
+        }
+    }
+
     switch ((chldPid = fork())) {
         case -1:
             perror("Cannot fork child process");
@@ -262,9 +274,15 @@ int main(int argc, char *argv[])
 #ifdef __linux__
             prctl(PR_SET_PTRACER, atoi(argv[ArgPid]));
 #endif
-            /* Stop the child to allow the debugger to attach */
+            /* Block to allow the debugger to attach */
-            if (isDebug)
+            if (isDebug) {
-                kill(chldPid, SIGSTOP);
+                char buf;
+                int res = read(blockingPipe[0], &buf, 1);
+                if (res < 0)
+                    perror("Could not read from blocking pipe");
+                close(blockingPipe[0]);
+                close(blockingPipe[1]);
+            }
 
             if (env)
                 environ = env;
@@ -296,6 +314,7 @@ int main(int argc, char *argv[])
                     break;
                 } else {
                     int i;
+                    char c = 'i';
                     for (i = 0; i < nbytes; ++i) {
                         switch (buffer[i]) {
                         case 'k':
@@ -305,13 +324,12 @@ int main(int argc, char *argv[])
                                 kill(chldPid, SIGKILL);
                             }
                             break;
-                        case 'i':
+                        case 'c': {
-                            if (chldPid > 0) {
+                            int res = write(blockingPipe[1], &c, 1);
-                                int res = kill(chldPid, SIGINT);
+                            if (res < 0)
-                                if (res)
+                                perror("Could not write to blocking pipe");
-                                    perror("Stub could not interrupt inferior");
-                            }
                             break;
+                        }
                         case 'd':
                             isDetached = 1;
                             break;

src/plugins/debugger/gdb/gdbengine.cpp

@@ -1147,26 +1147,6 @@ void GdbEngine::handleStopResponse(const GdbMi &data)
         return;
     }
 
-    // Ignore signals from the process stub.
-    const GdbMi frame = data["frame"];
-    if (terminal()
-            && data["reason"].data() == "signal-received"
-            && data["signal-name"].data() == "SIGSTOP")
-    {
-        const QString from = frame["from"].data();
-        const QString func = frame["func"].data();
-        if (from.endsWith("/ld-linux.so.2")
-                || from.endsWith("/ld-linux-x86-64.so.2")
-                || func == "clone"
-                || func == "kill")
-        {
-            showMessage("INTERNAL CONTINUE AFTER SIGSTOP FROM STUB", LogMisc);
-            notifyInferiorSpontaneousStop();
-            continueInferiorInternal();
-            return;
-        }
-    }
-
     if (!m_onStop.isEmpty()) {
         notifyInferiorStopOk();
         showMessage("HANDLING QUEUED COMMANDS AFTER TEMPORARY STOP", LogMisc);
@@ -1184,6 +1164,7 @@ void GdbEngine::handleStopResponse(const GdbMi &data)
     QString fullName;
     QString function;
     QString language;
+    const GdbMi frame = data["frame"];
     if (frame.isValid()) {
         const GdbMi lineNumberG = frame["line"];
         function = frame["function"].data(); // V4 protocol
@@ -4919,7 +4900,9 @@ void GdbEngine::handleStubAttached(const DebuggerResponse &response, qint64 main
             notifyEngineRunAndInferiorStopOk();
             continueInferiorInternal();
         } else {
-            showMessage("INFERIOR ATTACHED AND RUNNING");
+            showMessage("INFERIOR ATTACHED");
+            QTC_ASSERT(terminal(), return);
+            terminal()->kickoffProcess();
             //notifyEngineRunAndInferiorRunOk();
             // Wait for the upcoming *stopped and handle it there.
         }

src/plugins/debugger/terminal.cpp

@@ -183,6 +183,11 @@ TerminalRunner::TerminalRunner(RunControl *runControl, const Runnable &stubRunna
             this, [this] { reportDone(); });
 }
 
+void TerminalRunner::kickoffProcess()
+{
+    m_stubProc.kickoffProcess();
+}
+
 void TerminalRunner::interruptProcess()
 {
     m_stubProc.interruptProcess();

src/plugins/debugger/terminal.h

@@ -77,6 +77,7 @@ public:
     qint64 applicationPid() const { return m_applicationPid; }
     qint64 applicationMainThreadId() const { return m_applicationMainThreadId; }
 
+    void kickoffProcess();
     void interruptProcess();
     void setRunAsRoot(bool on);