Add support for DelayForDebugger option on linux

renderdoc/os/posix/android/android_process.cpp

@@ -107,7 +107,7 @@ bool StopChildAtMain(pid_t childPid)
   return false;
 }
 
-void ResumeProcess(pid_t childPid)
+void ResumeProcess(pid_t childPid, uint32_t delay)
 {
 }
 

renderdoc/os/posix/apple/apple_process.cpp

@@ -157,7 +157,7 @@ bool StopChildAtMain(pid_t childPid)
   return false;
 }
 
-void ResumeProcess(pid_t childPid)
+void ResumeProcess(pid_t childPid, uint32_t delay)
 {
 }
 

renderdoc/os/posix/ggp/ggp_process.cpp

@@ -145,7 +145,7 @@ bool StopChildAtMain(pid_t childPid)
   return false;
 }
 
-void ResumeProcess(pid_t childPid)
+void ResumeProcess(pid_t childPid, uint32_t delay)
 {
 }
 

renderdoc/os/posix/linux/linux_hook.cpp

@@ -85,7 +85,7 @@ int GetIdentPort(pid_t childPid);
 
 void StopAtMainInChild();
 bool StopChildAtMain(pid_t childPid);
-void ResumeProcess(pid_t childPid);
+void ResumeProcess(pid_t childPid, uint32_t delay = 0);
 
 __attribute__((visibility("default"))) pid_t fork()
 {

renderdoc/os/posix/linux/linux_process.cpp

@@ -410,10 +410,70 @@ void StopAtMainInChild()
   raise(SIGSTOP);
 }
 
-void ResumeProcess(pid_t childPid)
+void ResumeProcess(pid_t childPid, uint32_t delaySeconds)
 {
   if(childPid != 0)
   {
+    // if we have a delay, see if the process is paused. If so then detach it but keep it stopped
+    // and wait to see if someone attaches
+    if(delaySeconds > 0)
+    {
+      uint64_t ip = get_child_ip(childPid);
+
+      if(ip != 0)
+      {
+        // detach but stop, to allow a debugger to attach
+        ptrace(PTRACE_DETACH, childPid, NULL, SIGSTOP);
+
+        rdcstr filename = StringFormat::Fmt("/proc/%u/status", childPid);
+
+        uint64_t start_nano = get_nanotime();
+        uint64_t end_nano = 0;
+
+        const uint64_t timeoutNanoseconds = uint64_t(delaySeconds) * 1000 * 1000 * 1000;
+
+        bool connected = false;
+
+        // watch for a tracer to attach
+        do
+        {
+          usleep(10);
+
+          rdcstr status;
+          FileIO::ReadAll(filename, status);
+
+          int32_t offs = status.find("TracerPid:");
+
+          if(offs < 0)
+            break;
+
+          status.erase(0, offs + sizeof("TracerPid:"));
+          status.trim();
+
+          end_nano = get_nanotime();
+
+          if(status[0] != '0')
+          {
+            RDCLOG("Debugger PID %u attached after %f seconds", atoi(status.c_str()),
+                   double(end_nano - start_nano) / 1000000000.0);
+            connected = true;
+            break;
+          }
+        } while(end_nano - start_nano < timeoutNanoseconds);
+
+        if(!connected)
+        {
+          RDCLOG("Timed out waiting for debugger, resuming");
+          kill(childPid, SIGCONT);
+        }
+        return;
+      }
+      else
+      {
+        RDCERR("Can't delay for debugger without ptrace, check ptrace_scope value");
+      }
+    }
+
     // try to detach and resume the process, ignoring any errors if we weren't tracing
     ptrace(PTRACE_DETACH, childPid, NULL, NULL);
   }

renderdoc/os/posix/posix_process.cpp

@@ -48,7 +48,7 @@ int GetIdentPort(pid_t childPid);
 // us check the ident port and resume.
 void StopAtMainInChild();
 bool StopChildAtMain(pid_t childPid);
-void ResumeProcess(pid_t childPid);
+void ResumeProcess(pid_t childPid, uint32_t delay = 0);
 
 #if ENABLED(RDOC_APPLE)
 
@@ -853,7 +853,7 @@ rdcpair<ReplayStatus, uint32_t> Process::LaunchAndInjectIntoProcess(
     // exponential wait to get it as soon as possible
     ret = GetIdentPort(childPid);
 
-    ResumeProcess(ret);
+    ResumeProcess(childPid, opts.delayForDebugger);
 
     if(waitForExit)
     {