[debugserver/Apple Silicon] Handoff connections when attaching to translated processes

[davide]

Summary

When we detect a process that the native debugserver cannot handle, handoff the connection fd to the translated debugserver.

[jasonmolenda]

With this patch, debugging a translated app will only work when we invoke debugserver with --fd for its communication back to lldb. e.g. running 'debugserver localhost:2000 --attach=translated-app' will pass -fd=-1 as a command line argument to /Library/Apple/usr/libexec/oah/debugserver. Doing this properly would involve passing the same hostspec:portnum that debugserver received in this case -- but could we at least error out in DNBProcessAttach if communcation_fd==-1 so it's clear that this is not yet a supported workflow?

[davide]

yeah, I think it's reasonable.

[davide]

Added the check that Jason requested.

[davide]

Reviewed by Jason privately.

[davide]

https://github.com/llvm/llvm-project/commit/57605758b5de3726eec1d6e587de1003af1ab5b7

lldb/tools/debugserver/source/DNB.cpp

   if (err_str && err_len > 0)
     err_str[0] = '\0';
 
+  if (getenv("LLDB_DEBUGSERVER_PATH") == NULL) {
+    int mib[] = {CTL_KERN, KERN_PROC, KERN_PROC_PID,
+                 static_cast<int>(attach_pid)};
+    struct kinfo_proc processInfo;
+    size_t bufsize = sizeof(processInfo);
+    if (sysctl(mib, (unsigned)(sizeof(mib) / sizeof(int)), &processInfo,
+               &bufsize, NULL, 0) == 0 &&
+        bufsize > 0) {
+
+      if ((processInfo.kp_proc.p_flag & P_TRANSLATED) == P_TRANSLATED) {
+        const char *translated_debugserver =
+            "/Library/Apple/usr/libexec/oah/debugserver";
+        char fdstr[16];
+        char pidstr[16];
+        extern int communication_fd;
+
+        if (communication_fd == -1) {
+          fprintf(stderr, "Trying to attach to a translated process with the "
+                          "native debugserver, exiting...\n");
+          exit(1);
+        }
+
+        snprintf(fdstr, sizeof(fdstr), "--fd=%d", communication_fd);
+        snprintf(pidstr, sizeof(pidstr), "--attach=%d", attach_pid);
+        execl(translated_debugserver, "--native-regs", "--setsid", fdstr,
+              "--handoff-attach-from-native", pidstr, (char *)0);
+        DNBLogThreadedIf(LOG_PROCESS, "Failed to launch debugserver for "
+                         "translated process: ", errno, strerror(errno));
+        __builtin_trap();
+      }
+    }
+  }
+
   pid_t pid = INVALID_NUB_PROCESS;
   MachProcessSP processSP(new MachProcess);
   if (processSP.get()) {

lldb/tools/debugserver/source/debugserver.cpp

            // -F localhost:1234 -- /bin/ls"
     {NULL, 0, NULL, 0}};
 
+int communication_fd = -1;
+
 // main
 int main(int argc, char *argv[]) {
   // If debugserver is launched with DYLD_INSERT_LIBRARIES, unset it so we

   int ch;
   int long_option_index = 0;
   int debug = 0;
-  int communication_fd = -1;
   std::string compile_options;
   std::string waitfor_pid_name; // Wait for a process that starts with this name
   std::string attach_pid_name;