Re: [patch/v2] simplify debugging in-container tests (and regular tests)

[DJ Delorie <dj at redhat dot com>]

> * Use a boolean WAIT_FOR_DEBUGGER supporting 1 or 0 value (true and false respectively).

Done.  Note: the test is still run as --direct if WAIT_FOR_DEBUGGER=0
but only because the code is simpler that way ;-)

> * Have the child write a *.x file for gdb to just run. Simplifies things.

Done!

> Why is this volatile?

Comment added.

> Florian already mentioned a small usleep here. Just kinder on the host
> system.

Added.  Note, however, that the test now almost always breaks deep
inside usleep() instead of right in the support code.


>From 859b271b6f95762c25f018a7eac43180f7546ce9 Mon Sep 17 00:00:00 2001
From: DJ Delorie <dj@redhat.com>
Date: Wed, 2 Oct 2019 14:46:46 -0400
Subject: Add wait-for-debugger test harness hooks

If WAIT_FOR_DEBUGGER is set to a non-zero value in the environment,
any test that runs will print some useful gdb information and wait
for gdb to attach to it and clear the "wait_for_debugger" variable.

diff --git a/support/support_test_main.c b/support/support_test_main.c
index 05ad92e688..0be1bd3d78 100644
--- a/support/support_test_main.c
+++ b/support/support_test_main.c
@@ -19,6 +19,7 @@
 #include <support/test-driver.h>
 #include <support/check.h>
 #include <support/temp_file-internal.h>
+#include <support/support.h>
 
 #include <assert.h>
 #include <errno.h>
@@ -36,6 +37,8 @@
 #include <time.h>
 #include <unistd.h>
 
+#include <xstdio.h>
+
 static const struct option default_options[] =
 {
   TEST_DEFAULT_OPTIONS
@@ -176,10 +179,55 @@ signal_handler (int sig)
   exit (1);
 }
 
+/* This must be volatile as it will be modified by the debugger.  */
+static volatile int wait_for_debugger = 0;
+
 /* Run test_function or test_function_argv.  */
 static int
 run_test_function (int argc, char **argv, const struct test_config *config)
 {
+  const char *wfd = getenv("WAIT_FOR_DEBUGGER");
+  if (wfd != NULL)
+    wait_for_debugger = atoi (wfd);
+  if (wait_for_debugger)
+    {
+      pid_t mypid;
+      FILE *gdb_script;
+      char *gdb_script_name;
+      int inside_container = 0;
+
+      mypid = getpid();
+      if (mypid < 3)
+	{
+	  const char *outside_pid = getenv("PID_OUTSIDE_CONTAINER");
+	  if (outside_pid)
+	    {
+	      mypid = atoi (outside_pid);
+	      inside_container = 1;
+	    }
+	}
+
+      gdb_script_name = (char *) xmalloc (strlen (argv[0]) + strlen (".gdb") + 1);
+      sprintf (gdb_script_name, "%s.gdb", argv[0]);
+      gdb_script = xfopen (gdb_script_name, "w");
+
+      fprintf (stderr, "Waiting for debugger, test process is pid %d\n", mypid);
+      fprintf (stderr, "gdb -x %s\n", gdb_script_name);
+      if (inside_container)
+	fprintf (gdb_script, "set sysroot %s/testroot.root\n", support_objdir_root);
+      fprintf (gdb_script, "file\n");
+      fprintf (gdb_script, "file %s\n", argv[0]);
+      fprintf (gdb_script, "symbol-file %s\n", argv[0]);
+      fprintf (gdb_script, "exec-file %s\n", argv[0]);
+      fprintf (gdb_script, "attach %ld\n", (long int) mypid);
+      fprintf (gdb_script, "set wait_for_debugger = 0\n");
+      fclose (gdb_script);
+    }
+
+  /* Wait for the debugger to set wait_for_debugger to zero.  */
+  while (wait_for_debugger)
+    usleep (1000);
+
   if (config->test_function != NULL)
     return config->test_function ();
   else if (config->test_function_argv != NULL)
@@ -229,6 +277,11 @@ support_test_main (int argc, char **argv, const struct test_config *config)
   unsigned int timeoutfactor = 1;
   pid_t termpid;
 
+  /* If we're debugging the test, we need to disable timeouts and use
+     the initial pid (esp if we're running inside a container).  */
+  if (getenv("WAIT_FOR_DEBUGGER") != NULL)
+    direct = 1;
+
   if (!config->no_mallopt)
     {
       /* Make uses of freed and uninitialized memory known.  Do not
diff --git a/support/test-container.c b/support/test-container.c
index 9c42d3ae2f..5d08979df3 100644
--- a/support/test-container.c
+++ b/support/test-container.c
@@ -676,6 +676,9 @@ main (int argc, char **argv)
   char *so_base;
   int do_postclean = 0;
 
+  int pipes[2];
+  char pid_buf[20];
+
   uid_t original_uid;
   gid_t original_gid;
   /* If set, the test runs as root instead of the user running the testsuite.  */
@@ -999,6 +1002,11 @@ main (int argc, char **argv)
   if (chdir (new_cwd_path) < 0)
     FAIL_EXIT1 ("Can't cd to new %s - ", new_cwd_path);
 
+  /* This is to pass the "outside" PID to the child, which will be PID
+     1.  */
+  if (pipe2 (pipes, O_CLOEXEC) < 0)
+    FAIL_EXIT1 ("Can't create pid pipe");
+
   /* To complete the containerization, we need to fork () at least
      once.  We can't exec, nor can we somehow link the new child to
      our parent.  So we run the child and propogate it's exit status
@@ -1010,6 +1018,12 @@ main (int argc, char **argv)
     {
       /* Parent.  */
       int status;
+
+      /* Send the child's "outside" pid to it.  */
+      write (pipes[1], &child, sizeof(child));
+      close (pipes[0]);
+      close (pipes[1]);
+
       waitpid (child, &status, 0);
 
       if (WIFEXITED (status))
@@ -1028,6 +1042,14 @@ main (int argc, char **argv)
   /* The rest is the child process, which is now PID 1 and "in" the
      new root.  */
 
+  /* Get our "outside" pid from our parent.  We use this to help with
+     debugging from outside the container.  */
+  read (pipes[0], &child, sizeof(child));
+  close (pipes[0]);
+  close (pipes[1]);
+  sprintf (pid_buf, "%lu", (long unsigned)child);
+  setenv ("PID_OUTSIDE_CONTAINER", pid_buf, 0);
+
   maybe_xmkdir ("/tmp", 0755);
 
   /* Now that we're pid 1 (effectively "root") we can mount /proc  */