[patch] simplify debugging in-container tests (and regular tests)

[DJ Delorie <dj at redhat dot com>]

The attached patch helps you debug tests, especially in-container
tests.  Demo first...

dj@envy pts/27 ~/tools/upstream/glibc.debugtests.build
$ WAIT_FOR_DEBUGGER=1 make test t=nss/tst-nss-test3
/envy/dj/bin/make -r PARALLELMFLAGS="" -C ../glibc.debugtests objdir=`pwd` test
. . .
../scripts/evaluate-test.sh nss/tst-nss-test3 $? false false > /envy/dj/tools/upstream/glibc.debugtests.build/nss/tst-nss-test3.test-result
Waiting for debugger, test process is pid 9643
gdb -se /envy/dj/tools/upstream/glibc.debugtests.build/nss/tst-nss-test3 /envy/dj/tools/upstream/glibc.debugtests.build/nss/tst-nss-test3 9643
(gdb) set sysroot /envy/dj/tools/upstream/glibc.debugtests.build/testroot.root
(gdb) set wait_for_debugger = 0
(gdb) b do_test
(gdb) c

Then cut-n-paste those into another window...

dj@envy pts/30 ~/tools/upstream/glibc.debugtests.build
$ gdb -se /envy/dj/tools/upstream/glibc.debugtests.build/nss/tst-nss-test3 /envy/dj/tools/upstream/glibc.debugtests.build/nss/tst-nss-test3 9643
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Reading symbols from /envy/dj/tools/upstream/glibc.debugtests.build/nss/tst-nss-test3...
Attaching to program: /envy/dj/tools/upstream/glibc.debugtests.build/nss/tst-nss-test3, process 9643
Error while mapping shared library sections:
Could not open `target:/lib64/libc.so.6' as an executable file: Operation not permitted
Error while mapping shared library sections:
Could not open `target:/lib64/ld-linux-x86-64.so.2' as an executable file: Operation not permitted

warning: Unable to find dynamic linker breakpoint function.
GDB will be unable to debug shared library initializers
and track explicitly loaded dynamic code.

warning: Target and debugger are in different PID namespaces; thread lists and other data are likely unreliable.  Connect to gdbserver inside the container.
run_test_function (argc=argc@entry=1, argv=argv@entry=0x7fffe3a9d578, config=<optimized out>, 
    config=<optimized out>) at support_test_main.c:205
205         ;

[ gdb ] set sysroot /envy/dj/tools/upstream/glibc.debugtests.build/testroot.root
Reading symbols from /envy/dj/tools/upstream/glibc.debugtests.build/testroot.root/lib64/libc.so.6...
Reading symbols from /envy/dj/tools/upstream/glibc.debugtests.build/testroot.root/lib64/ld-linux-x86-64.so.2...

[ gdb ] set wait_for_debugger = 0

[ gdb ] b do_test
Breakpoint 1 at 0x402970: file tst-nss-test3.c, line 116.

[ gdb ] c
Continuing.

Breakpoint 1, do_test () at tst-nss-test3.c:116
116       setgrent ();

[ gdb ] n
119       for (g = getgrent () ;

[ gdb ] s
getgrent () at ../nss/getXXent.c:81
81        __libc_lock_lock (lock);

[ gdb ] 
__lll_cas_lock (futex=0x7fc5eaf6f300 <lock>) at ../sysdeps/unix/sysv/linux/x86/lowlevellock.h:47
47        asm volatile ("cmpxchgl %2, %1"

[ gdb ] where
#0  __lll_cas_lock (futex=0x7fc5eaf6f300 <lock>) at ../sysdeps/unix/sysv/linux/x86/lowlevellock.h:47
#1  getgrent () at ../nss/getXXent.c:81
#2  0x0000000000402982 in do_test () at tst-nss-test3.c:119
#3  0x0000000000403165 in support_test_main (argc=1, argv=0x7fffe3a9d578, config=config@entry=0x7fffe3a9d440)
    at support_test_main.c:378
#4  0x00000000004022e5 in main (argc=<optimized out>, argv=<optimized out>) at ../support/test-driver.c:168



>From 39ba1c48e97fb75133f92863561f7dfda23d8d1a 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 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..c94b0333b7 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>
@@ -176,10 +177,32 @@ signal_handler (int sig)
   exit (1);
 }
 
+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)
 {
+  if (getenv("WAIT_FOR_DEBUGGER") != NULL)
+    {
+      pid_t mypid;
+      mypid = getpid();
+      if (mypid < 3)
+	{
+	  const char *outside_pid = getenv("PID_OUTSIDE_CONTAINER");
+	  if (outside_pid)
+	    mypid = atoi (outside_pid);
+	}
+      wait_for_debugger = 1;
+      fprintf(stderr, "Waiting for debugger, test process is pid %d\n", mypid);
+      fprintf(stderr, "gdb -se %s %s %d\n", argv[0], argv[0], mypid);
+      fprintf(stderr, "(gdb) set sysroot %s/testroot.root\n", support_objdir_root);
+      fprintf(stderr, "(gdb) set wait_for_debugger = 0\n");
+      fprintf(stderr, "(gdb) b do_test\n");
+      fprintf(stderr, "(gdb) c\n");
+    }
+  while (wait_for_debugger)
+    ;
   if (config->test_function != NULL)
     return config->test_function ();
   else if (config->test_function_argv != NULL)
@@ -229,6 +252,11 @@ 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  */