[PATCH] Implement basic threading support in the NetBSD target

[Kamil Rytarowski <n54@gmx.com>]

Use sysctl(3) as the portable interface to prompt NetBSD threads on
all supported NetBSD versions. In future newer versions could switch
to PT_LWPSTATUS ptrace(2) API that will be supported on NetBSD 10.0
and newer.

Implement as part of nbsd_nat_target:
 - thread_name()         - read descriptive thread name
 - thread_alive()        - check whether a thread is alive
 - post_attach()         - updates the list of threads after attach
 - update_thread_list()  - updates the list of threads
 - pid_to_str()          - translates ptid to a descriptive string

There are two local static functions:
 - nbsd_thread_lister()  - generic LWP lister for a specified pid
 - nbsd_add_threads()    - utility to update the list of threads

Now, GDB on NetBSD can attach to a multithreaded process, spawn
a multithreaded process, list threads, print their LWP+PID numbers
and descriptive thread names.

gdb/ChangeLog:

       * nbsd-nat.h (struct thread_info): Add forward declaration.
       (nbsd_nat_target::thread_alive): Add.
       (nbsd_nat_target::thread_name): Likewise.
       (nbsd_nat_target::update_thread_list): Likewise.
       (update_thread_list::post_attach): Likewise.
       (post_attach::pid_to_str): Likewise.
       * nbsd-nat.c: Include "gdbthread.h" and "inferior.h".
       (nbsd_thread_lister): Add.
       (nbsd_nat_target::thread_alive): Likewise.
       (nbsd_nat_target::thread_name): Likewise.
       (nbsd_add_threads): Likewise.
       (update_thread_list::post_attach): Likewise.
       (nbsd_nat_target::update_thread_list): Likewise.
       (post_attach::pid_to_str): Likewise.
---
 gdb/ChangeLog  |  17 ++++++
 gdb/nbsd-nat.c | 161 +++++++++++++++++++++++++++++++++++++++++++++++++
 gdb/nbsd-nat.h |   8 +++
 3 files changed, 186 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1ee58a541cb..f31a7cf236c 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,20 @@
+2020-03-25  Kamil Rytarowski  <n54@gmx.com>
+
+	* nbsd-nat.h (struct thread_info): Add forward declaration.
+	(nbsd_nat_target::thread_alive): Add.
+	(nbsd_nat_target::thread_name): Likewise.
+	(nbsd_nat_target::update_thread_list): Likewise.
+	(update_thread_list::post_attach): Likewise.
+	(post_attach::pid_to_str): Likewise.
+	* nbsd-nat.c: Include "gdbthread.h" and "inferior.h".
+	(nbsd_thread_lister): Add.
+	(nbsd_nat_target::thread_alive): Likewise.
+	(nbsd_nat_target::thread_name): Likewise.
+	(nbsd_add_threads): Likewise.
+	(update_thread_list::post_attach): Likewise.
+	(nbsd_nat_target::update_thread_list): Likewise.
+	(post_attach::pid_to_str): Likewise.
+
 2020-03-25  Tom Tromey  <tom@tromey.com>

 	* compile/compile-object-load.c (get_out_value_type): Mention
diff --git a/gdb/nbsd-nat.c b/gdb/nbsd-nat.c
index 326bbe3aec3..556e146ab23 100644
--- a/gdb/nbsd-nat.c
+++ b/gdb/nbsd-nat.c
@@ -20,6 +20,8 @@
 #include "defs.h"

 #include "nbsd-nat.h"
+#include "gdbthread.h"
+#include "inferior.h"

 #include <sys/types.h>
 #include <sys/ptrace.h>
@@ -39,3 +41,162 @@ nbsd_nat_target::pid_to_exec_file (int pid)
     return NULL;
   return buf;
 }
+
+/* Generic thread (LWP) lister within a specified process.  The callback
+   parameters is a C++ function that is called for each detected thread.  */
+
+static void
+nbsd_thread_lister (const pid_t pid,
+		    std::function<bool (const struct kinfo_lwp *)> callback)
+{
+  int mib[5] = {CTL_KERN, KERN_LWP, pid, sizeof (struct kinfo_lwp), 0};
+  size_t size;
+
+  if (sysctl (mib, ARRAY_SIZE (mib), NULL, &size, NULL, 0) == -1 || size == 0)
+    perror_with_name (("sysctl"));
+
+  mib[4] = size / sizeof (size_t);
+
+  gdb::unique_xmalloc_ptr<struct kinfo_lwp> kl
+    ((struct kinfo_lwp *) xcalloc (size, 1));
+  if (kl == NULL)
+    perror_with_name (("calloc"));
+
+  if (sysctl (mib, ARRAY_SIZE (mib), kl.get (), &size, NULL, 0) == -1 ||
+      size == 0)
+    perror_with_name (("sysctl"));
+
+  for (size_t i = 0; i < size / sizeof (struct kinfo_lwp); i++)
+    {
+      struct kinfo_lwp *l = &kl.get ()[i];
+
+      /* Return true if the specified thread is alive.  */
+      auto lwp_alive =
+	[&l]()
+	{
+	  switch (kl->l_stat)
+	    {
+	    case LSSLEEP:
+	    case LSRUN:
+	    case LSONPROC:
+	    case LSSTOP:
+	    case LSSUSPENDED:
+	      return true;
+	    default:
+	      return false;
+	    }
+	};
+
+      /* Ignore embryonic or demised threads.  */
+      if (!lwp_alive (l))
+	continue;
+
+      if (callback (l))
+	break;
+    }
+}
+
+/* Return true if PTID is still active in the inferior.  */
+
+bool
+nbsd_nat_target::thread_alive (ptid_t ptid)
+{
+  pid_t pid = ptid.pid ();
+  int lwp = ptid.lwp ();
+  bool found = false;
+
+  auto fn =
+    [&lwp, &found] (const struct kinfo_lwp *kl)
+    {
+      if (kl->l_lid == lwp)
+	{
+	  found = true;
+	  return true;
+	}
+      return false;
+    };
+
+  nbsd_thread_lister (pid, fn);
+
+  return found;
+}
+
+/* Return the name assigned to a thread by an application.  Returns
+   the string in a static buffer.  */
+
+const char *
+nbsd_nat_target::thread_name (struct thread_info *thr)
+{
+  ptid_t ptid = thr->ptid;
+  pid_t pid = ptid.pid ();
+  int lwp = ptid.lwp ();
+
+  static char buf[KI_LNAMELEN] = {};
+
+  auto fn =
+    [&lwp] (const struct kinfo_lwp *kl)
+    {
+      if (kl->l_lid == lwp)
+	{
+	  xsnprintf (buf, sizeof buf, "%s", kl->l_name);
+	  return true;
+	}
+      return false;
+    };
+
+  nbsd_thread_lister (pid, fn);
+
+  return buf;
+}
+
+/* Implement the "post_attach" target_ops method.  */
+
+static void
+nbsd_add_threads (nbsd_nat_target *target, pid_t pid)
+{
+  auto fn =
+    [&target, &pid] (const struct kinfo_lwp *kl)
+    {
+      ptid_t ptid = ptid_t (pid, kl->l_lid, 0);
+      fprintf_unfiltered (gdb_stdlog, "NLWP: pid=%d lwp=%d\n", pid, kl->l_lid);
+      if (!in_thread_list (target, ptid))
+	{
+	  if (inferior_ptid.lwp () == 0)
+	    thread_change_ptid (target, inferior_ptid, ptid);
+	  else
+	    add_thread (target, ptid);
+	}
+      return false;
+    };
+
+  nbsd_thread_lister (pid, fn);
+}
+
+/* Implement the "post_attach" target_ops method.  */
+
+void
+nbsd_nat_target::post_attach (int pid)
+{
+  nbsd_add_threads (this, pid);
+}
+
+/* Implement the "update_thread_list" target_ops method.  */
+
+void
+nbsd_nat_target::update_thread_list ()
+{
+  prune_threads ();
+
+  nbsd_add_threads (this, inferior_ptid.pid ());
+}
+
+/* Convert PTID to a string.  */
+
+std::string
+nbsd_nat_target::pid_to_str (ptid_t ptid)
+{
+  pid_t pid = ptid.pid ();
+  int lwp = ptid.lwp ();
+
+  return string_printf ("LWP %d of process %d", lwp, pid);
+}
diff --git a/gdb/nbsd-nat.h b/gdb/nbsd-nat.h
index a752fbe572d..3606048cd07 100644
--- a/gdb/nbsd-nat.h
+++ b/gdb/nbsd-nat.h
@@ -22,11 +22,19 @@

 #include "inf-ptrace.h"

+struct thread_info;
+
 /* A prototype NetBSD target.  */

 struct nbsd_nat_target : public inf_ptrace_target
 {
   char *pid_to_exec_file (int pid) override;
+
+  bool thread_alive (ptid_t ptid) override;
+  const char *thread_name (struct thread_info *thr) override;
+  void post_attach (int pid) override;
+  void update_thread_list () override;
+  std::string pid_to_str (ptid_t ptid) override;
 };

 #endif /* nbsd-nat.h */
--
2.25.0