[PATCH v2] Implement basic threading support in the NetBSD target

Kamil Rytarowski
2020-03-26T03:18:06Z

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 | 166 +++++++++++++++++++++++++++++++++++++++++++++++++
gdb/nbsd-nat.h | 8 +++
3 files changed, 191 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..945699ccfbe 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 +41,167 @@ 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 (l->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 ())
+ 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);
+ 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)
+{
+ int lwp = ptid.lwp ();
+
+ if (lwp != 0)
+ {
+ pid_t pid = ptid.pid ();
+
+ return string_printf ("LWP %d of process %d", lwp, pid);
+ }
+
+ return normal_pid_to_str (ptid);
+}
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