Implement basic threading support in the NetBSD target

Message ID 20200326025314.2392-1-n54@gmx.com
State Superseded
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Series
  • Implement basic threading support in the NetBSD target
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Commit Message

Kamil Rytarowski March 26, 2020, 2:53 a.m.
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(+)

--
2.25.0

Comments

Tom Tromey April 1, 2020, 8:43 p.m. | #1
>>>>> "Kamil" == Kamil Rytarowski <n54@gmx.com> writes:


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

Thank you for the patch.

Kamil> +static void
Kamil> +nbsd_thread_lister (const pid_t pid,
Kamil> +		    std::function<bool (const struct kinfo_lwp *)> callback)

Perhaps a const reference here would be better.
Or maybe gdb::function_view, I'm not sure.

Kamil> +      /* Return true if the specified thread is alive.  */
Kamil> +      auto lwp_alive =
Kamil> +	[&l]()
Kamil> +	{
Kamil> +	  switch (kl->l_stat)
Kamil> +	    {
Kamil> +	    case LSSLEEP:
Kamil> +	    case LSRUN:
Kamil> +	    case LSONPROC:
Kamil> +	    case LSSTOP:
Kamil> +	    case LSSUSPENDED:
Kamil> +	      return true;
Kamil> +	    default:
Kamil> +	      return false;
Kamil> +	    }
Kamil> +	};
Kamil> +
Kamil> +      /* Ignore embryonic or demised threads.  */
Kamil> +      if (!lwp_alive (l))
Kamil> +	continue;

I don't think a lambda is needed here.

Kamil> +bool
Kamil> +nbsd_nat_target::thread_alive (ptid_t ptid)
Kamil> +{
Kamil> +  pid_t pid = ptid.pid ();
Kamil> +  int lwp = ptid.lwp ();
Kamil> +  bool found = false;
Kamil> +
Kamil> +  auto fn =
Kamil> +    [&lwp, &found] (const struct kinfo_lwp *kl)
Kamil> +    {
Kamil> +      if (kl->l_lid == lwp)
Kamil> +	{
Kamil> +	  found = true;
Kamil> +	  return true;
Kamil> +	}
Kamil> +      return false;
Kamil> +    };
Kamil> +
Kamil> +  nbsd_thread_lister (pid, fn);
Kamil> +
Kamil> +  return found;

A classic pattern in gdb is to have one of these iteration functions
(here, nbsd_thread_lister) return bool and have it return true if any
callback returns true, and false otherwise.

That would eliminate this "found" variable.

Kamil> +const char *
Kamil> +nbsd_nat_target::thread_name (struct thread_info *thr)
Kamil> +{
Kamil> +  static char buf[KI_LNAMELEN] = {};
...
Kamil> +  return buf;

This should return NULL if no name was found.
The above bool return would make this easy as well.

Kamil> +      fprintf_unfiltered (gdb_stdlog, "NLWP: pid=%d lwp=%d\n", pid, kl->l_lid);

This line should be removed.

Tom
Kamil Rytarowski April 1, 2020, 9:39 p.m. | #2
On 01.04.2020 22:43, Tom Tromey wrote:
>>>>>> "Kamil" == Kamil Rytarowski <n54@gmx.com> writes:

>

> Kamil> Use sysctl(3) as the portable interface to prompt NetBSD threads on

> Kamil> all supported NetBSD versions. In future newer versions could switch

> Kamil> to PT_LWPSTATUS ptrace(2) API that will be supported on NetBSD 10.0

> Kamil> and newer.

>

> Thank you for the patch.

>

> Kamil> +static void

> Kamil> +nbsd_thread_lister (const pid_t pid,

> Kamil> +		    std::function<bool (const struct kinfo_lwp *)> callback)

>

> Perhaps a const reference here would be better.

> Or maybe gdb::function_view, I'm not sure.

>


I've switched to gdb::function_view.

> Kamil> +      /* Return true if the specified thread is alive.  */

> Kamil> +      auto lwp_alive =

> Kamil> +	[&l]()

> Kamil> +	{

> Kamil> +	  switch (kl->l_stat)

> Kamil> +	    {

> Kamil> +	    case LSSLEEP:

> Kamil> +	    case LSRUN:

> Kamil> +	    case LSONPROC:

> Kamil> +	    case LSSTOP:

> Kamil> +	    case LSSUSPENDED:

> Kamil> +	      return true;

> Kamil> +	    default:

> Kamil> +	      return false;

> Kamil> +	    }

> Kamil> +	};

> Kamil> +

> Kamil> +      /* Ignore embryonic or demised threads.  */

> Kamil> +      if (!lwp_alive (l))

> Kamil> +	continue;

>

> I don't think a lambda is needed here.

>


I like lambda here as it matches the internals of the kernel behavior
here. Normally, I would add a local lwp_alive() helper function, but as
it is not needed anywhere else, I added it as a local inline lambda
function.

Using lambda a little bit simplifies the code as I can avoid "break"
that is nested inside for() and switch(). I could rewrite the code, but
in the current form it nicer reflects the NetBSD kernel.

PT_LWPSTATUS/PT_LWPNEXT would have implied lwp_alive().

> Kamil> +bool

> Kamil> +nbsd_nat_target::thread_alive (ptid_t ptid)

> Kamil> +{

> Kamil> +  pid_t pid = ptid.pid ();

> Kamil> +  int lwp = ptid.lwp ();

> Kamil> +  bool found = false;

> Kamil> +

> Kamil> +  auto fn =

> Kamil> +    [&lwp, &found] (const struct kinfo_lwp *kl)

> Kamil> +    {

> Kamil> +      if (kl->l_lid == lwp)

> Kamil> +	{

> Kamil> +	  found = true;

> Kamil> +	  return true;

> Kamil> +	}

> Kamil> +      return false;

> Kamil> +    };

> Kamil> +

> Kamil> +  nbsd_thread_lister (pid, fn);

> Kamil> +

> Kamil> +  return found;

>

> A classic pattern in gdb is to have one of these iteration functions

> (here, nbsd_thread_lister) return bool and have it return true if any

> callback returns true, and false otherwise.

>

> That would eliminate this "found" variable.

>


Done.

> Kamil> +const char *

> Kamil> +nbsd_nat_target::thread_name (struct thread_info *thr)

> Kamil> +{

> Kamil> +  static char buf[KI_LNAMELEN] = {};

> ...

> Kamil> +  return buf;

>

> This should return NULL if no name was found.

> The above bool return would make this easy as well.

>


Done.

> Kamil> +      fprintf_unfiltered (gdb_stdlog, "NLWP: pid=%d lwp=%d\n", pid, kl->l_lid);

>

> This line should be removed.

>


It was fixed in v2.

> Tom

>


Please review:

[PATCH v4] Implement basic threading support in the NetBSD target

Patch

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 */