[PATCH] btrace: avoid tp != NULL assertion

[Markus Metzger <markus dot t dot metzger at intel dot com>]

On some targets, I see the LWP field patched out of INFERIOR_PTID before
calling record_btrace_fetch_registers.  Looking to the respective linux-nat
versions, they use the PID field if the LWP field is zero.

Implement a similar behavior for record-btrace.

2015-02-09  Markus Metzger  <markus.t.metzger@intel.com>

gdb/
	* record-btrace.c (record_btrace_inferior_thread): New.
	(require_btrace_thread, record_btrace_info):
	(record_btrace_tailcall_frame_sniffer): Call
	record_btrace_inferior_thread.
	(record_btrace_fetch_registers, record_btrace_frame_sniffer):
	Call record_btrace_inferior_thread.  Replace tp != NULL assertion
	with error call.
---
 gdb/record-btrace.c | 45 ++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 38 insertions(+), 7 deletions(-)

diff --git a/gdb/record-btrace.c b/gdb/record-btrace.c
index 102e0eb..b7dedd9 100644
--- a/gdb/record-btrace.c
+++ b/gdb/record-btrace.c
@@ -97,6 +97,35 @@ static struct cmd_list_element *show_record_btrace_bts_cmdlist;
   while (0)
 
 
+/* Return a pointer to the thread_info of inferior_ptid.
+
+   In some cases, we see the LWP field of INFERIOR_PTID patched out.  Use the
+   PID as LWP similar to what i386|amd64_linux_fetch_inferior_registers do.  */
+
+static struct thread_info *
+record_btrace_inferior_thread (void)
+{
+  ptid_t ptid;
+  long lwp;
+
+  DEBUG ("inferior thread");
+
+  ptid = inferior_ptid;
+
+  /* GNU/Linux LWP ID's are process ID's.  */
+  lwp = ptid_get_lwp (ptid);
+  if (lwp == 0)
+    {
+      int pid;
+
+      /* Not a threaded program.  Use the PID as LWP ID.  */
+      pid = ptid_get_pid (ptid);
+      ptid = ptid_build (pid, pid, 0);
+    }
+
+  return find_thread_ptid (ptid);
+}
+
 /* Update the branch trace for the current thread and return a pointer to its
    thread_info.
 
@@ -110,7 +139,7 @@ require_btrace_thread (void)
 
   DEBUG ("require");
 
-  tp = find_thread_ptid (inferior_ptid);
+  tp = record_btrace_inferior_thread ();
   if (tp == NULL)
     error (_("No thread."));
 
@@ -370,7 +399,7 @@ record_btrace_info (struct target_ops *self)
 
   DEBUG ("info");
 
-  tp = find_thread_ptid (inferior_ptid);
+  tp = record_btrace_inferior_thread ();
   if (tp == NULL)
     error (_("No thread."));
 
@@ -1163,8 +1192,9 @@ record_btrace_fetch_registers (struct target_ops *ops,
   struct btrace_insn_iterator *replay;
   struct thread_info *tp;
 
-  tp = find_thread_ptid (inferior_ptid);
-  gdb_assert (tp != NULL);
+  tp = record_btrace_inferior_thread ();
+  if (tp == NULL)
+    error (_("No thread."));
 
   replay = tp->btrace.replay;
   if (replay != NULL && !record_btrace_generating_corefile)
@@ -1414,8 +1444,9 @@ record_btrace_frame_sniffer (const struct frame_unwind *self,
   struct frame_info *next;
 
   /* THIS_FRAME does not contain a reference to its thread.  */
-  tp = find_thread_ptid (inferior_ptid);
-  gdb_assert (tp != NULL);
+  tp = record_btrace_inferior_thread ();
+  if (tp == NULL)
+    error (_("No thread."));
 
   bfun = NULL;
   next = get_next_frame (this_frame);
@@ -1482,7 +1513,7 @@ record_btrace_tailcall_frame_sniffer (const struct frame_unwind *self,
 
   /* This is our frame.  Initialize the frame cache.  */
   cache = bfcache_new (this_frame);
-  cache->tp = find_thread_ptid (inferior_ptid);
+  cache->tp = record_btrace_inferior_thread ();
   cache->bfun = bfun;
 
   *this_cache = cache;
-- 
1.8.3.1