[PATCH] Update btrace data in maintenance btrace commands

["Stephen Röttger" <sroettger@google.com>]

From: Stephen Roettger <sroettger@google.com>

When calling `maintenance btrace packet-history` or `maintenance info btrace`,
the commands wouldn't show any data unless it was updated previously by some
other means, for example by running `info record`.
To fix this, use the require_btrace function from record-brace.h which
will update the data before returning the btrace_thread_info pointer.

Here's an example of the issue:
```
$ gdb -nx /usr/bin/ls
(gdb) break malloc
Breakpoint 1 at 0x46c8
(gdb) run
Starting program: /usr/bin/ls 

Breakpoint 1, 0x00007ffff7fec240 in malloc () from /lib64/ld-linux-x86-64.so.2
(gdb) record btrace bts
(gdb) c
Continuing.

Breakpoint 1, 0x00007ffff7fec240 in malloc () from /lib64/ld-linux-x86-64.so.2
(gdb) maintenance btrace packet-history 
No trace.
(gdb) maintenance info btrace 
Format: Branch Trace Store.
Aborted
```

gdb/ChangeLog:

        * btrace.c (maint_btrace_packet_history_cmd): use require_btrace
        (maint_info_btrace_cmd): use require_btrace
        * record-btrace.c (struct btrace_thread_info): mark non-static
        * record-btrace.h (require_btrace): export function

---
 gdb/btrace.c        | 13 ++-----------
 gdb/record-btrace.c |  2 +-
 gdb/record-btrace.h |  7 +++++++
 3 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/gdb/btrace.c b/gdb/btrace.c
index c697f37f46c..177e818f0cf 100644
--- a/gdb/btrace.c
+++ b/gdb/btrace.c
@@ -3231,12 +3231,8 @@ maint_btrace_packet_history_cmd (const char *arg, int from_tty)
   struct btrace_thread_info *btinfo;
   unsigned int size, begin, end, from, to;
 
-  thread_info *tp = find_thread_ptid (current_inferior (), inferior_ptid);
-  if (tp == NULL)
-    error (_("No thread."));
-
+  btinfo = require_btrace ();
   size = 10;
-  btinfo = &tp->btrace;
 
   btrace_maint_update_packets (btinfo, &begin, &end, &from, &to);
   if (begin == end)
@@ -3372,12 +3368,7 @@ maint_info_btrace_cmd (const char *args, int from_tty)
   if (args != NULL && *args != 0)
     error (_("Invalid argument."));
 
-  if (inferior_ptid == null_ptid)
-    error (_("No thread."));
-
-  thread_info *tp = inferior_thread ();
-
-  btinfo = &tp->btrace;
+  btinfo = require_btrace ();
 
   conf = btrace_conf (btinfo);
   if (conf == NULL)
diff --git a/gdb/record-btrace.c b/gdb/record-btrace.c
index b7b3c91f85d..79a6e47a4a6 100644
--- a/gdb/record-btrace.c
+++ b/gdb/record-btrace.c
@@ -269,7 +269,7 @@ require_btrace_thread (void)
    Throws an error if there is no thread or no trace.  This function never
    returns NULL.  */
 
-static struct btrace_thread_info *
+struct btrace_thread_info *
 require_btrace (void)
 {
   struct thread_info *tp;
diff --git a/gdb/record-btrace.h b/gdb/record-btrace.h
index 8e7bbd90e60..b56e720e5a5 100644
--- a/gdb/record-btrace.h
+++ b/gdb/record-btrace.h
@@ -29,4 +29,11 @@ extern void record_btrace_push_target (void);
    NULL if the cpu was configured as auto.  */
 extern const struct btrace_cpu *record_btrace_get_cpu (void);
 
+/* Update the branch trace for the current thread and return a pointer to its
+   branch trace information struct.
+
+   Throws an error if there is no thread or no trace.  This function never
+   returns NULL.  */
+extern struct btrace_thread_info * require_btrace (void);
+
 #endif /* RECORD_BTRACE_H */
-- 
2.31.1.295.g9ea45b61b8-goog