Re: [PATCH 19/28] Don't write to inferior_ptid in btrace_fetch

[Pedro Alves <palves@redhat.com>]

On 4/15/20 5:52 AM, Metzger, Markus T via Gdb-patches wrote:
> Hello Pedro,
> 
>> AFAICT, this isn't required nowadays.
> 
> How is this working nowadays?  There are still references to inferior_ptid.

Clearly I didn't think this one through.  I put a tp->ptid==inferior_ptid
assertion in place, and that regressed gdb.python/py-record-btrace-threads.exp.
This should mean that the target_read_btrace calls in btrace_fetch can hit
the wrong thread.

So here's an alternative patch.  No regressions when tested with:

 $ make check TESTS="gdb.btrace/*.exp */*btrace*.exp"

From 92c8fa469295b5737e6cb5e882024af2e9872c4c Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Mon, 13 Apr 2020 20:02:22 +0100
Subject: [PATCH 19/28] Don't write to inferior_ptid in btrace.c

gdb/ChangeLog:
yyyy-mm-dd  Pedro Alves  <palves@redhat.com>

	* btrace.c (btrace_fetch): Use switch_to_thread instead of writing
	to inferior_ptid.
---
 gdb/btrace.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/gdb/btrace.c b/gdb/btrace.c
index bbf8749649..2964455680 100644
--- a/gdb/btrace.c
+++ b/gdb/btrace.c
@@ -1908,13 +1908,13 @@ btrace_fetch (struct thread_info *tp, const struct btrace_cpu *cpu)
   if (btinfo->replay != NULL)
     return;
 
-  /* With CLI usage, TP->PTID always equals INFERIOR_PTID here.  Now that we
-     can store a gdb.Record object in Python referring to a different thread
-     than the current one, temporarily set INFERIOR_PTID.  */
-  scoped_restore save_inferior_ptid = make_scoped_restore (&inferior_ptid);
-  inferior_ptid = tp->ptid;
+  /* With CLI usage, TP is always the current thread when we get here.
+     However, since we can also store a gdb.Record object in Python
+     referring to a different thread than the current one, we need to
+     temporarily set the current thread.  */
+  scoped_restore_current_thread restore_thread;
+  switch_to_thread (tp);
 
   /* We should not be called on running or exited threads.  */
   gdb_assert (can_access_registers_thread (tp));

-- 
2.14.5