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From: "simark at simark dot ca" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug record/28086] inferior.c:303: internal-error: inferior*
 find_inferior _pid(process_stratum_target*, int): Assertion `pid != 0'
 failed.
Date: Wed, 14 Jul 2021 14:41:48 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D28086

--- Comment #4 from Simon Marchi <simark at simark dot ca> ---
I didn't manage to reproduce:

  # of expected passes            7

At frame 42, we have the new_thread observable being fired, because a new
thread is being added.  When the new_thread observable, I don't think there=
 is
any guarantee about the global context, value of inferior_ptid and all.

btrace_compute_ftrace_bts at frame 32 is the last frame where we know the
thread we are working on.  It then calls gdb_insn_length which eventually c=
alls
target_read.  So from gdb_insn_length and on, inferior_ptid and the rest of=
 the
global context should be set appropriately.  I think that
btrace_compute_ftrace_bts should set and restore the current thread (ideall=
y,
it should pass down the thread, but that's for another day).

Here's an untested patch (well, I tested it, the test still passes for me, =
but
I don't know if it fixes your regression):

diff --git a/gdb/btrace.c b/gdb/btrace.c
index 5e689c11d4bd..93e7bc438a7e 100644
--- a/gdb/btrace.c
+++ b/gdb/btrace.c
@@ -1104,6 +1104,11 @@ btrace_compute_ftrace_bts (struct thread_info *tp,
          size =3D 0;
          try
            {
+             /* gdb_insn_length will need to read memory from TP, which may
+                not be the current thread on entryt.  Make sure it is.  */
+             scoped_restore_current_thread restore_thread;
+             switch_to_thread (tp);
+
              size =3D gdb_insn_length (gdbarch, pc);
            }
          catch (const gdb_exception_error &error)

--=20
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