[PATCH 00/28] Decouple inferior_ptid/inferior_thread(); dup ptids in thread list (PR/25412)

Pedro Alves
2020-04-14T17:54:38Z

In PR/25412, Simon noticed that after the multi-target series, the
tid-reuse.exp testcase manages to create a duplicate thread in the
thread list. Or rather, two threads with the same PTID.

This in turn exposes a design problem in GDB. The inferior_thread()
function looks up the current thread based on inferior_ptid:

struct thread_info*
inferior_thread (void)
{
struct thread_info *tp = find_thread_ptid (current_inferior (), inferior_ptid);
gdb_assert (tp);
return tp;
}

But if there can be more than one thread in the thread list with the
same ptid_t, inferior_thread() may well return the wrong thread.

This series fixes this by making the current thread be a global
thread_info pointer that is written to directly by switch_to_thread,
etc., and making inferior_thread() return that pointer, instead of
having inferior_thread() lookup up the inferior_ptid thread, by
ptid_t. You can look at this as a continuation of the effort of using
more thread_info pointers instead of ptids when possible.

This change required auditing the whole codebase for places where we
were writing to inferior_ptid directly to change the current thread,
and change them to use switch_to_thread instead or one of its
siblings, because otherwise inferior_thread() and inferior_ptid would
get out of sync and inferior_thread() would return a thread unrelated
to the new inferior_ptid we wanted to switch to. That was all
(hopefully) done in all the patches leading up to the last one.

After this, inferior_ptid still exists, but it is mostly read-only and
mainly used by target backend code. It is also relied on by a number
of target methods as a global input argument. E.g., the target_resume
interface and the memory reading routines -- we still need it there
because we need to be able to access memory off of processes for which
we don't have a corresponding inferior/thread object, like when
handling forks. Maybe we could pass down a context explicitly to
target_read_memory, etc.

Most of the host-/native-specific code here is untested. I did my
best, but I won't be surprised if more tweaking is necessary.

Testing on native x86_64 GNU/Linux is regression free for me. Testing
against gdbserver has regressed significantly in the past months and
is becoming difficult to run with a high number of long timeout
sequences; really looks like people aren't paying much attention to
that. I think this series doesn't regress gdbserver, but it's getting
hard to tell. :-/

Pedro Alves (28):
Don't write to inferior_ptid in linux_get_siginfo_data
gcore, handle exited threads better
Refactor delete_program_space as a destructor
Don't write to inferior_ptid in gdbarch-selftests.c, mock
address_space too
Don't write to inferior_ptid in inf-ptrace.c
Don't write to inferior_ptid in target.c
Don't write to inferior_ptid in infrun.c
Don't write to inferior_ptid in procfs.c
Don't write to inferior_ptid in tracefile-tfile.c
Don't write to inferior_ptid in tracectf.c
Don't write to inferior_ptid in remote.c
Don't write to inferior_ptid in remote-sim.c
Don't write to inferior_ptid in nto-procfs.c
Don't write to inferior_ptid in go32-nat.c
Don't write to inferior_ptid in gnu-nat.c
Don't write to inferior_ptid in darwin-nat.c
Don't write to inferior_ptid in corelow.c
Don't write to inferior_ptid in bsd-kvm.c
Don't write to inferior_ptid in btrace_fetch
Don't write to inferior_ptid in bsd-kvm.c
Don't write to inferior_ptid in fork-child.c
Don't write to inferior_ptid in go32-nat.c
Don't write to inferior_ptid in remote-sim.c
Don't write to inferior_ptid in windows-nat.c, part I
Don't write to inferior_ptid in windows-nat.c, part II
Don't write to inferior_ptid in ravenscar-thread.c
Don't write to inferior_ptid in aix-thread.c
Decouple inferior_ptid/inferior_thread(); dup ptids in thread list
(PR/25412)

gdb/aix-thread.c | 2 +-
gdb/bsd-kvm.c | 6 +--
gdb/btrace.c | 6 ---
gdb/corelow.c | 20 +++++-----
gdb/darwin-nat.c | 16 ++++----
gdb/fork-child.c | 3 --
gdb/gdbarch-selftests.c | 17 ++++----
gdb/gdbthread.h | 17 ++++----
gdb/gnu-nat.c | 14 +++----
gdb/go32-nat.c | 8 +---
gdb/inf-ptrace.c | 19 +++++----
gdb/inferior.c | 2 +-
gdb/infrun.c | 101 +++++++++++++++++++-----------------------------
gdb/linux-tdep.c | 64 ++++++++++++++++--------------
gdb/nat/windows-nat.c | 1 -
gdb/nat/windows-nat.h | 3 --
gdb/nto-procfs.c | 24 ++++++------
gdb/procfs.c | 18 ++++-----
gdb/progspace.c | 79 ++++++++++++++++++++-----------------
gdb/progspace.h | 4 --
gdb/ravenscar-thread.c | 49 ++++++++++++-----------
gdb/remote-sim.c | 10 ++---
gdb/remote.c | 34 ++++++++--------
gdb/target.c | 2 +-
gdb/thread.c | 97 ++++++++++++++++------------------------------
gdb/tracectf.c | 7 ++--
gdb/tracefile-tfile.c | 7 ++--
gdb/windows-nat.c | 68 +++++++++++++++-----------------
28 files changed, 315 insertions(+), 383 deletions(-)

base-commit: dd1cab0694592099854e66467319253954c93764
--
2.14.5