Fix "maint selftest" regression, add struct scoped_mock_context

This commit:

 commit 3922b302645fda04da42a5279399578ae2f6206c
 Author:     Pedro Alves <palves@redhat.com>
 AuthorDate: Thu Jun 18 21:28:37 2020 +0100

    Decouple inferior_ptid/inferior_thread(); dup ptids in thread list (PR 25412)

caused a regression for gdb.gdb/unittest.exp when GDB is configured
with --enable-targets=all.  The failure is:

  gdb/thread.c:95: internal-error: thread_info* inferior_thread(): Assertion `current_thread_ != nullptr' failed.

The problem is in this line in regcache.c:cooked_read_test:

  /* Switch to the mock thread.  */
  scoped_restore restore_inferior_ptid
    = make_scoped_restore (&inferior_ptid, mock_ptid);

Both gdbarch-selftest.c and regcache.c set up a similar mock context,
but the series the patch above belongs to only updated the
gdbarch-selftest.c context to not write to inferior_ptid directly, and
missed updating regcache.c's.

Instead of copying the fix over to regcache.c, share the mock context
setup code in a new RAII class, based on gdbarch-selftest.c's version.

Also remove the "target already pushed" error from regcache.c, like it
had been removed from gdbarch-selftest.c in the multi-target series.
That check is unnecessary because each inferior now has its own target
stack, and the unit test pushes a target on a separate (mock)
inferior, not the current inferior on entry.

gdb/ChangeLog:
2020-06-23  Pedro Alves  <palves@redhat.com>

	* gdbarch-selftests.c: Don't include inferior.h, gdbthread.h or
	progspace-and-thread.h.  Include scoped-mock-context.h instead.
	(register_to_value_test): Use scoped_mock_context.
	* regcache.c: Include "scoped-mock-context.h".
	(cooked_read_test): Don't error out if a target is already pushed.
	Use scoped_mock_context.  Adjust.
	* scoped-mock-context.h: New file.

1 files changed, 2 insertions, 37 deletions

diff --git a/gdb/gdbarch-selftests.c b/gdb/gdbarch-selftests.c
index 91aa9d8..4f9adbd 100644
--- a/gdb/gdbarch-selftests.c
+++ b/gdb/gdbarch-selftests.c
@@ -20,14 +20,12 @@
 #include "defs.h"
 #include "gdbsupport/selftest.h"
 #include "selftest-arch.h"
-#include "inferior.h"
-#include "gdbthread.h"
 #include "target.h"
 #include "test-target.h"
 #include "target-float.h"
 #include "gdbsupport/def-vector.h"
 #include "gdbarch.h"
-#include "progspace-and-thread.h"
+#include "scoped-mock-context.h"
 
 namespace selftests {
 
@@ -71,40 +69,7 @@ register_to_value_test (struct gdbarch *gdbarch)
       builtin->builtin_char32,
     };
 
-  /* Create a mock environment.  An inferior with a thread, with a
-     process_stratum target pushed.  */
-
-  test_target_ops mock_target;
-  ptid_t mock_ptid (1, 1);
-  program_space mock_pspace (new_address_space ());
-  inferior mock_inferior (mock_ptid.pid ());
-  mock_inferior.gdbarch = gdbarch;
-  mock_inferior.aspace = mock_pspace.aspace;
-  mock_inferior.pspace = &mock_pspace;
-  thread_info mock_thread (&mock_inferior, mock_ptid);
-
-  scoped_restore_current_pspace_and_thread restore_pspace_thread;
-
-  scoped_restore restore_thread_list
-    = make_scoped_restore (&mock_inferior.thread_list, &mock_thread);
-
-  /* Add the mock inferior to the inferior list so that look ups by
-     target+ptid can find it.  */
-  scoped_restore restore_inferior_list
-    = make_scoped_restore (&inferior_list, &mock_inferior);
-
-  /* Switch to the mock inferior.  */
-  switch_to_inferior_no_thread (&mock_inferior);
-
-  /* Push the process_stratum target so we can mock accessing
-     registers.  */
-  push_target (&mock_target);
-
-  /* Pop it again on exit (return/exception).  */
-  SCOPE_EXIT { pop_all_targets_at_and_above (process_stratum); };
-
-  /* Switch to the mock thread.  */
-  switch_to_thread (&mock_thread);
+  scoped_mock_context<test_target_ops> mockctx (gdbarch);
 
   struct frame_info *frame = get_current_frame ();
   const int num_regs = gdbarch_num_cooked_regs (gdbarch);