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, 15 insertions, 56 deletions

diff --git a/gdb/regcache.c b/gdb/regcache.c
index 6a4359d..4ebb8cb 100644
--- a/gdb/regcache.c
+++ b/gdb/regcache.c
@@ -22,6 +22,7 @@
 #include "gdbthread.h"
 #include "target.h"
 #include "test-target.h"
+#include "scoped-mock-context.h"
 #include "gdbarch.h"
 #include "gdbcmd.h"
 #include "regcache.h"
@@ -1596,49 +1597,7 @@ public:
 static void
 cooked_read_test (struct gdbarch *gdbarch)
 {
-  /* Error out if debugging something, because we're going to push the
-     test target, which would pop any existing target.  */
-  if (current_top_target ()->stratum () >= process_stratum)
-    error (_("target already pushed"));
-
-  /* Create a mock environment.  An inferior with a thread, with a
-     process_stratum target pushed.  */
-
-  target_ops_no_register mock_target;
-  ptid_t mock_ptid (1, 1);
-  inferior mock_inferior (mock_ptid.pid ());
-  address_space mock_aspace {};
-  mock_inferior.gdbarch = gdbarch;
-  mock_inferior.aspace = &mock_aspace;
-  thread_info mock_thread (&mock_inferior, mock_ptid);
-  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);
-  inferior_list = &mock_inferior;
-
-  /* Switch to the mock inferior.  */
-  scoped_restore_current_inferior restore_current_inferior;
-  set_current_inferior (&mock_inferior);
-
-  /* Push the process_stratum target so we can mock accessing
-     registers.  */
-  push_target (&mock_target);
-
-  /* Pop it again on exit (return/exception).  */
-  struct on_exit
-  {
-    ~on_exit ()
-    {
-      pop_all_targets_at_and_above (process_stratum);
-    }
-  } pop_targets;
-
-  /* Switch to the mock thread.  */
-  scoped_restore restore_inferior_ptid
-    = make_scoped_restore (&inferior_ptid, mock_ptid);
+  scoped_mock_context<target_ops_no_register> mockctx (gdbarch);
 
   /* Test that read one raw register from regcache_no_target will go
      to the target layer.  */
@@ -1653,21 +1612,21 @@ cooked_read_test (struct gdbarch *gdbarch)
 	break;
     }
 
-  readwrite_regcache readwrite (&mock_target, gdbarch);
+  readwrite_regcache readwrite (&mockctx.mock_target, gdbarch);
   gdb::def_vector<gdb_byte> buf (register_size (gdbarch, nonzero_regnum));
 
   readwrite.raw_read (nonzero_regnum, buf.data ());
 
   /* raw_read calls target_fetch_registers.  */
-  SELF_CHECK (mock_target.fetch_registers_called > 0);
-  mock_target.reset ();
+  SELF_CHECK (mockctx.mock_target.fetch_registers_called > 0);
+  mockctx.mock_target.reset ();
 
   /* Mark all raw registers valid, so the following raw registers
      accesses won't go to target.  */
   for (auto i = 0; i < gdbarch_num_regs (gdbarch); i++)
     readwrite.raw_update (i);
 
-  mock_target.reset ();
+  mockctx.mock_target.reset ();
   /* Then, read all raw and pseudo registers, and don't expect calling
      to_{fetch,store}_registers.  */
   for (int regnum = 0; regnum < gdbarch_num_cooked_regs (gdbarch); regnum++)
@@ -1680,18 +1639,18 @@ cooked_read_test (struct gdbarch *gdbarch)
       SELF_CHECK (REG_VALID == readwrite.cooked_read (regnum,
 						      inner_buf.data ()));
 
-      SELF_CHECK (mock_target.fetch_registers_called == 0);
-      SELF_CHECK (mock_target.store_registers_called == 0);
-      SELF_CHECK (mock_target.xfer_partial_called == 0);
+      SELF_CHECK (mockctx.mock_target.fetch_registers_called == 0);
+      SELF_CHECK (mockctx.mock_target.store_registers_called == 0);
+      SELF_CHECK (mockctx.mock_target.xfer_partial_called == 0);
 
-      mock_target.reset ();
+      mockctx.mock_target.reset ();
     }
 
   readonly_detached_regcache readonly (readwrite);
 
   /* GDB may go to target layer to fetch all registers and memory for
      readonly regcache.  */
-  mock_target.reset ();
+  mockctx.mock_target.reset ();
 
   for (int regnum = 0; regnum < gdbarch_num_cooked_regs (gdbarch); regnum++)
     {
@@ -1749,11 +1708,11 @@ cooked_read_test (struct gdbarch *gdbarch)
 	    }
 	}
 
-      SELF_CHECK (mock_target.fetch_registers_called == 0);
-      SELF_CHECK (mock_target.store_registers_called == 0);
-      SELF_CHECK (mock_target.xfer_partial_called == 0);
+      SELF_CHECK (mockctx.mock_target.fetch_registers_called == 0);
+      SELF_CHECK (mockctx.mock_target.store_registers_called == 0);
+      SELF_CHECK (mockctx.mock_target.xfer_partial_called == 0);
 
-      mock_target.reset ();
+      mockctx.mock_target.reset ();
     }
 }