gdb: pass execing and following inferior to inferior_execd observers

The upcoming patch to support exec in the amd-dbgapi target needs to
detach amd-dbgapi from the inferior doing the exec and attach amd-dbgapi
to the inferior continuing the execution.  They may or may not be the
same, depending on the `set follow-exec-mode` setting.  But even if they
are the same, we need to do the detach / attach dance.

With the current observable signature, the observers only receive the
inferior in which execution continues (the "following" inferior).

Change the signature to pass both inferiors, and update all existing
observers.

Change-Id: I259d1ea09f70f43be739378d6023796f2fce2659
Reviewed-By: Pedro Alves <pedro@palves.net>

5 files changed, 52 insertions, 28 deletions

diff --git a/gdb/infrun.c b/gdb/infrun.c
index ba56fe3..e77ad31 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1293,7 +1293,8 @@ follow_exec (ptid_t ptid, const char *exec_file_target)
      previous incarnation of this process.  */
   no_shared_libraries (nullptr, 0);
 
-  struct inferior *inf = current_inferior ();
+  inferior *execing_inferior = current_inferior ();
+  inferior *following_inferior;
 
   if (follow_exec_mode_string == follow_exec_mode_new)
     {
@@ -1304,19 +1305,19 @@ follow_exec (ptid_t ptid, const char *exec_file_target)
 	 inferior's pid.  Having two inferiors with the same pid would confuse
 	 find_inferior_p(t)id.  Transfer the terminal state and info from the
 	  old to the new inferior.  */
-      inferior *new_inferior = add_inferior_with_spaces ();
-
-      swap_terminal_info (new_inferior, inf);
-      exit_inferior_silent (inf);
+      following_inferior = add_inferior_with_spaces ();
 
-      new_inferior->pid = pid;
-      target_follow_exec (new_inferior, ptid, exec_file_target);
+      swap_terminal_info (following_inferior, execing_inferior);
+      exit_inferior_silent (execing_inferior);
 
-      /* We continue with the new inferior.  */
-      inf = new_inferior;
+      following_inferior->pid = pid;
     }
   else
     {
+      /* follow-exec-mode is "same", we continue execution in the execing
+	 inferior.  */
+      following_inferior = execing_inferior;
+
       /* The old description may no longer be fit for the new image.
 	 E.g, a 64-bit process exec'ed a 32-bit process.  Clear the
 	 old description; we'll read a new one below.  No need to do
@@ -1324,18 +1325,20 @@ follow_exec (ptid_t ptid, const char *exec_file_target)
 	 around (its description is later cleared/refetched on
 	 restart).  */
       target_clear_description ();
-      target_follow_exec (inf, ptid, exec_file_target);
     }
 
-  gdb_assert (current_inferior () == inf);
-  gdb_assert (current_program_space == inf->pspace);
+  target_follow_exec (following_inferior, ptid, exec_file_target);
+
+  gdb_assert (current_inferior () == following_inferior);
+  gdb_assert (current_program_space == following_inferior->pspace);
 
   /* Attempt to open the exec file.  SYMFILE_DEFER_BP_RESET is used
      because the proper displacement for a PIE (Position Independent
      Executable) main symbol file will only be computed by
      solib_create_inferior_hook below.  breakpoint_re_set would fail
      to insert the breakpoints with the zero displacement.  */
-  try_open_exec_file (exec_file_host.get (), inf, SYMFILE_DEFER_BP_RESET);
+  try_open_exec_file (exec_file_host.get (), following_inferior,
+		      SYMFILE_DEFER_BP_RESET);
 
   /* If the target can specify a description, read it.  Must do this
      after flipping to the new executable (because the target supplied
@@ -1345,7 +1348,7 @@ follow_exec (ptid_t ptid, const char *exec_file_target)
      registers.  */
   target_find_description ();
 
-  gdb::observers::inferior_execd.notify (inf);
+  gdb::observers::inferior_execd.notify (execing_inferior, following_inferior);
 
   breakpoint_re_set ();
 
@@ -1622,15 +1625,15 @@ infrun_inferior_exit (struct inferior *inf)
 }
 
 static void
-infrun_inferior_execd (inferior *inf)
+infrun_inferior_execd (inferior *exec_inf, inferior *follow_inf)
 {
   /* If some threads where was doing a displaced step in this inferior at the
      moment of the exec, they no longer exist.  Even if the exec'ing thread
      doing a displaced step, we don't want to to any fixup nor restore displaced
      stepping buffer bytes.  */
-  inf->displaced_step_state.reset ();
+  follow_inf->displaced_step_state.reset ();
 
-  for (thread_info *thread : inf->threads ())
+  for (thread_info *thread : follow_inf->threads ())
     thread->displaced_step_state.reset ();
 
   /* Since an in-line step is done with everything else stopped, if there was
@@ -1638,7 +1641,7 @@ infrun_inferior_execd (inferior *inf)
      thread.  */
   clear_step_over_info ();
 
-  inf->thread_waiting_for_vfork_done = nullptr;
+  follow_inf->thread_waiting_for_vfork_done = nullptr;
 }
 
 /* If ON, and the architecture supports it, GDB will use displaced
diff --git a/gdb/jit.c b/gdb/jit.c
index e276b34..e085d56 100644
--- a/gdb/jit.c
+++ b/gdb/jit.c
@@ -1147,7 +1147,10 @@ jit_prepend_unwinder (struct gdbarch *gdbarch)
     }
 }
 
-/* Register any already created translations.  */
+/* Looks for the descriptor and registration symbols and breakpoints
+   the registration function.  If it finds both, it registers all the
+   already JITed code.  If it has already found the symbols, then it
+   doesn't try again.  */
 
 static void
 jit_inferior_init (inferior *inf)
@@ -1203,10 +1206,7 @@ jit_inferior_init (inferior *inf)
     }
 }
 
-/* Looks for the descriptor and registration symbols and breakpoints
-   the registration function.  If it finds both, it registers all the
-   already JITed code.  If it has already found the symbols, then it
-   doesn't try again.  */
+/* inferior_created observer.  */
 
 static void
 jit_inferior_created_hook (inferior *inf)
@@ -1214,6 +1214,14 @@ jit_inferior_created_hook (inferior *inf)
   jit_inferior_init (inf);
 }
 
+/* inferior_execd observer.  */
+
+static void
+jit_inferior_execd_hook (inferior *exec_inf, inferior *follow_inf)
+{
+  jit_inferior_init (follow_inf);
+}
+
 /* Exported routine to call to re-set the jit breakpoints,
    e.g. when a program is rerun.  */
 
@@ -1304,7 +1312,7 @@ _initialize_jit ()
 	   &maintenanceinfolist);
 
   gdb::observers::inferior_created.attach (jit_inferior_created_hook, "jit");
-  gdb::observers::inferior_execd.attach (jit_inferior_created_hook, "jit");
+  gdb::observers::inferior_execd.attach (jit_inferior_execd_hook, "jit");
   gdb::observers::inferior_exit.attach (jit_inferior_exit_hook, "jit");
   gdb::observers::breakpoint_deleted.attach (jit_breakpoint_deleted, "jit");
 
diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
index 1fc9cb6..b5eee5e 100644
--- a/gdb/linux-tdep.c
+++ b/gdb/linux-tdep.c
@@ -244,6 +244,14 @@ invalidate_linux_cache_inf (struct inferior *inf)
   linux_inferior_data.clear (inf);
 }
 
+/* inferior_execd observer.  */
+
+static void
+linux_inferior_execd (inferior *exec_inf, inferior *follow_inf)
+{
+  invalidate_linux_cache_inf (follow_inf);
+}
+
 /* Fetch the linux cache info for INF.  This function always returns a
    valid INFO pointer.  */
 
@@ -2789,7 +2797,7 @@ _initialize_linux_tdep ()
 					"linux-tdep");
   gdb::observers::inferior_appeared.attach (invalidate_linux_cache_inf,
 					    "linux-tdep");
-  gdb::observers::inferior_execd.attach (invalidate_linux_cache_inf,
+  gdb::observers::inferior_execd.attach (linux_inferior_execd,
 					 "linux-tdep");
 
   add_setshow_boolean_cmd ("use-coredump-filter", class_files,
diff --git a/gdb/observable.h b/gdb/observable.h
index efd0446..00955cb 100644
--- a/gdb/observable.h
+++ b/gdb/observable.h
@@ -90,8 +90,12 @@ extern observable<> executable_changed;
    information on the inferior has been printed.  */
 extern observable<inferior */* inferior */> inferior_created;
 
-/* The inferior INF has exec'ed a new executable file.  */
-extern observable<struct inferior */* inf */> inferior_execd;
+/* The inferior EXEC_INF has exec'ed a new executable file.
+
+   Execution continues in FOLLOW_INF, which may or may not be the same as
+   EXEC_INF, depending on "set follow-exec-mode".  */
+extern observable<inferior */* exec_inf */, inferior */* follow_inf */>
+    inferior_execd;
 
 /* The status of process record for inferior inferior in gdb has
    changed.  The process record is started if STARTED is true, and
diff --git a/gdb/solib.c b/gdb/solib.c
index 09bee49..1614783 100644
--- a/gdb/solib.c
+++ b/gdb/solib.c
@@ -1744,7 +1744,8 @@ _initialize_solib ()
 {
   gdb::observers::free_objfile.attach (remove_user_added_objfile,
 				       "solib");
-  gdb::observers::inferior_execd.attach ([] (inferior *inf)
+  gdb::observers::inferior_execd.attach ([] (inferior *exec_inf,
+					     inferior *follow_inf)
     {
       solib_create_inferior_hook (0);
     }, "solib");