[PATCH 2/2] Don't lose language determined from the "main" name (fix gdb.ada/minsyms.exp)

[Pedro Alves <palves at redhat dot com>]

gdb.ada/minsyms.exp fails like this here:

 FAIL: gdb.ada/minsyms.exp: print integer(some_minsym)
 FAIL: gdb.ada/minsyms.exp: print /x integer(&some_minsym)

The problem is that if you have debug info for glibc, GDB switches the
current language to C before it reaches the program's entry point, and
then Ada's cast syntax doesn't work when the current language is C:

  print integer(some_minsym)
  A syntax error in expression, near `some_minsym)'.
  (gdb) FAIL: gdb.ada/minsyms.exp: print integer(some_minsym)

I first thought of doing "set language ada" in the testcase, but
looking deeper, I realized that before running to main, GDB knows the
program is Ada, determined by reading __gnat_ada_main_program_name,
via set_initial_language->main_language->find_main_name->
ada_main_name, and loses that when it is handling a shared library
event.  That looks like a bug to me.

gdb/testsuite/ChangeLog:
2017-11-21  Pedro Alves  <palves@redhat.com>

	* solib-svr4.c: Save/restore language around evaluating a probe
	argument.
---
 gdb/solib-svr4.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
index 5ec606d..e6f818a 100644
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -1936,6 +1936,21 @@ svr4_handle_solib_event (void)
   usm_chain = make_cleanup (resume_section_map_updates_cleanup,
 			    current_program_space);
 
+  /* Make sure evaluating probe arguments doesn't cause us to switch
+     the user's current language to the runtime's language.
+     Evaluating probe arguments relies on reading registers off the
+     selected frame.  When we're handling a shared library event, this
+     is going to be the first time we fetch the selected frame (as
+     opposed to the current frame), and if there's debug info for the
+     loader (e.g., glibc), this switches to its language (usually C).
+     Usually that ends up masked because we will usually next stop in
+     the main program (e.g., user did "start"), and switch to the
+     right language again then, if the program has debug info.
+     However, if the program does not have debug info, then GDB won't
+     switch, and we'd lose the language that was determined earlier by
+     sniffing the program's main name.  */
+  scoped_restore_current_language save_language;
+
   TRY
     {
       val = evaluate_probe_argument (pa->probe, 1, frame);
-- 
2.5.5