[PATCH v4 01/11] Don't attempt to find TLS address when target has no registers

[Kevin Buettner <kevinb@redhat.com>]

This commit fixes two bugs, one of which is Bug 25807 - that one is
fixed by the change in findvar.c.  I found it while testing on aarch64;
it turned a KFAIL for gdb.threads/tls.exp: print a_thread_local
into a FAIL due to a GDB internal error.  In addition to the existing
test just noted, I've also added a test to the new test case
gdb.base/tls-nothreads.exp.  It'll be tested, using different
scenarios, up to 8 times:

PASS: gdb.base/tls-nothreads.exp: default: force_internal_tls=false: after exit: print tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: default: force_internal_tls=true: after exit: print tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: static: force_internal_tls=false: after exit: print tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: static: force_internal_tls=true: after exit: print tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: pthreads: force_internal_tls=false: after exit: print tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: pthreads: force_internal_tls=true: after exit: print tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: pthreads-static: force_internal_tls=false: after exit: print tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: pthreads-static: force_internal_tls=true: after exit: print tls_tbss_1

There is a related problem that's fixed by the minsyms.c change.  It
can be observed when debugging a program without debugging symbols
when the program is not executing.  I've written a new test for this,
but it's included in the new test case gdb.base/tls-nothreads.exp,
found later in this series.  Depending on the target, it'll be run
up to 8 times for different targets.  E.g., on aarch64, I'm seeing
these PASSes, all of which test this change:

PASS: gdb.base/tls-nothreads.exp: default: force_internal_tls=false: stripped: after exit: print (int) tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: default: force_internal_tls=true: stripped: after exit: print (int) tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: static: force_internal_tls=false: stripped: after exit: print (int) tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: static: force_internal_tls=true: stripped: after exit: print (int) tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: pthreads: force_internal_tls=false: stripped: after exit: print (int) tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: pthreads: force_internal_tls=true: stripped: after exit: print (int) tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: pthreads-static: force_internal_tls=false: stripped: after exit: print (int) tls_tbss_1
PASS: gdb.base/tls-nothreads.exp: pthreads-static: force_internal_tls=true: stripped: after exit: print (int) tls_tbss_1

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=25807
---
 gdb/findvar.c | 7 ++++++-
 gdb/minsyms.c | 8 +++++++-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/gdb/findvar.c b/gdb/findvar.c
index f7760aa61ca..a530e679c8a 100644
--- a/gdb/findvar.c
+++ b/gdb/findvar.c
@@ -485,7 +485,12 @@ language_defn::read_var_value (struct symbol *var,
 	/* Determine address of TLS variable. */
 	if (obj_section
 	    && (obj_section->the_bfd_section->flags & SEC_THREAD_LOCAL) != 0)
-	  addr = target_translate_tls_address (obj_section->objfile, addr);
+	  {
+	    if (!target_has_registers ())
+	      error (_("Cannot read `%s' without registers"),
+		     var->print_name ());
+	    addr = target_translate_tls_address (obj_section->objfile, addr);
+	  }
       }
       break;
 
diff --git a/gdb/minsyms.c b/gdb/minsyms.c
index 33eb9072e5f..a904bd96045 100644
--- a/gdb/minsyms.c
+++ b/gdb/minsyms.c
@@ -1684,7 +1684,13 @@ find_minsym_type_and_address (minimal_symbol *msymbol,
     {
       /* Skip translation if caller does not need the address.  */
       if (address_p != NULL)
-	*address_p = target_translate_tls_address (objfile, addr);
+	{
+	  if (!target_has_registers ())
+	    error (_(
+	      "Cannot determine address of TLS symbol `%s' without registers"),
+	      bound_msym.minsym->print_name ());
+	  *address_p = target_translate_tls_address (objfile, addr);
+	}
       return builtin_type (objfile)->nodebug_tls_symbol;
     }
 
-- 
2.46.2