[PATCH] Fixup gdb.python/py-value.exp for bare-metal aarch64-elf

[Luis Machado <lgustavo at codesourcery dot com>]

I noticed that testing aarch64-elf gdb with a physical board
ran into issues with gdb.python/py-value.exp. Further investigation showed
that we were actually trying to dereference a NULL pointer (argv) when trying
to access argv[0].

Being bare-metal, argv is not guaranteed to be there. So we need to make sure
argv is sane before accessing argv[0].

After fixing that, i noticed we were assuming a value of 1 for argc, which is
also not true, as i see 0 in my tests.

The following patch fixes up the test program to check for a NULL argv and also
touches the testcase itself to expect either 0 or 1 for argc depending on the
presence of argv, which is something we check early in the test.

This gives me full passes for aarch64-elf when running gdb.python/py-value.exp
and doesn't regress things on x86-64.

Ok?

gdb/testsuite/ChangeLog:

2016-10-06  Luis Machado  <lgustavo@codesourcery.com>

	* gdb.python/py-value.c (main): Check if argv is NULL before using it.
	* gdb.python/py-value.exp (test_value_in_inferior): Adjust initial
	argc value based on the existence of argv.
---
 gdb/testsuite/ChangeLog               |  6 ++++++
 gdb/testsuite/gdb.python/py-value.c   |  6 +++++-
 gdb/testsuite/gdb.python/py-value.exp | 13 +++++++++++--
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index d4ae9df..e1d689a 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2016-10-06  Luis Machado  <lgustavo@codesourcery.com>
+
+	* gdb.python/py-value.c (main): Check if argv is NULL before using it.
+	* gdb.python/py-value.exp (test_value_in_inferior): Adjust initial
+	argc value based on the existence of argv.
+
 2016-10-03  Antoine Tremblay  <antoine.tremblay@ericsson.com>
 2016-10-03  Simon Marchi  <simon.marchi@ericsson.com>
 
diff --git a/gdb/testsuite/gdb.python/py-value.c b/gdb/testsuite/gdb.python/py-value.c
index 586a0fd..8408e1e 100644
--- a/gdb/testsuite/gdb.python/py-value.c
+++ b/gdb/testsuite/gdb.python/py-value.c
@@ -82,7 +82,7 @@ char **save_argv;
 int
 main (int argc, char *argv[])
 {
-  char *cp = argv[0]; /* Prevent gcc from optimizing argv[] out.  */
+  char *cp;
   struct s s;
   union u u;
   PTR x = &s;
@@ -99,6 +99,10 @@ main (int argc, char *argv[])
   const char *sn = 0;
   struct str *xstr;
 
+  /* Prevent gcc from optimizing argv[] out.  */
+  if (argv != NULL)
+    cp = argv[0];
+
   s.a = 3;
   s.b = 5;
   u.a = 7;
diff --git a/gdb/testsuite/gdb.python/py-value.exp b/gdb/testsuite/gdb.python/py-value.exp
index 57a9ba1..bb802bf 100644
--- a/gdb/testsuite/gdb.python/py-value.exp
+++ b/gdb/testsuite/gdb.python/py-value.exp
@@ -274,10 +274,19 @@ proc test_value_in_inferior {} {
   gdb_test "python argc_notlazy.fetch_lazy()"
   gdb_test "python print (argc_lazy.is_lazy)" "True"
   gdb_test "python print (argc_notlazy.is_lazy)" "False"
-  gdb_test "print argc" " = 1" "sanity check argc"
+
+  # If argv is not available, then argc is likely not available as well, thus
+  # we expect it to be 0.
+  set argc_value 0
+  if { $has_argv0 } {
+    set argc_value 1
+  }
+
+  gdb_test "print argc" " = $argc_value" "sanity check argc"
+
   gdb_test "python print (argc_lazy.is_lazy)" "\r\nTrue"
   gdb_test_no_output "set argc=2"
-  gdb_test "python print (argc_notlazy)" "\r\n1"
+  gdb_test "python print (argc_notlazy)" "\r\n$argc_value"
   gdb_test "python print (argc_lazy)" "\r\n2"
   gdb_test "python print (argc_lazy.is_lazy)" "False"
 
-- 
2.7.4