[PATCH V1] Fix of default lookup for "this" symbol.

[Walfred Tedeschi <walfred.tedeschi@intel.com>]

Using the default lookup for the symbol "this" might lead to segmentation
fault in GDB.
Some languages, e.g. Fortran, use as default lookup routine the C++
routines.
For those languages "this" can be the instance of a class or even the
definition of a class.
When an instance of a class having the name "this" is evaluated
in GDB a segmentation fault was observed.

As example of the issue take into consideration the Fortran code:
  type foo
    real :: a
    type(bar) :: x
    character*7 :: b
  end type foo
  type(foo) :: this

Issue appears when evaluating the variable "this" in GDB.

Within the language definition structure there is a field that represents
the name of the special symbol used for the C++ "this" for the language
being described.
The fix presented here takes into account the aforementioned field. In the
case the aforementioned field is NULL "this" is not represented in the
language described and the lookup should return a null_block_symbol.

Tests: Performed tests with gfortran and ifort.

2016-03-09  Walfred Tedeschi  <walfred.tedeschi@intel.com>

gdb/ChangeLog:

	* cp_lookup_bare_symbol (cp_lookup_bare_symbol): Add check for the
	name_of_this in order to return a null symbol when looking up
	for "this".

gdb/testsuite/ChangeLog:

	* gdb.fortran/derived-types.exp (result_line, result_line_2):
	New variables.
	(print this%a, print this%b, print this): New tests.
	* gdb.fortran/derived-types.f90 (this): New object and
	initialization.

---
 gdb/cp-namespace.c                         |  7 ++++++
 gdb/testsuite/gdb.fortran/derived-type.exp | 35 ++++++++++++++++++++++++++++--
 gdb/testsuite/gdb.fortran/derived-type.f90 |  7 +++++-
 3 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/gdb/cp-namespace.c b/gdb/cp-namespace.c
index 016a42f..7eb3a13 100644
--- a/gdb/cp-namespace.c
+++ b/gdb/cp-namespace.c
@@ -210,6 +210,13 @@ cp_lookup_bare_symbol (const struct language_defn *langdef,
       if (lang_this.symbol == NULL)
 	return null_block_symbol;
 
+      /* This whole routine is also the default path for several languages.
+         In some languages "this" is not a special symbol,
+         i.e. LA_NAME_OF_THIS is NULL.
+         For those cases we should return a null_block_symbol.  */
+      if (langdef != NULL && langdef->la_name_of_this == NULL)
+	return null_block_symbol;
+
       type = check_typedef (TYPE_TARGET_TYPE (SYMBOL_TYPE (lang_this.symbol)));
       /* If TYPE_NAME is NULL, abandon trying to find this symbol.
 	 This can happen for lambda functions compiled with clang++,
diff --git a/gdb/testsuite/gdb.fortran/derived-type.exp b/gdb/testsuite/gdb.fortran/derived-type.exp
index 32431bc..2781850 100644
--- a/gdb/testsuite/gdb.fortran/derived-type.exp
+++ b/gdb/testsuite/gdb.fortran/derived-type.exp
@@ -73,14 +73,45 @@ gdb_test_multiple $test $test {
 gdb_test "print q%x%c" "\\$\[0-9\]+ = 1"
 gdb_test "print q%x%d" "\\$\[0-9\]+ = 2\\.375"
 
+set result_line "= \\( a = 3.125, x = \\( c = 1, d = 2\\.375 \\),\
+b = 'abcdefg' \\)\r\n$gdb_prompt $"
+
+# Used in case compiler generates an array of characters.
+set result_line_2 " = \\( a = 3.125, x = \\( 1, 2\\.375 \\),\
+b = \\('abcdefg'\\) \\)\r\n$gdb_prompt $"
+
 set test "print q"
 gdb_test_multiple $test $test {
-    -re "\\$\[0-9\]+ = \\( a = 3.125, x = \\( c = 1, d = 2\\.375 \\), b = 'abcdefg' \\)\r\n$gdb_prompt $" {
+    -re $result_line {
 	pass $test
     }
-    -re "\\$\[0-9\]+ = \\( a = 3.125, x = \\( 1, 2\\.375 \\), b = \\('abcdefg'\\) \\)\r\n$gdb_prompt $" {
+    -re $result_line_2 {
 	# Compiler should produce string, not an array of characters.
 	setup_xfail "*-*-*"
 	fail $test
     }
 }
+
+gdb_test "print this%a" " = 3\\.125"
+
+set test "print this%b"
+gdb_test_multiple $test $test {
+    -re " = 'abcdefg'\r\n$gdb_prompt $" {
+        pass $test
+    }
+    -re $result_line_2 {
+        setup_xfail "*-*-*"
+        fail $test
+    }
+}
+
+set test "print this"
+gdb_test_multiple $test $test {
+    -re $result_line {
+        pass $test
+    }
+    -re $result_line_2 {
+         setup_xfail "*-*-*"
+         fail $test
+    }
+}
diff --git a/gdb/testsuite/gdb.fortran/derived-type.f90 b/gdb/testsuite/gdb.fortran/derived-type.f90
index 2cb2339..aad1553 100644
--- a/gdb/testsuite/gdb.fortran/derived-type.f90
+++ b/gdb/testsuite/gdb.fortran/derived-type.f90
@@ -29,12 +29,17 @@ program main
   end type foo
   type(foo) :: q
   type(bar) :: p
+  type(foo) :: this
 
   p = bar(1, 2.375)
   q%a = 3.125
   q%b = "abcdefg"
   q%x%c = 1
   q%x%d = 2.375
-  print *,p,q 
+  this%a = 3.125
+  this%b = "abcdefg"
+  this%x%c = 1
+  this%x%d = 2.375
+  print *,p,q,this
 
 end program main
-- 
2.7.4