Re: [PATCH] fix bug with command `printf "%s\n", $_as_string($pc)`

[Matthew Malcomson <hardenedapple at gmail dot com>]

On 20/02/17 18:19, Simon Marchi wrote:
> On 2017-02-19 12:32, Matthew Malcomson wrote:
> > diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
> > index eb3d307b19..c786f68865 100644
> > --- a/gdb/python/py-value.c
> > +++ b/gdb/python/py-value.c
> > @@ -1615,7 +1615,7 @@ convert_value_from_python (PyObject *obj)
> >        gdb::unique_xmalloc_ptr<char> s
> >          = python_string_to_target_string (obj);
> >        if (s != NULL)
> > -        value = value_cstring (s.get (), strlen (s.get ()),
> > +        value = value_cstring (s.get (), strlen (s.get ()) + 1,
> >                     builtin_type_pychar);
> >      }
> >        else if (PyObject_TypeCheck (obj, &value_object_type))
>
> This fix looks good to me.
>
> One test (py-mi.exp) needs to be updated though.  You can run all the 
> Python-related tests using:
>
>   $ make check TESTS="gdb.python/*.exp"
>
> Normally, the Python tests all pass reliably, unlike some other parts 
> of the testsuite.
>
> It might also be good to improve gdb.python/py-as-string.exp to 
> include a test for this bug.
>
> Thanks,
>
> Simon

Thanks -- I had mistakenly ignored the py-mi.exp failure assuming it was 
nothing to do with me (my apologies).

I've included the test fixes you suggested below.

------------------------------------------------

CHANGELOG:

2017-02-19  Matthew Malcomson <hardenedapple@gmail.com>

    * python/py-value.c (convert_value_from_python): Include NULL 
terminator in result.
    testsuite/gdb.python/py-as-string.c, 
testsuite/gdb.python/py-as-string.exp: Update tests
    to account for NULL terminator from python string values.
    doc/gdb.texinfo ($trace_func): Mention this value can't be used 
with printf.

-------------------------------------------------

PATCH:


commit 44fd8bd7af5cf4c6b32846dd78ebfecb7b8d9fa5
Author: Matthew Malcomson <hardenedapple@gmail.com>
Date:   Sun Feb 19 14:35:09 2017 +0000

    convert_value_from_python include terminating NULL

    When converting python strings to internal gdb Value strings, the NULL
    byte was initially left out, this can result in extra data from the
    inferior being printed when the resulting value is used with
    printf "%s\n", value

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index c465dc2f9f..5fb34853f1 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -13645,8 +13645,8 @@ The source file for the current trace snapshot.
 The name of the function containing @code{$tracepoint}.
 @end table

-Note: @code{$trace_file} is not suitable for use in @code{printf},
-use @code{output} instead.
+Note: @code{$trace_file} and @code{$trace_file} are not suitable for use in
+@code{printf}, use @code{output} instead.

 Here's a simple example of using these convenience variables for
 stepping through all the trace snapshots and printing some of their
diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
index eb3d307b19..c786f68865 100644
--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -1615,7 +1615,7 @@ convert_value_from_python (PyObject *obj)
       gdb::unique_xmalloc_ptr<char> s
         = python_string_to_target_string (obj);
       if (s != NULL)
-        value = value_cstring (s.get (), strlen (s.get ()),
+        value = value_cstring (s.get (), strlen (s.get ()) + 1,
                    builtin_type_pychar);
     }
       else if (PyObject_TypeCheck (obj, &value_object_type))
diff --git a/gdb/testsuite/gdb.python/py-as-string.c 
b/gdb/testsuite/gdb.python/py-as-string.c
index de2e8a1951..c35a692712 100644
--- a/gdb/testsuite/gdb.python/py-as-string.c
+++ b/gdb/testsuite/gdb.python/py-as-string.c
@@ -15,6 +15,8 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see 
<http://www.gnu.org/licenses/>. */

+#include <stddef.h>
+
 enum EnumType {
   ENUM_VALUE_A,
   ENUM_VALUE_B,
@@ -22,6 +24,19 @@ enum EnumType {
   ENUM_VALUE_D,
 };

+static char arena[51] = 
"xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
+
+/* Override malloc() so value_coerce_to_target() gets a known pointer, 
and we
+   know we'll see an error if $_as_string() returns a string that isn't 
NULL
+   terminated. */
+void *malloc(size_t size)
+{
+    if (size > sizeof(arena))
+        return NULL;
+
+    return arena;
+}
+
 static enum EnumType enum_valid = ENUM_VALUE_B;
 static enum EnumType enum_invalid = 20;

diff --git a/gdb/testsuite/gdb.python/py-as-string.exp 
b/gdb/testsuite/gdb.python/py-as-string.exp
index 0c44d5f174..819442834c 100644
--- a/gdb/testsuite/gdb.python/py-as-string.exp
+++ b/gdb/testsuite/gdb.python/py-as-string.exp
@@ -35,6 +35,12 @@ proc test_as_string { } {
     gdb_test "p \$_as_string(2)" "\"2\""
     gdb_test "p \$_as_string(enum_valid)" "\"ENUM_VALUE_B\""
     gdb_test "p \$_as_string(enum_invalid)" "\"20\""
+    # Test that the NULL character is included in the returned value.
+    gdb_test "printf \"%s\\n\", \$_as_string(\"hi\")" "\"hi\""
+    # Quote once to define the string, and once for the regexp.
+    gdb_test "interpreter-exec mi '-var-create test * 
\$_as_string(\"Hello\")'" \
+ "\\^done,name=\"test\",numchild=\"8\",value=\"\\\[8]\",type=\"char 
\\\[8]\",has_more=\"0\""
+    gdb_test "interpreter-exec mi '-var-delete test'" 
"\\^done,ndeleted=\"1\""
 }

 test_as_string
diff --git a/gdb/testsuite/gdb.python/py-mi.exp 
b/gdb/testsuite/gdb.python/py-mi.exp
index 736dc7a0d6..a5ad3f0f44 100644
--- a/gdb/testsuite/gdb.python/py-mi.exp
+++ b/gdb/testsuite/gdb.python/py-mi.exp
@@ -281,7 +281,7 @@ mi_create_dynamic_varobj nstype2 nstype2 1 \
   "create nstype2 varobj"

 mi_list_varobj_children nstype2 {
-    { {nstype2.<error at 0>} {<error at 0>} 6 {char \[6\]} }
+    { {nstype2.<error at 0>} {<error at 0>} 7 {char \[7\]} }
 } "list children after setting exception flag"

 mi_create_varobj me me \