[PATCH v3] Fix segfault when invoking -var-info-path-expression on a dynamic varobj

[Jan Vrany]

On Thu, 2018-06-28 at 12:03 -0400, Simon Marchi wrote:
> On 2018-06-28 11:17 AM, Jan Vrany wrote:
> > Invoking -var-info-path-expression on a dynamic varobj lead either
> > in wrong
> > (nonsense) result or to a segmentation fault in
> > cplus_describe_child().
> > This was caused by the fact that varobj_get_path_expr() called
> > cplus_path_expr_of_child() ignoring the fact the parent of the
> > variable
> > is dynamic. Then, cplus_describe_child() accessed the underlaying C
> > type
> > members by index, causing (i) either wrong (nonsense) expression
> > being
> > returned (since dynamic child may be completely arbibtrary value)
> > or (ii) segmentation fault (in case the index higher than number of
> > underlaying C type members.
> > 
> > This fixes the problem by checking whether a varobj is a child of a
> > dynamic
> > varobj and, if so, reporting an error as described in
> > documentation.
> 
> Hi Jan,
> 
> Thanks, this builds fine now.  The test doesn't pass here
> though.  Does it
> pass on your side?

Hi Simon, 

yes, it passes on my machine. 

> 
> $ make check TESTS="gdb.python/py-mi-var-info-path-expression.exp"
> ...
> FAIL: gdb.python/py-mi-var-info-path-expression.exp: -var-create c1 *
> &c1 (unexpected output)
> FAIL: gdb.python/py-mi-var-info-path-expression.exp: -var-list-
> children c1 (unexpected output)
> FAIL: gdb.python/py-mi-var-info-path-expression.exp: -var-list-
> children c1.cdr (unexpected output)
> FAIL: gdb.python/py-mi-var-info-path-expression.exp: -var-list-
> children c1.car (unexpected output)
> FAIL: gdb.python/py-mi-var-info-path-expression.exp: -var-list-
> children c1.car.atom (unexpected output)
> 
> I'm seeing some Python exception in testsuite/gdb.log, I didn't dig
> more than that:
> 
> -var-create c1 * &c1
> 
> &"Traceback (most recent call last):\n"
> 
> &"  File \"/home/emaisin/src/binutils-
> gdb/gdb/testsuite/gdb.python/py-mi-var-info-path-expression.py\",
> line 24, in to_string\n"
> 
> &"    if int(self._val) == 0:\n"
> 
> &"gdb.error: Cannot convert value to int.\n"

Uff, I think I know what's the problem, Python 3.x vs Python 2.x.
My GDB is compiled with 3.x and - I guess - yours is with Python 2.x. 

I'll fix the python code to work on both later today. Sorry about it. 

Jan