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

[Jan Vrany <jan dot vrany at fit dot cvut dot cz>]

On Mon, 2018-06-18 at 20:42 -0400, Simon Marchi wrote:
> On 2018-06-04 09:15 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 to MI consumer as described
> > in
> > the documentation.
> 
> Hi Jan,
> 
> Thanks for the patch.  I think we should also handle the indirect
> children
> of dynamic objects.  When trying this test program:
> 
> #include <vector>
> struct foo { int a; };
> int main() {
>     std::vector<foo> vec;
>     vec.push_back({ 1 });
>     return 0;
> }
> 
> With the following MI commands:
> 
> -enable-pretty-printing
> b 6
> r
> -var-create - * vec
> -var-list-children var1
> -var-list-children var1.[0]
> -var-list-children var1.[0].public
> -var-info-path-expression var1.[0].public.a
> 
> I get this:
> 
> ~"/home/simark/src/binutils-gdb/gdb/varobj.c:969: internal-error:
> const char* varobj_get_path_expr(const varobj*): Assertion
> `!varobj_is_dynamic_p(var->parent)' failed..."
> 
Hi Simon, 

good catch! Will fix that. 


> I noted some small formatting nits below.

Thanks! I appreciate the patience you have with me.
I will address your
comments and send new version.

Best, Jan

> 
> > gdb/ChangeLog:
> > 
> > 	* mi/mi-cmd-var.c: Report an error if varobj is a child of
> > dynamic
> > 	varobj as stated in documentation.
> > 	* varobj.c: New assert.
> > 
> > gdb/testsuite/Changelog:
> > 
> > 	* gdb.pythonpy-mi-var-info-path-expression.c: New file.
> 
> You are missing a slash here (and in the ChangeLog file itself).
> 
> > 	* gdb.python/py-mi-var-info-path-expression.py: New file.
> > 	* gdb.python/py-mi-var-info-path-expression.exp: New file.
> > ---
> >  gdb/ChangeLog                                 |  6 ++
> >  gdb/mi/mi-cmd-var.c                           |  5 ++
> >  gdb/testsuite/ChangeLog                       |  6 ++
> >  .../py-mi-var-info-path-expression.c          | 40 ++++++++++
> >  .../py-mi-var-info-path-expression.exp        | 77
> > +++++++++++++++++++
> >  .../py-mi-var-info-path-expression.py         | 45 +++++++++++
> >  gdb/varobj.c                                  |  6 +-
> >  7 files changed, 184 insertions(+), 1 deletion(-)
> >  create mode 100644 gdb/testsuite/gdb.python/py-mi-var-info-path-
> > expression.c
> >  create mode 100644 gdb/testsuite/gdb.python/py-mi-var-info-path-
> > expression.exp
> >  create mode 100644 gdb/testsuite/gdb.python/py-mi-var-info-path-
> > expression.py
> > 
> > diff --git a/gdb/ChangeLog b/gdb/ChangeLog
> > index a292f4c056..fc5edb9a9e 100644
> > --- a/gdb/ChangeLog
> > +++ b/gdb/ChangeLog
> > @@ -1,3 +1,9 @@
> > +2018-06-04  Jan Vrany  <jan.vrany@fit.cvut.cz>
> > +
> > +	* mi/mi-cmd-var.c: Report an error if varobj is a child of
> > dynamic
> > +	varobj as stated in documentation.
> > +	* varobj.c: New assert.
> > +
> >  2018-06-04  Pedro Alves  <palves@redhat.com>
> >  
> >  	* darwin-nat.c (darwin_ops): Delete.
> > diff --git a/gdb/mi/mi-cmd-var.c b/gdb/mi/mi-cmd-var.c
> > index 38c59c7e66..f278281023 100644
> > --- a/gdb/mi/mi-cmd-var.c
> > +++ b/gdb/mi/mi-cmd-var.c
> > @@ -438,6 +438,11 @@ mi_cmd_var_info_path_expression (const char
> > *command, char **argv, int argc)
> >  
> >    /* Get varobj handle, if a valid var obj name was specified.  */
> >    var = varobj_get_handle (argv[0]);
> > +
> > +  /* -var-info-path-expression is currently not valid for children
> > of
> > +     a dynamic varobj  */
> 
> Finish the sentence with a period.
> 
> > diff --git a/gdb/varobj.c b/gdb/varobj.c
> > index a0df485ae9..87bfd44549 100644
> > --- a/gdb/varobj.c
> > +++ b/gdb/varobj.c
> > @@ -962,9 +962,13 @@ varobj_get_path_expr (const struct varobj
> > *var)
> >        /* For root varobjs, we initialize path_expr
> >  	 when creating varobj, so here it should be
> >  	 child varobj.  */
> > -      struct varobj *mutable_var = (struct varobj *) var;
> >        gdb_assert (!is_root_p (var));
> >  
> > +      /* Computation of full rooted expression for children of
> > dynamic
> > +         varobjs is not supported. */
> 
> Two spaces after the final period (before the */).
> 
> > +      gdb_assert (!varobj_is_dynamic_p(var->parent));
> 
> Space after varobj_is_dynamic_p.
> 
> Thanks,
> 
> Simon