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

Jan Vrany
2018-06-19T08:59:58Z

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