Re: [PATCH v3] [gdb/testsuite] test a function call by hand from pretty printer

[Simon Marchi <simark@simark.ca>]

On 2022-03-14 16:39, Bruno Larsen via Gdb-patches wrote:
> The test case added here is testing the bug gdb/28856, where calling a
> function by hand from a pretty printer makes GDB crash. There are 6
> mechanisms to trigger this crash in the current test, using the commands
> backtrace, up, down, finish, step and continue. Since the failure happens
> because of use-after-free (more details below) the tests will always
> have a chance of passing through sheer luck, but anecdotally they seem
> to fail all of the time.
>
> The reason GDB is crashing is a use-after-free problem. The above
> mentioned functions save a pointer to the current frame's information,
> then calls the pretty printer, and uses the saved pointer for different
> reasons, depending on the function. The issue happens because
> call_function_by_hand needs to reset the obstack to get the current
> frame, invalidating the saved pointer.
> ---
>
> Changes from v2:
>     * Make .c follow GDB's coding style 2 - electric boogaloo
>     * .exp tests outputs, not just if GDB breaks or not
>     * added copyright header to .py file
>
> Changes from v1:
>     * make .c follow GDB's coding guidelines more closely
>     * Documented .exp file better
>     * renamed and refactored TCL proc to make it less confusing

Hi,

Having the test without the fix is annoying, because it crashes GDB on
an ASan-enabled build, and causes failures that did not exist before,
and the setup_kfails don't help for that.  This is something we
generally don't want, as we try to strictly progress towards less
failures.

Does the test actually test anything right now, given that everything is
broken?  If not, I'd suggest attaching the test case to the bug, and it
can be merged along with the fix.


Simon