[PING][PATCH] [gdb/python] Make gdb.UnwindInfo.add_saved_register more robust

[Tom de Vries <tdevries@suse.de>]

On 3/2/24 13:36, Tom de Vries wrote:
> On arm-linux, until commit bbb12eb9c84 ("gdb/arm: Remove tpidruro register
> from non-FreeBSD target descriptions") I ran into:
> ...
> FAIL: gdb.base/inline-frame-cycle-unwind.exp: cycle at level 5: \
>    backtrace when the unwind is broken at frame 5
> ...
> 
> What happens is the following:
> - the TestUnwinder from inline-frame-cycle-unwind.py calls
>    gdb.UnwindInfo.add_saved_register with reg == tpidruro and value
>    "<unavailable>",
> - pyuw_sniffer calls value->contents ().data () to access the value of the
>    register, which throws an UNAVAILABLE_ERROR,
> - this causes the TestUnwinder unwinder to fail, after which another unwinder
>    succeeds and returns the correct frame, and
> - the test-case fails because it's counting on the TestUnwinder to succeed and
>    return an incorrect frame.
> 
> Fix this by checking for !value::entirely_available as well as
> valued::optimized_out in unwind_infopy_add_saved_register.
> 
> Tested on x86_64-linux and arm-linux.
> 

Ping.

Thanks,
- Tom

> PR python/31437
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31437
> ---
>   gdb/python/py-unwind.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
> 
> diff --git a/gdb/python/py-unwind.c b/gdb/python/py-unwind.c
> index 56f925bc57f..1c1289f7e7d 100644
> --- a/gdb/python/py-unwind.c
> +++ b/gdb/python/py-unwind.c
> @@ -362,6 +362,18 @@ unwind_infopy_add_saved_register (PyObject *self, PyObject *args, PyObject *kw)
>         return nullptr;
>       }
>   
> +  if (value->optimized_out () || !value->entirely_available ())
> +    {
> +      /* If we allow this value to be registered here, pyuw_sniffer is going
> +	 to run into an exception when trying to access its contents.
> +	 Throwing an exception here just puts a burden on the user to
> +	 implement the same checks on the user side.  We could return False
> +	 here and True otherwise, but again that might require changes in user
> +	 code.  So, handle this with minimal impact for the user, while
> +	 improving robustness: silently ignore the register/value pair.  */
> +      Py_RETURN_NONE;
> +    }
> +
>     gdbpy_ref<> new_value = gdbpy_ref<>::new_reference (pyo_reg_value);
>     bool found = false;
>     for (saved_reg &reg : *unwind_info->saved_regs)
> 
> base-commit: a6a3b67fa9052bba81ed91a38569c11ecb95baf1