Re: [PATCH V5 2/2] Add mpx-bnd-init-on-return set/show command for inferior calls.

[Walfred Tedeschi <walfred.tedeschi@intel.com>]

Am 4/26/2016 um 5:19 PM schrieb Yao Qi:
> Walfred Tedeschi <walfred.tedeschi@intel.com> writes:
>
>> When using the return command, execution of a function is aborted
>> and present values are returned from that point.  That can cause
>> bound violations in the MPX context.  To avoid such side-effects,
>> a new setting ("mpx-bnd-init-on-return") was added to control
>> the initialization of bound register when using the return command.
>>
>
> We need to investigate why does "return" cause bound violations.  If the
> violations are caused by the invalid or garbage return value, that is
> expected, and it is a correct behavior to me.  If the return value is
> out of the bounds of registers settings, the violation is caused.  Can we
> tweak GDB to adjust the register settings to allow these memory accesses
> in the "return"?
>

Yao,

Thanks again for the prompt review! :)


The "return" causes a premature exit from the function. BND is only 
returning the bounds of the pointer which is returned in the usual way. 
  The novelty here is the BND registers. In case we are returning a 
pointer or address BND0 will carry the bounds of the pointer being 
returned. Once it is not set yet than garbage will be returned instead.

In this way the value is wrong and a bound violations is likely to happen.

Regards,
-Fred







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