> On Aug 30, 2018, at 9:02 PM, Jeff Law <[email protected]> wrote:
>
> On 08/30/2018 10:58 AM, Richard Henderson wrote:
>> On 08/28/2018 07:13 AM, Jeff Law wrote:
>>> Please consider using function descriptors rather than trampolines.
>>> This allows you to make the stack non-executable at all times which is
>>> good from a security standpoint. The downside is the indirect calling
>>> mechanism has to change slightly to distinguish between a simple
>>> indirect call and one through a function descriptor (usually by having a
>>> low bit on to indicate the latter). GIven this is an ABI change, now is
>>> probably the last opportunity to make this change.
>>
>> Correct me if I'm wrong here:
>>
>> Define TARGET_CUSTOM_FUNCTION_DESCRIPTORS to an appropriate value -- easy
>> for a
>> RISC target -- and that's it.
>>
>> Further, it pretty much only gets used by the Ada front end. One should not
>> expect these to be used by the C front end nested functions.
> I thought it was used more extensively than that... Thanks for checking
> into it though.
>
> Jeff
My impression from reading the internals manual is that it's an alternative to
trampolines -- and in fact it appears to suggest it's a superior alternative.
I've been planning to try turning it on for pdp11 where executable stacks can
be problematic. (For that matter, they are on lots of other machines -- which
is why descriptors instead of trampolines sounds like a good thing.)
paul
