Re: [gofrontend-dev] Re: [PATCH 00/13] Go closures, libffi, and the static chain

[Jay <jay.krell@cornell.edu>]

I worked on what I suspect is similar stuff.

I ran into the problem..pardon me if my terminology is wrong..PLT thunks for nested functions trashed registers that were in use. My solution was to mark them "hidden" or whatever is the term for not replaceable...also not exported but I recall not replaceable is more important.

 - Jay

On Nov 6, 2014, at 11:38 PM, Richard Henderson <rth@redhat.com> wrote:

> On 11/06/2014 06:45 PM, Ian Taylor wrote:
>> On Thu, Nov 6, 2014 at 5:04 AM, Richard Henderson <rth@redhat.com> wrote:
>>> 
>>> That said, this *may* not actually be a problem.  It's not the direct (possibly
>>> lazy bound) call into libffi that needs a static chain, it's the indirect call
>>> that libffi produces.  And the indirect calls that Go produces.
>>> 
>>> I'm pretty sure that there are no dynamically linked Go calls that require the
>>> static chain.  They're used for closures, which are either fully indirect from
>>> a different translation unit, or locally bound closures through which the
>>> optimizer has seen the construction, and optimized to a direct call.
>>> 
>>> Ian, have I missed a case where a closure could wind up with a direct call to a
>>> lazy bound function?
>> 
>> I think you've covered all the cases.  The closure value is only
>> required when calling a nested function.  There is no way to refer
>> directly to a nested function defined in a different shared library.
>> The only way you can get such a reference is if some function in that
>> shared library returns it.
> 
> Sorry, I wasn't clear.  I know nested functions must be local.
> 
> I'm asking about Go closures, supposing we go ahead with the change to
> make them use the static chain register.
> 
> I'm merely pretty sure that calling a closure is either fully indirect
> or local direct.
> 
> Certainly there are cases in the testsuite where -O3 is able to look
> through the creation of a closure and have a direct call to the function.
> 
> Given that closures are custom created for the data at the creation
> site, it seems unlikely that the optimizer could look through that and
> come up with a dynamically bound function.
> 
> 
> r~