Re: [9fans] assembly syntax in plan 9

[Comeau At9Fans <comeauat9fans@gmail.com>]

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On Wed, Jan 18, 2012 at 12:48 PM, Bakul Shah <bakul@bitblocks.com> wrote:

> On Jan 17, 2012, at 11:21 AM, Comeau At9Fans <comeauat9fans@gmail.com>
> wrote:
> On Mon, Jan 16, 2012 at 2:03 PM, Bakul Shah <bakul@bitblocks.com> wrote:
>
> How do you deal with longjmp?
>>
>
> I don't have it in front of me, but I do seem to recall the Standard
> allows that the VLA might still be around though, believe it has an example
> with said, for better or worse...
>
>
> Do you have a reference?
>

Ok, so, gunna make me look, let's see, ok: 7.13.2.1p5, note the may's and
might's.  There should be narrative backing those up.


> On Jan 16, 2012, at 10:51 AM, Comeau At9Fans <comeauat9fans@gmail.com>
>> wrote:
>>
>> On Mon, Jan 16, 2012 at 10:41 AM, Bakul Shah <bakul@bitblocks.com> wrote:
>>
>>> A frame pointer is needed for C99's variable length arrays but not
>>> otherwise. Only an issue if ever plan9 C is extended to handle C99 or C1x.
>>> gcc has to do the right thing even with -fno-frame-pointer.
>>>
>>
>> What we do in problematic cases with Comeau is to generate code to
>> arrange for the allocation of the VLA on the heap.  I'm not saying this is
>> perfect, but at least it gets the feature implementable and up and running
>> as "a portable implementation" versus perhaps not being able to implement
>> it at all on some platforms.
>>
>>
> Seems to me if you can port C, you can use a FP to implement VLAs without
> alloca games and more efficiently. You can always store the FP in stack
> local memory if out of registers.
>

I probably overstated the situation by saying not being able to implement
it at all... probably should have said I never thought of it beyond the
obvious implementations.

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