[Larceny-users] SCE_BUFFER?

[Lars T Hansen]

Thanks.  ISTR that the 80386 needed a red zone to handle interrupts
and that that was fixed later, but it makes sense that signal handling
would still be using the user stack.  I don't know that I had ever
considered that.  Unices have a method of diverting the signal handler
to a separate stack (sigstack / sigaltstack), don't know if it's
entirely reliable or more widely available (eg Windows).

--lars

On Wed, Jul 11, 2012 at 5:22 PM, Felix S Klock II (Larceny-users list
proxy) <felixluser at pnkfx.org> wrote:
> Follow-up with relevant wiki links (roughly in order of supposed relevance):
>
>   https://trac.ccs.neu.edu/trac/larceny/wiki/ContIsEsp
>
>   https://trac.ccs.neu.edu/trac/larceny/wiki/SassyInvoke
>
>   https://trac.ccs.neu.edu/trac/larceny/wiki/IntelsOptimizationRules
>
>   https://trac.ccs.neu.edu/trac/larceny/wiki/IAssassinSetrtnInvoke
>
> Cheers,
> -Felix
>
> On Wed, Jul 11, 2012 at 11:08 AM, Felix S Klock II (Larceny-users list
> proxy) <felixluser at pnkfx.org> wrote:
>> Lars (cc'ing larceny-users)-
>>
>> If I recall correctly, Jesse Tov and I introduced the SCE_BUFFER to
>> support using the $esp register on Intel as the stack-cache pointer
>> (rather than the globals pointer, which I think was its role back when
>> you first developed the Petit/Nasm backend).
>>
>> The reason to use $esp as the stack-cache pointer is that it enables a
>> significantly faster call/return instruction sequence on Intel; see:
>>
>>   https://trac.ccs.neu.edu/trac/larceny/changeset/4000
>>
>> The reason we need a red-zone between the stack-cache and the nursery
>> is that you need some space above $esp in order to properly handle
>> interrupts or asynchronous signals or something along those lines.
>> (The notes on changeset:4000 don't actually 100% coincide with this
>> assertion, so I'm sure I'm getting the details wrong in this email.)
>>
>> The reason its only present on some realizations is that you only need
>> this red zone on Native Intel backends (Petit/Nasm and Sassy/IA32 aka
>> IAssassin), because that's the only place where $esp is being used in
>> this way.
>>
>> Cheers,
>> -Felix
>>
>> On Wed, Jul 11, 2012 at 10:10 AM, Lars T Hansen <lth at acm.org> wrote:
>>> Can somebody tell me why SCE_BUFFER (aka $sce.buffer), which appears
>>> to be some kind of red zone for the stack, was introduced into the
>>> runtime and why it was only done in some realizations?  Neither Sparc
>>> nor Standard-C make use of it.  I'm looking at code in a recent SVN
>>> checkout but I've not attempted to find out when it was introduced.
>>>
>>> --lars
>>>
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