[Vm-dev] Re: Spur 64-bits. Ugh, this could be a slog...
eliot.miranda at gmail.com
Wed Nov 19 18:19:34 UTC 2014
On Tue, Nov 18, 2014 at 7:59 PM, Ryan Macnak <rmacnak at gmail.com> wrote:
> What about bytecode pc's? These are indexed based on the physical size of
> the literals. I don't like the idea of debugging pc -> source mappings, pc
> coverage data, etc needing invalidation after starting an image on a
> platform with a different word size.
I think this is taken care of. For example, CompiledMethod>>initialPC
already consults wordSize.
"Answer the program counter for the receiver's first bytecode."
^ (self numLiterals + 1) * Smalltalk wordSize + 1
and of course the image bootstrap maps pcs already. i.e.
Spur32to64BitBootstrap>>fillInPointerObjectWithPC: obj64 from: obj32
| method |
self fillInPointerObject: obj64 from: obj32.
(heap64 classIndexOf: obj64) = ClassBlockClosureCompactIndex ifTrue:
[method := heap32
self incrementPCField: ClosureStartPCIndex ofObject: obj64 for: method].
(heap64 classIndexOf: obj64) = ClassMethodContextCompactIndex ifTrue:
[method := heap32
self incrementPCField: InstructionPointerIndex ofObject: obj64 for: method]
Spur32to64BitBootstrap>>incrementPCField: fieldIndex ofObject: obj64 for:
| value nLits |
value := heap64 fetchPointer: fieldIndex ofObject: obj64.
(heap64 isIntegerObject: value)
[nLits := heap32 literalCountOf: method32.
withValue: (heap64 integerObjectOf: nLits + LiteralStart * 4 + (heap64
[self assert: (reverseMap at: value) = heap32 nilObject]
So I'm more looking for issues where the code implicitly assumes 32-bit
pointers, such as digitAt: below.
On Tue, Nov 18, 2014 at 7:12 PM, Eliot Miranda <eliot.miranda at gmail.com>
>> Hi All,
>> I'm making good progress on 64-bit Spur in the Stack VM simulator.
>> But I've just noticed an image-level issue which could be indicative of
>> lots of 32-bit assumptions baked into the Squeal/Pharo/Newspeak systems.
>> SmallInteger>>digitAt: n
>> "Answer the value of an indexable field in the receiver.
>> LargePositiveInteger uses bytes of base two number, and each is a 'digit'
>> base 256. Fail if the argument (the index) is not an Integer or is out of
>> n>4 ifTrue: [^ 0].
>> self < 0
>> [self = SmallInteger minVal ifTrue:
>> ["Can't negate minVal -- treat specially"
>> ^ #(0 0 0 64) at: n].
>> ^ ((0-self) bitShift: (1-n)*8) bitAnd: 16rFF]
>> ifFalse: [^ (self bitShift: (1-n)*8) bitAnd: 16rFF]
>> This assumes that SmallInteger is only ever 4 bytes, which is
>> unacceptably wasteful for my approach to 64-bits. In 64-bit Spur,
>> SmallIntegers are 61-bit 2's complement.
>> I'm raising this example at this point to see if the community might find
>> similar issues and bring them to my attention.
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