[Vm-dev] Re: vm problem on cog an stack v3

[Nicolas Cellier]

To be more specific,

The first thing to do would be to confirm that the KernelNumber tests fail
with a squeak.stack.v3 VM compiled with head revision of COG VM branch,
whatever OS.

Then knowing from which SVN version of COG VM branch the KernelNumber the
tests start failing would be nice.

The bisect job is to:
- iterate on version number (whatever strategy, bsearch or something)
- checkout VM sources
- compile the build.favouriteOS/squeak.stack.v3
- run a v3 image with the generated VM and launch KernelNumber tests

Really a job for a jenkins bot, travis bot or whatever...
The next good thing would be to give a little love to build.squeak.org or
anyother similar solution.
I only see red disks on this site...

2016-03-27 0:40 GMT+01:00 Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com>:

> Hi,
> before I continue, i've noticed that the large integer multiply seems
> broken on v3 object memory (cog & stack)
> Note that this does not happen on Spur.
>
> This is independent of my recent changes of LargeIntegers plugin as it
> happens BEFORE these changes and is related to primitive 29 rather than to
> the plugin...
> Here are the symptoms:
>
> halfPower := 10000.
> s := 111111111111111.
> head := s quo: halfPower.
> tail := s - (head * halfPower).
> {
>    head as: ByteArray.
>    (1 to: halfPower digitLength) collect: [:i | halfPower digitAt: i] as:
> ByteArray.
>    (head*halfPower) as: ByteArray.
> }.
>
> the correct result is:
>  #(#[199 25 70 150 2] #[16 39] #[112 237 78 18 14 101])
>
> the wrong result I obtained with SVN revision 3651 compiled by myself is:
>  #(#[199 25 70 150 2] #[16 39] #[112 237 78 18 254 61])
>
> The most significant bits (above 32) are wrong...
> The pattern I obtain is (with most significant bit put back left)
>
> 2r00111101 << 8 +  2r11111110   "wrong result"
> 2r01100101 << 8 + 2r00001110  "Correct result"
>
> I completely fail to infer what's going on from this pattern...
>
> This is on MacOSX clang --version
> Apple LLVM version 7.3.0 (clang-703.0.29)
> Target: x86_64-apple-darwin15.4.0
>
> This goes thru primitiveMultiplyLargeIntegers (29)
> oopResult := self magnitude64BitIntegerFor: result neg: aIsNegative ~=
> bIsNegative.
> -> sz > 4
>                 ifTrue: [objectMemory storeLong64: 0 ofObject:
> newLargeInteger withValue: magnitude]
> (which I changed recently)
>
> then:
> storeLong64: longIndex ofObject: oop withValue: value
>     <var: #value type: #sqLong>
>     self flag: #endianness.
>     self long32At: oop + self baseHeaderSize + (longIndex << 3) put: (self
> cCode: [value] inSmalltalk: [value bitAnd: 16rFFFFFFFF]);
>         long32At: oop + self baseHeaderSize + (longIndex << 3) + 4 put:
> (value >> 32).
>     ^value
>
> I don't see anything wrong with this code...
> Well, using a shift on signed value is not that good, but it works for at
> least 3 reasons:
> - we throw the signBit extension away
> - slang inlining misses the signedness difference, and the generated C
> code is correct.
> - Anyway, in our case, the sign bit was 0...
>
> Previous implementation in magnitude64BitIntegerFor:neg: was:
> sz > 4 ifTrue:
>                 [objectMemory storeLong32: 1 ofObject: newLargeInteger
> withValue: magnitude >> 32].
>             objectMemory
>                 storeLong32: 0
>                 ofObject: newLargeInteger
>                 withValue: (self cCode: [magnitude] inSmalltalk:
> [magnitude bitAnd: 16rFFFFFFFF])
>
> Not much different, except that the high 32 bits and low 32 bits are
> written in a different order...
>
> If I had a server I'd like to bisect
> - from which version does this happens
> - for which OS
> - for which compiler
>
> Without such information, I think I'll have to debug it either thru
> simulator or directly in gdb, but I feel like I'm really losing my time :(
>
> And I've got a 2nd problem like this one...
>
>
>
>
>
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