[Vm-dev] Aarch64 number bug

[Bruce O'Neel]

Hi,

I have now gone back and checked this carefully.  The git repository
at the commit before this one produces the right answer for 2
raisedTo: 64 on Aarch64.  It produces the wrong answer, 0, when this
commit is included.

So it's this commit.  I'll look at the code to see if I can see why
the code is bad.

BTW, how would one find the two referenced packages?

cheers

bruce

On 2021-06-20T22:44:36.000+02:00, Bruce O'Neel
<bruce.oneel at pckswarms.ch> wrote:

> Playing with Git bisect gets us to the commit below as the first bad
> one.
> 
> I started the git bisect with the two commits below.  The first one
> is bad, the second is the good one.
> 
> a783502b249c4a4fedc88b6e07837d405feab144 - zero9 - builds, zero
> error.
> 
> 9f73148b8da4bc00278b83faa8da6b1c418fa54f - zero10 - builds works
> 
> Now this is not 100% guaranteed because one of the commits that git
> bisect chose had a build error so I had to mark that one as bad.
>  But the commit found does sound possible.
> 
> f632ee2888014ee88330ee994e13c9c609b57b5f is the first bad commit
> 
> commit f632ee2888014ee88330ee994e13c9c609b57b5f
> 
> Author: Eliot Miranda <eliot.miranda at gmail.com>
> 
> Date:   Wed Sep 2 10:45:27 2020 -0700
> 
>     CogVM source as per
> VMMaker.oscog-eem.2799/ClosedVMMaker-eem.98
> 
>     
> 
>     Ha!  I am *STUPID*.
> 
>     Integer overflow is not only determined by the upper 64-bits
> of a 64x64=>128 bit
> 
>     multiply being either all zero or all ones (0 or -1), but by
> the upper 64-bits
> 
>     being an extension of the most significant bit of the lower 64
> bits!!
> 
> :040000 040000 ffb8fbcd8ab5e2ca1936429b2daaade62909c178
> a5ac89d8b1d4980c5329835cdd3d4a2387b1fac5 M      nsspur64src
> 
> :040000 040000 e606dac14ee1db4ac59b0949bb03cd8e657d7aa7
> be666051cd1d52d0055e319432b66a0fba61063e M      spur64src
> 
> :040000 040000 1dea4faf99821c60e2c2461076bfe8b99d4dea9b
> afbef904e8cbc7e4b80e1606420dd6293e12f3e9 M      spurlowcode64src
> 
> :040000 040000 f66c681004806d5880af7c0a3115038f4f2f3361
> 0e8d76bedcf22b6ad7497ea2e3dc44f3c36c2f3a M      spursista64src
> 
> On 2021-06-20T21:48:49.000+02:00, Craig Latta
> <craig at blackpagedigital.com> wrote:
> 
>>  Hi Ken--
>>  
>>        I brought up a development environment on a Raspberry Pi 4.
>>  
>>   > Unfortunately, my attempt to build a VM simulator on aarch64 fails due
>>   > to a divide by zero bug.
>>   >
>>   > Perhaps because
>>   >    16r8000000000000000 printStringHex. ==> '0'
>>  
>>        update-eem-463.mcm has a postload action which turns on Sista, 
>>  which recompiles the system, which tries to recompile 
>>  FloatArrayTest>>testFloatArrayPluginPrimitiveAtPut, which exercises this 
>>  very bug during scanning, when trying to create the float 1e-127.
>>  
>>        For now I've rewritten testFloatArrayPluginPrimitiveAtPut and 
>>  testFloatArrayPluginPrimitiveAt on my system to do nothing. When 
>>  building GdbARMv8Plugin, there's some other kind of 
>>  header-include-ordering mayhem, similar to the problem with Linux 
>>  features.h when building the VM. (At least two levels of it, between 
>>  bfd.h and the aarch64 simulator's config.h, and config.h and other 
>>  system headers.) I expect no one has successfully built GdbARMv8Plugin 
>>  on anything but a M1 macOS machine so far.
>>  
>>  -C
>>  
>>  --
>>  Craig Latta  ::  research computer scientist
>>  Black Page Digital  ::  Berkeley, California
>>  663137D7940BF5C0AFC :: 1349FB2ADA32C4D5314CE

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