[Vm-dev] Aarch64 number bug
Bruce O'Neel
bruce.oneel at pckswarms.ch
Sun Jun 20 20:44:36 UTC 2021
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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