[Vm-dev] Aarch64 number bug

[Craig Latta]

Hi Ken--

      I built GdbARMv8Plugin on macOS without a hitch, but it failed 
primitively before doing any actual work, during startup.

      Before that I tried to build in Linux on a Raspberry Pi, but there 
was multi-level header-ordering hell even worse that the one involving 
Linux features.h and our sq.h. When I got to the point of two Linux 
headers both saying they should be included before the other, I stopped.

      I do think, though, that Tobias' theory is compelling:

      On 21/6/21 04:20, Tobias Pape wrote:

 > Hi
 >
 >
 >> On 21. Jun 2021, at 12:15, Bruce O'Neel <bruce.oneel at pckswarms.ch> 
wrote:
 >>
 >> 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?
 >
 > https://source.squeak.org/VMMaker/ has all the packages. (or 
http://source.squeak.org/VMMaker.html)
 >
 > 	The diff for the first one 
(https://source.squeak.org/VMMaker/VMMaker.oscog-eem.2799.diff) ist 
truncated,
 > 	while the diff-changeset is ok: 
http://source.squeak.org/VMMaker/changes/VMMaker.oscog-eem.2799(2798).cs
 > 	(you see all changed methods, but not the actual diff)
 >
 > But this only adds the JumpMulOverflow / JumpNoMulOverflow 
names/class-vars.
 >
 > The implementation diff is found at
 > 	http://www.squeaksource.com/ClosedVMMaker/ClosedVMMaker-eem.98.diff
 >
 > I would suggest that our bug does not concern Jumps, but rather only 
Mul, so we have to start looking
 > at the differences for concretizeMulOverflowRRR ...
 >
 >  From what I see, tho, is that the MUL and the SMULH instruction 
order has been reversed.
 >
 > (Also, the arm blog uses an different interesting method of detecting 
overflow,
 > by missusing the argument shitfter of CMP: 
https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/detecting-overflow-from-mul
 > Although this is written for older arm, it seems to be applicable to 
the 64-variant too)
 >
 > Best regards
 > 	-Tobias


-C

***

      On 26/6/21 15:43, ken.dickey at whidbey.com wrote:

 > Small progress.
 >
 > The stack interpreter and cog VMs share the LargeIntegers plugin, but
 >    stack:
 > (16r8000000000000000 * 16) printStringHex."--> '80000000000000000' "
 >    cog:
 > (16r8000000000000000 * 16) printStringHex." --> '0' "
 >
 > I was able to build a SpurVMMaker.image using the stack-interpreter VM
 > and would like to invoke:
 >    StackToRegisterMappingCogit
 >      genAndDis: Integer class>>#xReadFrom:base:
 >
 > But have had zero success in building the required GdbARMv8Plugin
 > [Linux/aarch64].
 >
 > Can some kind soul who actually knows how to deal with the fragile and
 > complex C environment help me out?
 >
 > Thanks much,
 > -KenD

--
Craig Latta  ::  research computer scientist
Black Page Digital  ::  Berkeley, California
663137D7940BF5C0AFC :: 1349FB2ADA32C4D5314CE