[libre-riscv-dev] spike-sv non-default element widths

[Jacob Lifshay]

On Thu, Oct 11, 2018 at 1:49 AM lkcl <lkcl at libre-riscv.org> wrote:

> all of those never produce the word "FAILED" for all x in range 0-255
> for all y in range 0-255 for all operands plus, minus, mul, div,
> remainder (modulo), shiftleft and shiftright.
>

In
https://git.libre-riscv.org/?p=riscv-isa-sim.git;a=blob;f=operators/operators.t.cc;h=b5ac0185adba82ad8424401a50807f63ecb383ea;hb=c3d43aa1e221c74936adac7673f1923cbec5fdd0
You definitely need to check the assembly output as the first time it hits
the divide op it has a divide by zero (y == 0), so the compiler could be
optimizing everything out assuming it's unreachable. Try compiling with
"-fsanitize=undefined", that should tell you when you do something that the
compiler assumes doesn't happen.

>  can you see anything wrong with the test code, that it might be
> producing the wrong answers at line 19?
>
Divide by zero among other things. Also, j is not initialized to anything.

>
>
> https://git.libre-riscv.org/?p=riscv-isa-sim.git;a=blob;f=operators/operators.t.cc;h=b5ac0185adba82ad8424401a50807f63ecb383ea;hb=c3d43aa1e221c74936adac7673f1923cbec5fdd0
>
> > I tried to translate what I think you intended in your code snippet to
> rust
> > which you can view the output generated on Compiler Explorer:
> > https://rust.godbolt.org/z/ydX-JH
>
>  appreciated... however taking that route would ultimately mean having
> an external call-out from spike (c++) to a rust math library, as the
> code, once tested (in rust) would then need to be used... in spike.
>
I didn't mean to use Rust in spike, I meant you could use Rust to check if
different operations were identical and then translate from rust back to C.

>
>  unless completely rewriting a new simulator entirely from scratch in
> rust.  at 16,000 lines of code i'm not keen on doing that, as it would
> require abandoning the hugely-tested spike codebase.
>
That would be a lot of work.

Jacob