On Mon, Oct 5, 2020 at 10:19 AM Konrad Schwarz <[email protected]> wrote:
>
> To support a product based on the Intel Quark, which only has an x87 FPU and 
> no MMX/SSE/AVX, a colleague of mine resurrected the x87 port.
>
> This was done successfully for node.js version 8 -- unfortunately, I don't 
> know to which V8 version this corresponds to exactly, because the node.js 
> code base copies the V8 files rather than incorporating the V8 repository as 
> a submodule.
>
> I've attempted to move the patch forward to node.js version 10.  (One of the 
> primary new features for V8 was the Liftoff compiler for WASM; the garbage 
> collector has changed as well).  Unfortunately, I am getting an assertion 
> error during the "mksnapshot" build step:
>
> # Fatal error in ../deps/v8/src/compiler/register-allocator.cc, line 2663
> # Debug check failed: start_instr <= end_instr (80 vs. 0).
> #
> #
> #
> #FailureMessage Object: 0xffa80374
>
> As can be expected, this is happening while AllocateFPRegistersPhase() is 
> active (on the call stack).
>
> The V8 x87 port basically uses only one of the (stack-addressed) x87 
> registers, so on the one hand it would not be surprising for the register 
> allocator to have problems here.  On the other hand, this part of the code 
> has not changed much between the node.js v8 and v10, which indicates a 
> problem that I introduced.
>
> Any pointers or hints would be very much appreciated!

Not a direct answer to your question but you can find out the V8
version with `node -p process.versions.v8` or by looking at
deps/v8/include/v8-version.h.

For the last v8.x release, that's V8 6.2.78, for v10.x that's 6.8.32.
Both are pretty ancient by now, the latest major/minor is 8.8.x.

As to that debug check you're hitting, try starting node with `node
--trace_alloc script.js` - that should hopefully shed a clue where the
bad live range comes from.

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