[fpc-devel] WebAssembly compilation problems - Wasm32 symbol xxx without index value error

[Nikolay Nikolov]

On 3/28/23 02:12, Michalis Kamburelis via fpc-devel wrote:
> Hi,
>
> We're experimenting with compiling Castle Game Engine using FPC
> WebAssembly target.
>
> A lot of units and classes compiled smoothly, however we hit a weird
> bug(s) at compiling our (big, too big!) unit X3DNodes. We get errors
> "Wasm32 symbol xxx without index value error" at the code trying to
> use various property setters or methods. Examples:
>
> x3dcamerautils.pas(344,0) Error: Wasm32 symbol
> X3DFIELDS$_$TSFROTATION_$__$$_SETVALUE$TGENERICVECTOR4 without index
> value error
>
> // where TSFRotation.Value is a property with record type, with getter
> and setter methods
>
> x3dcamerautils.pas(344,0) Error: Wasm32 symbol
> X3DFIELDS$_$TX3DSIMPLEMULTFIELD$3$CRCD1E2ED59_CRCAB5A7799_$__$$_GETITEMS$$TSINGLELIST
> without index value error
>
> // where TX3DSimpleMultField.GetItems is a method of a generic class)
>
> x3dcamerautils.pas(344,0) Error: Wasm32 symbol
> X3DFIELDS$_$TSFFLOAT_$__$$_SETVALUE$SINGLE without index value error
> x3dcamerautils.pas(344,0) Error: Wasm32 symbol
>
> // where TSFFloat.SetValue is a simple setter for a Single property, no generics
>
> castlescenecore.pas(8822,0) Error: Wasm32 symbol
> CASTLESHAPEINTERNALSHADOWVOLUMES$_$TSHAPESHADOWVOLUMES_$__$$_PREPARERESOURCES
> without index value error
>
> // where TShapeShadowVolumes.PrepareResources is a simple method,
> without any parameters, in a simple non-generic class
>
> Weirder, on another machine, the symbols reported contain some exe
> filenames at the place of initial "$_$" (maybe independent compiler
> bug at message display?):
>
> x3dloadinternalgeo.pas(234,0) Error: Wasm32 symbol
> X3DFIELDS/usr/bin/dbus-update-activation-environmentTSFFLOAT_$__$$_SETVALUE$SINGLE
> without index value error
>
> x3dloadinternalgeo.pas(234) Error: Wasm32 symbol
> X3DFIELDS/home/michalis/bin/castle-engineTSFFLOAT_$__$$_SETVALUE$SINGLE
> without index value error
>
> Sometimes the errors can be workarounded by some simple actions --
> like moving the property getter/setter protected->private, or avoiding
> the call to that particular method. But the solutions, as well as
> causes, seem ~random from our perspective. And all in all, we didn't
> finish the compilation of X3DNodes unit because after each
> fix/workaround/hack for a specific case, another similar error pops
> up.
>
> Grepping FPC for the asmw_e_illegal_unset_index (this is "Wasm32
> symbol $1 without index value error"), the error can occur when symbol
> cannot be found in the list where compiler expected it to be.
>
> We don't have any simple bugreport about it (yet), as the error really
> manifests only in a big unit, that is interconnected with a few other
> big units. Isolating the testcase (and/or doing much needed refactor
> of this unit :) ) will take a while.
>
> Does anyone have a hint:
>
> - What does this error really mean? What is internally wrong at
> compilation to cause it? What could be the culprit?
>
> - Is there some universal workaround for it (on CGE side) or fix on
> the compiler side?
>
> Even a vague hint could at least help us prepare an isolated
> bugreport, because otherwise we have a rather big chunk of code to
> dissect in order to provide a simple FPC testcase :)

Even a big unit is fine for a bug report, as long as all the code is 
publicly available for download. If you can't seem to get it to 
reproduce with a small test case, you can mention in the bug report that 
you tried, but didn't succeed and still provide the full code needed. 
AFAIK, the Castle Game Engine is open-source, so this shouldn't be a 
problem?

Nikolay

>
> Regards,
> Michalis
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