Ok, here's the result: https://floooh.github.io/pacman.zig/pacman.html
Build instructions: https://github.com/floooh/pacman.zig#experimental-web-support ...and a quick explanation how it works, and what workarounds are currently required (and below that is the actual build function): https://github.com/floooh/pacman.zig/blob/549a73ecd6f5c9bfe4f8150b08e4b43f02eae331/build.zig#L44-L61 ...disclaimer: I'm not yet very familiar with the Zig build system which doesn't really support injecting a different linker, but that's the cleanest I came up with. Cheers and thanks for the help :) -Floh. On Sunday, 30 January 2022 at 01:16:44 UTC+1 [email protected] wrote: > I'm pretty sure EMSCRIPTEN_KEEPALIVE won't have the intended behaviour of > actually exporting symbols when compiled with non-emscripten triples. > > On Sat, Jan 29, 2022 at 4:08 PM Floh <[email protected]> wrote: > >> Thanks for the thorough explanation Sam! Regarding this PR: >> https://github.com/emscripten-core/emscripten/pull/16149, as far as I >> have seen, only the EM_JS() macros caused trouble (with a non-emscripten >> triple), I haven't seen any linker warnings regarding EMSCRIPTEN_KEEPALIVE >> functions (which I'm using too in the same code base). >> >> I'll try to bring the current workaround (use wasm32-emscripten just for >> the C code with the EM_JS macros, and wasm32-freestanding for the Zig >> code), into a better shape tomorrow and then will most likely write a Zig >> ticket, I think the Zig stdlib needs a few fixes for wasm32-emscripten (if >> just some empty stubs), so that a complete project can be compiled with >> this triple. >> >> Cheers! >> -Floh. >> >> On Saturday, 29 January 2022 at 20:47:24 UTC+1 [email protected] wrote: >> >>> Short term fix/wrokaround is here: >>> https://github.com/emscripten-core/emscripten/pull/16149 >>> >>> On Sat, Jan 29, 2022 at 11:32 AM Sam Clegg <[email protected]> wrote: >>> >>>> The undefined symbol error you are seeing here is coming from the >>>> post-linking phase. The way EM_JS works is that the function is that >>>> function `foo` declared as external using >>>> `__attribute__((import_name("foo")))` and the data symbol `__em_js_foo` is >>>> defined in the data section along with `__attribute__((used, >>>> visibility("default")))`. For more details on this see >>>> https://github.com/emscripten-core/emscripten/blob/main/system/include/emscripten/em_js.h#L23-L49 >>>> . >>>> >>>> I believe the problem you are seeing stems from the different meaning >>>> of `__attribute__((used))` under emscripten compared to with triples. >>>> The problem stems from the fact that we use `__attribute__((used))` to >>>> implement the EMSCRIPTEN_KEEPALIVE macro, which is defined to mean "keep >>>> this symbol alive *and* export it to JS under its symbol name". >>>> >>>> If you use wasm-objdump to look at an object file containing EM_JS >>>> symbols you will see them marked as both "no_strip" and "exported". For >>>> example: >>>> >>>> ``` >>>> - 38: D <__em_js__noarg> segment=0 offset=0 size=36 [ exported >>>> no_strip binding=global vis=default ] >>>> - 39: D <__em_js__noarg_int> segment=0 offset=36 size=55 [ exported >>>> no_strip binding=global vis=default ] >>>> - 40: D <__em_js__noarg_double> segment=0 offset=91 size=61 [ >>>> exported no_strip binding=global vis=default ] >>>> - 41: D <__em_js__intarg> segment=0 offset=152 size=41 [ exported >>>> no_strip binding=global vis=default ] >>>> ``` >>>> >>>> If you compile the same source using a non-emscripten triple you will >>>> see them only marked as `no_strip` which is a more traditional meaning of >>>> the `used` attribute which simply tells the linker to keep them around in >>>> the binary, not to export them. Here is where the hack/difference is: >>>> https://github.com/llvm/llvm-project/blob/333f5019300c6e56782374627e64da0b62ffa3bc/llvm/lib/MC/WasmObjectWriter.cpp#L1773-L1777 >>>> >>>> There are two ways we can solve this issue I believe. >>>> >>>> 1. Long term solution: Stop abusing `__attribute__((used))`, and thus >>>> remove this special handling in emscripten. We should really have a >>>> separate attribute to mark a symbol as exported. I've been trying to get >>>> this done for while but its stalled. See >>>> https://reviews.llvm.org/D76547 >>>> 2. Short term solution: Use the more explicit (but not >>>> EMSCIRPTEN_KEEPALIVE-compatible), 'export-name' attribute in em_js.h. I >>>> think this should "just work". >>>> >>>> cheers, >>>> sam >>>> >>>> >>>> On Sat, Jan 29, 2022 at 10:22 AM Floh <[email protected]> wrote: >>>> >>>>> Spot on Alon :) >>>>> >>>>> It works if I hardwire just the C library (with the EM_JS functions) >>>>> to the wasm32-emscripten triple. >>>>> >>>>> The Zig code needs to be compiled either with wasm32-wasi or >>>>> wasm32-freestanding, when using wasm32-emscripten, parts of the Zig >>>>> stdlib >>>>> won't compile. >>>>> >>>>> Also, when I tried to use wasm32-freestanding with the C code, then >>>>> wasm-ld complained about some missing stack-check functions (don't have >>>>> the >>>>> exact symbol at hand currently). >>>>> >>>>> ...I think I have enough to build a little 'proof-of-concept', even >>>>> though it's a bit hacky :) >>>>> >>>>> Thanks! >>>>> -Floh. >>>>> On Saturday, 29 January 2022 at 18:58:53 UTC+1 [email protected] >>>>> wrote: >>>>> >>>>>> Sam can confirm, but I would guess perhaps the emscripten triple is >>>>>> necessary. That is, clang and/or wasm-ld might do something for EM_JS >>>>>> code >>>>>> but only in emscripten mode. >>>>>> >>>>>> If we can confirm that then we should definitely get a bug filed on >>>>>> Zig - hopefully it would be easy to add support for the emscripten >>>>>> triple >>>>>> there and open up a bunch of use cases... >>>>>> >>>>>> On Sat, Jan 29, 2022 at 9:12 AM Floh <[email protected]> wrote: >>>>>> >>>>>>> I'm currently tinkering with bringing one of my toy Zig projects to >>>>>>> the web via >>>>>>> Alon's nice gist here which uses emcc only for the linker step: >>>>>>> >>>>>>> https://gist.github.com/kripken/58c0e640227fe5bac9e7b30100a2a1d3 >>>>>>> >>>>>>> ...and it *nearly* works except for code that uses EM_JS() macros. >>>>>>> >>>>>>> The project (https://github.com/floooh/pacman.zig) consists of some >>>>>>> C code (my cross-platform 'sokol headers') which uses EM_JS() quite >>>>>>> extensively (very handy for STB-style single-file libraries), and at >>>>>>> the >>>>>>> top, the "game code" is written in Zig. >>>>>>> >>>>>>> I'm compiling all code with Zig with the wasm32-wasi target >>>>>>> (wasm32-emscripten exists, but currently doesn't seem to be supported >>>>>>> by >>>>>>> the Zig compiler), and then use emcc for linking. >>>>>>> >>>>>>> Long story short, it works except for the one problem that emcc >>>>>>> cannot resolve any functions which have been defined with EM_JS(). If I >>>>>>> compile the same library with emcc instead of Zig it works. >>>>>>> >>>>>>> So my question is: does emcc also do some "EM_JS() magic" when >>>>>>> compiling the source code which contains EM_JS macros? Maybe I'm >>>>>>> missing >>>>>>> some Clang command line options which emcc inserts? >>>>>>> >>>>>>> The errors look like this: >>>>>>> >>>>>>> error: undefined symbol: sapp_js_add_clipboard_listener (referenced >>>>>>> by top-level compiled C/C++ code) >>>>>>> >>>>>>> Followed by: >>>>>>> >>>>>>> warning: _sapp_js_add_clipboard_listener may need to be added to >>>>>>> EXPORTED_FUNCTIONS if it arrives from a system library >>>>>>> ...there's also a single warning about malloc: >>>>>>> >>>>>>> ...if I compile with "-s ERROR_ON_UNDEFINED_SYMBOLS=0", then the >>>>>>> code breaks at runtime failing to resolve those EM_JS() functions, e.g.: >>>>>>> >>>>>>> "missing function: sapp_js_pointer_init" >>>>>>> >>>>>>> Compiling the same static link library with emcc, it magically works. >>>>>>> >>>>>>> If I look at both libraries with nm I don't see much of a >>>>>>> difference, e.g. here's the relevant parts from the emcc-compiled >>>>>>> library, >>>>>>> every EM_JS symbol has an "D __em_js..." entry, and a matching "U >>>>>>> sapp_js..." entry, e.g.: >>>>>>> >>>>>>> 0000185f D __em_js__sapp_js_add_beforeunload_listener >>>>>>> ... >>>>>>> U sapp_js_add_beforeunload_listener >>>>>>> ... >>>>>>> >>>>>>> The Zig-compiled library has the same entries: >>>>>>> >>>>>>> 00001841 D __em_js__sapp_js_add_beforeunload_listener >>>>>>> ... >>>>>>> U sapp_js_add_beforeunload_listener >>>>>>> ... >>>>>>> >>>>>>> ...yet one library (the zig-compiled) produces linker errors for >>>>>>> those symbols, and the other (emcc-compiled) works. >>>>>>> >>>>>>> Clearly I'm missing something. I was expecting that all the EM_JS() >>>>>>> magic is in the linker (by extracting the __em_js_* Javascript source >>>>>>> code >>>>>>> strings, and then "somehow" providing the C function import). Any ideas >>>>>>> what I'm missing? >>>>>>> >>>>>>> Thanks! >>>>>>> -Floh. >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> -- >>>>>>> You received this message because you are subscribed to the Google >>>>>>> Groups "emscripten-discuss" group. >>>>>>> To unsubscribe from this group and stop receiving emails from it, >>>>>>> send an email to [email protected]. >>>>>>> To view this discussion on the web visit >>>>>>> https://groups.google.com/d/msgid/emscripten-discuss/15129292-2f07-44d9-99a9-a27ac4721a0cn%40googlegroups.com >>>>>>> >>>>>>> <https://groups.google.com/d/msgid/emscripten-discuss/15129292-2f07-44d9-99a9-a27ac4721a0cn%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>>>> . >>>>>>> >>>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "emscripten-discuss" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to [email protected]. >>>>> To view this discussion on the web visit >>>>> https://groups.google.com/d/msgid/emscripten-discuss/ad13a6a8-0248-406d-ba91-591bcec62e54n%40googlegroups.com >>>>> >>>>> <https://groups.google.com/d/msgid/emscripten-discuss/ad13a6a8-0248-406d-ba91-591bcec62e54n%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>> . >>>>> >>>> -- >> You received this message because you are subscribed to the Google Groups >> "emscripten-discuss" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> > To view this discussion on the web visit >> https://groups.google.com/d/msgid/emscripten-discuss/75b6eb8b-f6a3-4ce8-a075-462f1902e087n%40googlegroups.com >> >> <https://groups.google.com/d/msgid/emscripten-discuss/75b6eb8b-f6a3-4ce8-a075-462f1902e087n%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- You received this message because you are subscribed to the Google Groups "emscripten-discuss" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/emscripten-discuss/65b49e25-0011-4cd1-8aa6-64bd38f4317cn%40googlegroups.com.
