> Btw, did you get a chance to file a Zig ticket as you said? Haven't done that yet!
On Monday, 31 January 2022 at 18:51:07 UTC+1 [email protected] wrote: > Nice, good to see pacman working! > > Btw, did you get a chance to file a Zig ticket as you said? > > > On Mon, Jan 31, 2022 at 1:53 AM Floh <[email protected]> wrote: > >> PS: the missing __stack_chk_* symbol errors I mentioned formerly are >> unrelated to the target triple, but instead happen when compiling via Zig >> in debug mode. In that case, Zig compiles the C code with clang's >> "-fstack-protector-strong" which requires two externally defined symbols, a >> guard-value and a function which is called when the stack protection >> triggers. When linking with emcc those symbols can't be found, so I just >> provided them myself in the C stub here: >> >> https://github.com/floooh/pacman.zig/blob/main/src/emscripten/entry.c >> >> On Sunday, 30 January 2022 at 17:56:32 UTC+1 Floh wrote: >> >>> 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/30ce1142-720c-4acf-b3d9-a3b1630ea2c3n%40googlegroups.com >> >> <https://groups.google.com/d/msgid/emscripten-discuss/30ce1142-720c-4acf-b3d9-a3b1630ea2c3n%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- You received this message because you are subscribed to the Google Groups "emscripten-discuss" group. 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