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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