Emscripten: [LLVM backend regression] RuntimeError: unreachable

[buu700]

I just had to rebuild sidh.js with latest-fastcomp to work around an error caused by latest-upstream.

With the following test case:

git clone https://github.com/cyph/sidh.js
cd sidh.js
make
node -e "require('./dist/sidh').keyPair().then(kp => console.log(kp))"

The make succeeds, but then I get the following unexpected run-time error:

RuntimeError: unreachable
RuntimeError: unreachable

/cyph/dist/sidh.js:1
var sidh=function(){var A,I,g,B,C={};function Q(A,I){if(0===A)return I;throw new Error("SIDH error: "+A)}function i(A,I){return new Uint8Array(new Uint8Array(C.HEAPU8.buffer,A,I))}function E(A){try{C._free(A)}catch(A){setTimeout((function(){throw A}),0)}}C.ready=new Promise((function(A,I){(B={}).onAbort=I,B.onRuntimeInitialized=function(){try{B._sidhjs_public_key_bytes(),A(B)}catch(A){I(A)}};var g,B=void 0!==B?B:{},C={};for(g in B)B.hasOwnProperty(g)&&(C[g]=B[g]);var Q=[],i=!1,E=!1,o=!1,a=!1,G=!1;i="object"==typeof window,E="function"==typeof importScripts,a="object"==typeof process&&"object"==typeof process.versions&&"string"==typeof process.versions.node,o=a&&!i&&!E,G=!i&&!o&&!E;var n,r,c,t,D="";function e(A){return B.locateFile?B.locateFile(A,D):D+A}o?(D=__dirname+"/",n=function(A,I){var g;return(g=YA(A))||(c||(c=eval("require")("fs")),t||(t=eval("require")("path")),A=t.normalize(A),g=c.readFileSync(A)),I?g:g.toString()},r=function(A){var I=n(A,!0);return I.buffer||(I=new Uint8Array(
abort(RuntimeError: unreachable). Build with -s ASSERTIONS=1 for more info.

This problem goes away after running emsdk install latest-fastcomp ; emsdk activate latest-fastcomp ; make.

[kripken]

A full stack trace (in a build with names, so e.g. --profiling) might help. Also good would be to bisect to find where this broke.

[TrevorSundberg]

This is potentially unrelated, however I also received the RuntimeError: unreachable and it turned out it was because a missing return statement when the function returned a bool. Hope this helps some poor soul in the future. Also don't ignore warnings!

[davlhd]

I am experiencing the same problem. I wanted to switch to the new backend but it tells me

011245ce-331:8 Uncaught (in promise) RuntimeError: unreachable.
at wasm-function[331]:0x13538
at wasm-function[11511]:0x2356e3
at n.dynCall_iiiiiii (https://xxx35:156437)
at invoke_iiiiiii (https://xxs:35:102325)
at wasm-function[14939]:0x3ae4f3
at wasm-function[11508]:0x235501
at n.dynCall_iiiiiiiii (https://xxxs:35:156969)
at invoke_iiiiiiiii (https://xxx:35:102612)
at wasm-function[14865]:0x3ab14e

[kripken]

@davlhd building with --profiling will make the stack trace have function names.

Once you find the function this happens in, it might be the same issue @TrevorSundberg said - LLVM will emit unreachables in places it thinks control flow can't reach, so if you forget a return, stuff like that.

[davlhd]

That did no really help:

00ceb43a:formatted:403 Uncaught (in promise) RuntimeError: unreachable
    at <anonymous>:wasm-function[285]:0xf851
    at dynCall_iiiiiii (<anonymous>:wasm-function[7519]:0x170aa2)
    at i.dynCall_iiiiiii (https://xxxx:35:140187)
    at invoke_iiiiiii (https://xxxx35:116645)
    at <anonymous>:wasm-function[9936]:0x2be4fd
    at dynCall_iiiiiiiii (<anonymous>:wasm-function[7517]:0x170a78)
    at i.dynCall_iiiiiiiii (https://xxxx:35:140719)
    at invoke_iiiiiiiii (https://xxxx:35:116932)
    at <anonymous>:wasm-function[9087]:0x24ae07
    at dynCall_iiiiii (<anonymous>:wasm-function[7520]:0x170ab4)

[kripken]

@davlhd is there a chance the --profiling flag was not applied at the link stage? Or that that's an old build? (It would be a very serious unknown bug if that didn't work.)

[davlhd]

With "latest" this error disappeared. It now compiles and runs fine