Disable SIMD when compiling smoldot (#903)

* Disable SIMD when compiling smoldot

* PR link

* Comment tweak

wasm-node/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### Changed
+
+- The smoldot binary now longer has SIMD enabled, in order to make it work on a greater range of hardware. It was previously assumed that SIMD instructions were emulated on hardware that doesn't natively support them, but this doesn't seem to be the case for some browser engines. ([#903](https://github.com/smol-dot/smoldot/pull/903))
+
 ## 1.0.12 - 2023-07-10
 
 ### Changed

wasm-node/javascript/prepare.mjs

@@ -64,6 +64,10 @@ child_process.execSync(
 // code. This generates a `wasm` file in `target/wasm32-wasi`.
 // Some optional Wasm features are enabled during the compilation in order to speed up the
 // execution of smoldot.
+// SIMD is intentionally not enabled, because WASM engines seem to allow only SIMD instructions
+// on specific hardware. See for example <https://bugzilla.mozilla.org/show_bug.cgi?id=1625130#c11>
+// and <https://bugzilla.mozilla.org/show_bug.cgi?id=1840710>.
+//
 // Note that this doesn't enable these features in the Rust standard library (which comes
 // precompiled), but the missing optimizations shouldn't be too much of a problem. The Rust
 // standard library could be compiled with these features using the `-Z build-std` flag, but at
@@ -75,7 +79,7 @@ child_process.execSync(
 child_process.execSync(
     "cargo +" + rustVersion + " build --package smoldot-light-wasm --target wasm32-wasi --no-default-features " +
     (buildProfile == 'debug' ? '' : ("--profile " + buildProfile)),
-    { 'stdio': 'inherit', 'env': { 'RUSTFLAGS': '-C target-feature=+bulk-memory,+sign-ext,+simd128', ...process.env } }
+    { 'stdio': 'inherit', 'env': { 'RUSTFLAGS': '-C target-feature=+bulk-memory,+sign-ext', ...process.env } }
 );
 const rustOutput = "../../target/wasm32-wasi/" + buildProfile + "/smoldot_light_wasm.wasm";