Fix binary parser of declarative element segments (#6618)

The parser was incorrectly handling the parsing of declarative element segments whose `init` is a `vec(expr)`.
https://webassembly.github.io/spec/core/binary/modules.html#element-section
Binry parser was simply reading a single `u32LEB` value for `init`
instead of parsing a expression regardless `usesExpressions = true`.

This commit updates the `WasmBinaryReader::readElementSegments` function
to correctly parse the expressions for declarative element segments by
calling `readExpression` instead of `getU32LEB` when `usesExpressions = true`.

Resolves the parsing exception:
"[parse exception: bad section size, started at ... not being equal to new position ...]"

Related discussion: https://github.com/tanishiking/scala-wasm/issues/136

1 files changed, 5 insertions, 1 deletions

diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index 805af1892..32dcc883a 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -3369,7 +3369,11 @@ void WasmBinaryReader::readElementSegments() {
       [[maybe_unused]] auto type = getU32LEB();
       auto num = getU32LEB();
       for (Index i = 0; i < num; i++) {
-        getU32LEB();
+        if (usesExpressions) {
+          readExpression();
+        } else {
+          getU32LEB();
+        }
       }
       continue;
     }