Fix alignment of WASMER_METADATA in the dylib engine

rykv requires this to be at least 16-byte aligned.

lib/compiler-llvm/src/compiler.rs

@@ -172,6 +172,7 @@ impl LLVMCompiler {
         metadata_gv.set_initializer(&metadata_init);
         metadata_gv.set_linkage(Linkage::DLLExport);
         metadata_gv.set_dll_storage_class(DLLStorageClass::Export);
+        metadata_gv.set_alignment(16);
 
         if self.config().enable_verifier {
             merged_module.verify().unwrap();

lib/engine-dylib/src/artifact.rs

@@ -2,7 +2,7 @@
 //! to be done as separate steps.
 
 use crate::engine::{DylibEngine, DylibEngineInner};
-use crate::serialize::{ArchivedModuleMetadata, ModuleMetadata};
+use crate::serialize::ModuleMetadata;
 use enumset::EnumSet;
 use libloading::{Library, Symbol as LibrarySymbol};
 use loupe::MemoryUsage;
@@ -217,7 +217,7 @@ impl DylibArtifact {
 
         let serialized_data = metadata.serialize()?;
 
-        let mut metadata_binary = vec![0; 12];
+        let mut metadata_binary = vec![0; 16];
         let mut writable = &mut metadata_binary[..];
         leb128::write::unsigned(&mut writable, serialized_data.len() as u64)
             .expect("Should write number");
@@ -256,13 +256,8 @@ impl DylibArtifact {
                     function_body_inputs,
                 )?;
                 let mut obj = get_object_for_target(&target_triple).map_err(to_compile_error)?;
-                emit_data(
-                    &mut obj,
-                    WASMER_METADATA_SYMBOL,
-                    &metadata_binary,
-                    std::mem::align_of::<ArchivedModuleMetadata>() as u64,
-                )
-                .map_err(to_compile_error)?;
+                emit_data(&mut obj, WASMER_METADATA_SYMBOL, &metadata_binary, 16)
+                    .map_err(to_compile_error)?;
                 emit_compilation(&mut obj, compilation, &symbol_registry, &target_triple)
                     .map_err(to_compile_error)?;
                 let file = tempfile::Builder::new()
@@ -623,27 +618,24 @@ impl DylibArtifact {
             DeserializeError::CorruptedBinary(format!("Library loading failed: {}", e))
         })?;
         let shared_path: PathBuf = PathBuf::from(path);
-        // We use 12 + 1, as the length of the module will take 12 bytes
-        // (we construct it like that in `metadata_length`) and we also want
-        // to take the first element of the data to construct the slice from
-        // it.
-        let symbol: LibrarySymbol<*mut [u8; 12 + 1]> =
+        // We reserve 16 bytes for the length because the rest of the metadata
+        // needs to be aligned to 16 bytes.
+        let symbol: LibrarySymbol<*mut [u8; 16]> =
             lib.get(WASMER_METADATA_SYMBOL).map_err(|e| {
                 DeserializeError::CorruptedBinary(format!(
                     "The provided object file doesn't seem to be generated by Wasmer: {}",
                     e
                 ))
             })?;
-        use std::ops::Deref;
         use std::slice;
 
-        let size = &mut **symbol.deref();
-        let mut readable = &size[..];
+        let metadata = &**symbol;
+        let mut readable = &metadata[..];
         let metadata_len = leb128::read::unsigned(&mut readable).map_err(|_e| {
             DeserializeError::CorruptedBinary("Can't read metadata size".to_string())
         })?;
         let metadata_slice: &'static [u8] =
-            slice::from_raw_parts(&size[12] as *const u8, metadata_len as usize);
+            slice::from_raw_parts(metadata.as_ptr().add(16), metadata_len as usize);
 
         let metadata = ModuleMetadata::deserialize(metadata_slice)?;