First baby steps to supporting memory accesses

Currently we don't actually sandbox the memory at all, so you can do evil things
like read and write the host's memory. We also don't support growing memory or
cranelift-compatible ABI that passes the memory offset as an argument.

We also always immediately allocate the buffer when encountering a memory section,
there is preliminary support for translating a buffer which can then have the real
offset replaced using relocations (and returning a different type when doing so)
but I haven't written the code that actually does relocation so it doesn't work yet.

src/translate_sections.rs

@@ -45,11 +45,11 @@ pub fn table(tables: TableSectionReader) -> Result<(), Error> {
 }
 
 /// Parses the Memory section of the wasm module.
-pub fn memory(memories: MemorySectionReader) -> Result<(), Error> {
-    for entry in memories {
-        entry?; // TODO
-    }
-    Ok(())
+pub fn memory(memories: MemorySectionReader) -> Result<Vec<MemoryType>, Error> {
+    memories
+        .into_iter()
+        .map(|r| r.map_err(Into::into))
+        .collect()
 }
 
 /// Parses the Global section of the wasm module.
@@ -86,13 +86,22 @@ pub fn element(elements: ElementSectionReader) -> Result<(), Error> {
 pub fn code(
     code: CodeSectionReader,
     translation_ctx: &TranslationContext,
+    memory: Option<&mut [u8]>,
 ) -> Result<TranslatedCodeSection, Error> {
     let func_count = code.get_count();
-    let mut session = CodeGenSession::new(func_count);
-    for (idx, body) in code.into_iter().enumerate() {
-        function_body::translate(&mut session, translation_ctx, idx as u32, &body?)?;
+    if let Some(memory) = memory {
+        let mut session = CodeGenSession::<::backend::HasMemory>::with_memory(func_count, memory.as_mut_ptr());
+        for (idx, body) in code.into_iter().enumerate() {
+            function_body::translate(&mut session, translation_ctx, idx as u32, &body?)?;
+        }
+        Ok(session.into_translated_code_section()?)
+    } else {
+        let mut session = CodeGenSession::<::backend::NoMemory>::new(func_count);
+        for (idx, body) in code.into_iter().enumerate() {
+            function_body::translate(&mut session, translation_ctx, idx as u32, &body?)?;
+        }
+        Ok(session.into_translated_code_section()?)
     }
-    Ok(session.into_translated_code_section()?)
 }
 
 /// Parses the Data section of the wasm module.