feat: add a histrical wit-bindgen

__wasm/wit-bindgen-sample/wit-bindgen/crates/gen-spidermonkey/src/data_segments.rs

@@ -0,0 +1,72 @@
+//! Assigning static locations for data segments we will emit in the glue Wasm
+//! module.
+
+use std::convert::TryFrom;
+
+#[derive(Debug)]
+pub struct DataSegments {
+    data: wasm_encoder::DataSection,
+    next_offset: u32,
+    memory: u32,
+}
+
+impl DataSegments {
+    /// Create a new collection of data segments for the given memory.
+    pub fn new(memory: u32) -> DataSegments {
+        DataSegments {
+            data: wasm_encoder::DataSection::new(),
+            next_offset: 0,
+            memory,
+        }
+    }
+
+    /// Add a new segment to this `DataSegments`, returning the assigned offset
+    /// in memory.
+    pub fn add<S>(&mut self, segment: S) -> u32
+    where
+        S: IntoIterator<Item = u8>,
+        S::IntoIter: ExactSizeIterator,
+    {
+        let segment = segment.into_iter();
+        let offset = self.reserve_space(u32::try_from(segment.len()).unwrap());
+        self.data.active(
+            self.memory,
+            &wasm_encoder::Instruction::I32Const(offset as i32),
+            segment,
+        );
+        offset
+    }
+
+    /// Reserve space in memory but don't emit any data segment to initialize
+    /// it.
+    ///
+    /// This effectively lets you add zero-initialized data segments, reserve
+    /// space for return pointer areas, or define shadow stack regions.
+    pub fn reserve_space(&mut self, num_bytes: u32) -> u32 {
+        // Leave an empty byte between each data segment. This helps when
+        // staring at disassemblies and heap dumps.
+        self.next_offset += 1;
+
+        let offset = self.next_offset;
+        self.next_offset += num_bytes;
+
+        offset
+    }
+
+    /// Get the memory type required to hold these data segments.
+    pub fn memory_type(&self) -> wasm_encoder::MemoryType {
+        const WASM_PAGE_SIZE: u32 = 65_536;
+        wasm_encoder::MemoryType {
+            minimum: ((self.next_offset + WASM_PAGE_SIZE - 1) / WASM_PAGE_SIZE).into(),
+            maximum: None,
+            memory64: false,
+        }
+    }
+
+    /// Take the constructed data section.
+    ///
+    /// No more data segments should be added after this is called.
+    pub fn take_data(&mut self) -> wasm_encoder::DataSection {
+        std::mem::replace(&mut self.data, wasm_encoder::DataSection::new())
+    }
+}