cranelift: Add heap support to filetest infrastructure (#3154)

* cranelift: Add heap support to filetest infrastructure

* cranelift: Explicit heap pointer placement in filetest annotations

* cranelift: Add documentation about the Heap directive

* cranelift: Clarify that heap filetests pointers must be laid out sequentially

* cranelift: Use wrapping add when computing bound pointer

* cranelift: Better error messages when invalid signatures are found for heap file tests.

cranelift/filetests/src/runtest_environment.rs

@@ -0,0 +1,111 @@
+use anyhow::anyhow;
+use cranelift_codegen::data_value::DataValue;
+use cranelift_codegen::ir::Type;
+use cranelift_reader::parse_heap_command;
+use cranelift_reader::{Comment, HeapCommand};
+
+/// Stores info about the expected environment for a test function.
+#[derive(Debug, Clone)]
+pub struct RuntestEnvironment {
+    pub heaps: Vec<HeapCommand>,
+}
+
+impl RuntestEnvironment {
+    /// Parse the environment from a set of comments
+    pub fn parse(comments: &[Comment]) -> anyhow::Result<Self> {
+        let mut env = RuntestEnvironment { heaps: Vec::new() };
+
+        for comment in comments.iter() {
+            if let Some(heap_command) = parse_heap_command(comment.text)? {
+                let heap_index = env.heaps.len() as u64;
+                let expected_ptr = heap_index * 16;
+                if Some(expected_ptr) != heap_command.ptr_offset.map(|p| p.into()) {
+                    return Err(anyhow!(
+                        "Invalid ptr offset, expected vmctx+{}",
+                        expected_ptr
+                    ));
+                }
+
+                let expected_bound = (heap_index * 16) + 8;
+                if Some(expected_bound) != heap_command.bound_offset.map(|p| p.into()) {
+                    return Err(anyhow!(
+                        "Invalid bound offset, expected vmctx+{}",
+                        expected_bound
+                    ));
+                }
+
+                env.heaps.push(heap_command);
+            };
+        }
+
+        Ok(env)
+    }
+
+    pub fn is_active(&self) -> bool {
+        !self.heaps.is_empty()
+    }
+
+    /// Allocates a struct to be injected into the test.
+    pub fn runtime_struct(&self) -> RuntestContext {
+        RuntestContext::new(&self)
+    }
+}
+
+type HeapMemory = Vec<u8>;
+
+/// A struct that provides info about the environment to the test
+#[derive(Debug, Clone)]
+pub struct RuntestContext {
+    /// Store the heap memory alongside the context info so that we don't accidentally deallocate
+    /// it too early.
+    heaps: Vec<HeapMemory>,
+
+    /// This is the actual struct that gets passed into the `vmctx`  argument of the tests.
+    /// It has a specific memory layout that all tests agree with.
+    ///
+    /// Currently we only have to store heap info, so we store the heap start and end addresses in
+    /// a 64 bit slot for each heap.
+    ///
+    /// ┌────────────┐
+    /// │heap0: start│
+    /// ├────────────┤
+    /// │heap0: end  │
+    /// ├────────────┤
+    /// │heap1: start│
+    /// ├────────────┤
+    /// │heap1: end  │
+    /// ├────────────┤
+    /// │etc...      │
+    /// └────────────┘
+    context_struct: Vec<u64>,
+}
+
+impl RuntestContext {
+    pub fn new(env: &RuntestEnvironment) -> Self {
+        let heaps: Vec<HeapMemory> = env
+            .heaps
+            .iter()
+            .map(|cmd| {
+                let size: u64 = cmd.size.into();
+                vec![0u8; size as usize]
+            })
+            .collect();
+
+        let context_struct = heaps
+            .iter()
+            .flat_map(|heap| [heap.as_ptr(), heap.as_ptr().wrapping_add(heap.len())])
+            .map(|p| p as usize as u64)
+            .collect();
+
+        Self {
+            heaps,
+            context_struct,
+        }
+    }
+
+    /// Creates a [DataValue] with a target isa pointer type to the context struct.
+    pub fn pointer(&self, ty: Type) -> DataValue {
+        let ptr = self.context_struct.as_ptr() as usize as i128;
+        DataValue::from_integer(ptr, ty).expect("Failed to cast pointer to native target size")
+    }
+}