From fed6ae454f659f4d2b36520474d1998b526a27dd Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Mon, 27 Feb 2023 22:00:11 +0100
Subject: Add JMP, JZ, and Label

---
 src/label.rs | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 src/label.rs

(limited to 'src/label.rs')

diff --git a/src/label.rs b/src/label.rs
new file mode 100644
index 0000000..b1f1133
--- /dev/null
+++ b/src/label.rs
@@ -0,0 +1,72 @@
+use std::collections::HashSet;
+
+/// A label which is used as target for jump instructions.
+///
+/// ```rust
+/// use juicebox_asm::prelude::*;
+///
+/// let mut lbl = Label::new();
+/// let mut asm = Asm::new();
+///
+/// // Skip the mov instruction.
+/// asm.jmp(&mut lbl);
+/// asm.mov(Reg64::rax, Reg64::rax);
+/// asm.bind(&mut lbl);
+/// ```
+///
+/// # Panics
+///
+/// Panics if the label is dropped while not yet bound, or having unresolved relocations.
+/// This is mainly a safety-guard to detect wrong usage.
+pub struct Label {
+    /// Location of the label. Will be set after the label is bound, else None.
+    location: Option<usize>,
+
+    /// Offsets that must be patched with the label location.
+    offsets: HashSet<usize>,
+}
+
+impl Label {
+    /// Create a new `unbound` [Label].
+    pub fn new() -> Label {
+        Label {
+            location: None,
+            offsets: HashSet::new(),
+        }
+    }
+
+    /// Bind the label to the `location`.
+    pub(crate) fn bind(&mut self, loc: usize) {
+        // A label can only be bound once!
+        assert!(!self.is_bound());
+
+        self.location = Some(loc);
+    }
+
+    /// Record an offset that must be patched with the label location.
+    pub(crate) fn record_offset(&mut self, off: usize) {
+        self.offsets.insert(off);
+    }
+
+    pub(crate) fn location(&self) -> Option<usize> {
+        self.location
+    }
+
+    pub(crate) fn offsets_mut(&mut self) -> &mut HashSet<usize> {
+        &mut self.offsets
+    }
+
+    /// Check whether the label is bound to a location.
+    const fn is_bound(&self) -> bool {
+        self.location.is_some()
+    }
+}
+
+impl Drop for Label {
+    fn drop(&mut self) {
+        // Ensure the label was bound when it is dropped.
+        assert!(self.is_bound());
+        // Ensure all offsets have been patched when the label is dropped.
+        assert!(self.offsets.is_empty());
+    }
+}
-- 
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