Hopefully finish the memory manager implementation for llvm RuntimeDyLd

lib/llvm-backend/src/platform/unix/mod.rs

@@ -0,0 +1,40 @@
+
+extern "C" {
+    fn __register_frame(frame: *const u8);
+    fn __deregister_frame(frame: *const u8);
+}
+
+pub unsafe fn register_eh_frames(eh_frames: *const u8, num_bytes: usize) {
+    visit_frame_desc_entries(eh_frames, num_bytes, |frame| __register_frame(frame));
+}
+
+unsafe fn visit_frame_desc_entries<F>(eh_frames: *const u8, num_bytes: usize, visitor: F)
+where
+    F: Fn(*const u8),
+{
+    let mut next = eh_frames;
+    let mut end = eh_frames.add(num_bytes);
+
+    loop {
+        if next >= end {
+            break;
+        }
+
+        let cfi = next;
+        let mut cfi_num_bytes = (next as *const u32).read_unaligned() as u64;
+        assert!(cfi_num_bytes != 0);
+
+        next = next.add(4);
+        if num_bytes == 0xffffffff {
+            let cfi_num_bytes64 = (next as *const u64).read_unaligned();
+            cfi_num_bytes = cfi_num_bytes64;
+            next = next.add(8);
+        }
+
+        let cie_offset = (next as *const u32).read_unaligned();
+        if cie_offset != 0 {
+            visitor(cfi);
+        }
+        next = next.add(cfi_num_bytes as usize);
+    }
+}