1 files changed, 136 insertions, 0 deletions
diff --git a/compiler/rustc_codegen_cranelift/src/debuginfo/unwind.rs b/compiler/rustc_codegen_cranelift/src/debuginfo/unwind.rs
new file mode 100644
index 000000000..d26392c49
--- /dev/null
+++ b/compiler/rustc_codegen_cranelift/src/debuginfo/unwind.rs
@@ -0,0 +1,136 @@
+//! Unwind info generation (`.eh_frame`)
+
+use crate::prelude::*;
+
+use cranelift_codegen::ir::Endianness;
+use cranelift_codegen::isa::{unwind::UnwindInfo, TargetIsa};
+
+use cranelift_object::ObjectProduct;
+use gimli::write::{Address, CieId, EhFrame, FrameTable, Section};
+use gimli::RunTimeEndian;
+
+use super::object::WriteDebugInfo;
+
+pub(crate) struct UnwindContext {
+    endian: RunTimeEndian,
+    frame_table: FrameTable,
+    cie_id: Option<CieId>,
+}
+
+impl UnwindContext {
+    pub(crate) fn new(isa: &dyn TargetIsa, pic_eh_frame: bool) -> Self {
+        let endian = match isa.endianness() {
+            Endianness::Little => RunTimeEndian::Little,
+            Endianness::Big => RunTimeEndian::Big,
+        };
+        let mut frame_table = FrameTable::default();
+
+        let cie_id = if let Some(mut cie) = isa.create_systemv_cie() {
+            if pic_eh_frame {
+                cie.fde_address_encoding =
+                    gimli::DwEhPe(gimli::DW_EH_PE_pcrel.0 | gimli::DW_EH_PE_sdata4.0);
+            }
+            Some(frame_table.add_cie(cie))
+        } else {
+            None
+        };
+
+        UnwindContext { endian, frame_table, cie_id }
+    }
+
+    pub(crate) fn add_function(&mut self, func_id: FuncId, context: &Context, isa: &dyn TargetIsa) {
+        let unwind_info = if let Some(unwind_info) = context.create_unwind_info(isa).unwrap() {
+            unwind_info
+        } else {
+            return;
+        };
+
+        match unwind_info {
+            UnwindInfo::SystemV(unwind_info) => {
+                self.frame_table.add_fde(
+                    self.cie_id.unwrap(),
+                    unwind_info
+                        .to_fde(Address::Symbol { symbol: func_id.as_u32() as usize, addend: 0 }),
+                );
+            }
+            UnwindInfo::WindowsX64(_) => {
+                // FIXME implement this
+            }
+            unwind_info => unimplemented!("{:?}", unwind_info),
+        }
+    }
+
+    pub(crate) fn emit(self, product: &mut ObjectProduct) {
+        let mut eh_frame = EhFrame::from(super::emit::WriterRelocate::new(self.endian));
+        self.frame_table.write_eh_frame(&mut eh_frame).unwrap();
+
+        if !eh_frame.0.writer.slice().is_empty() {
+            let id = eh_frame.id();
+            let section_id = product.add_debug_section(id, eh_frame.0.writer.into_vec());
+            let mut section_map = FxHashMap::default();
+            section_map.insert(id, section_id);
+
+            for reloc in &eh_frame.0.relocs {
+                product.add_debug_reloc(&section_map, &section_id, reloc);
+            }
+        }
+    }
+
+    #[cfg(all(feature = "jit", windows))]
+    pub(crate) unsafe fn register_jit(self, _jit_module: &cranelift_jit::JITModule) {}
+
+    #[cfg(all(feature = "jit", not(windows)))]
+    pub(crate) unsafe fn register_jit(self, jit_module: &cranelift_jit::JITModule) {
+        use std::mem::ManuallyDrop;
+
+        let mut eh_frame = EhFrame::from(super::emit::WriterRelocate::new(self.endian));
+        self.frame_table.write_eh_frame(&mut eh_frame).unwrap();
+
+        if eh_frame.0.writer.slice().is_empty() {
+            return;
+        }
+
+        let mut eh_frame = eh_frame.0.relocate_for_jit(jit_module);
+
+        // GCC expects a terminating "empty" length, so write a 0 length at the end of the table.
+        eh_frame.extend(&[0, 0, 0, 0]);
+
+        // FIXME support unregistering unwind tables once cranelift-jit supports deallocating
+        // individual functions
+        let eh_frame = ManuallyDrop::new(eh_frame);
+
+        // =======================================================================
+        // Everything after this line up to the end of the file is loosely based on
+        // https://github.com/bytecodealliance/wasmtime/blob/4471a82b0c540ff48960eca6757ccce5b1b5c3e4/crates/jit/src/unwind/systemv.rs
+        #[cfg(target_os = "macos")]
+        {
+            // On macOS, `__register_frame` takes a pointer to a single FDE
+            let start = eh_frame.as_ptr();
+            let end = start.add(eh_frame.len());
+            let mut current = start;
+
+            // Walk all of the entries in the frame table and register them
+            while current < end {
+                let len = std::ptr::read::<u32>(current as *const u32) as usize;
+
+                // Skip over the CIE
+                if current != start {
+                    __register_frame(current);
+                }
+
+                // Move to the next table entry (+4 because the length itself is not inclusive)
+                current = current.add(len + 4);
+            }
+        }
+        #[cfg(not(target_os = "macos"))]
+        {
+            // On other platforms, `__register_frame` will walk the FDEs until an entry of length 0
+            __register_frame(eh_frame.as_ptr());
+        }
+    }
+}
+
+extern "C" {
+    // libunwind import
+    fn __register_frame(fde: *const u8);
+}