3 use cranelift_codegen::isa::{TargetIsa, unwind::UnwindInfo};
5 use gimli::write::{Address, CieId, EhFrame, FrameTable, Section};
7 use crate::backend::WriteDebugInfo;
9 pub(crate) struct UnwindContext<'tcx> {
11 frame_table: FrameTable,
12 cie_id: Option<CieId>,
15 impl<'tcx> UnwindContext<'tcx> {
20 let mut frame_table = FrameTable::default();
23 let cie_id = if let Some(cie) = isa.create_systemv_cie() {
24 Some(frame_table.add_cie(cie))
36 pub(crate) fn add_function(&mut self, func_id: FuncId, context: &Context, isa: &dyn TargetIsa) {
37 let unwind_info = if let Some(unwind_info) = context.create_unwind_info(isa).unwrap() {
44 UnwindInfo::SystemV(unwind_info) => {
45 self.frame_table.add_fde(self.cie_id.unwrap(), unwind_info.to_fde(Address::Symbol {
46 symbol: func_id.as_u32() as usize,
50 UnwindInfo::WindowsX64(_) => {
51 // FIXME implement this
56 pub(crate) fn emit<P: WriteDebugInfo>(self, product: &mut P) {
57 let mut eh_frame = EhFrame::from(super::emit::WriterRelocate::new(super::target_endian(self.tcx)));
58 self.frame_table.write_eh_frame(&mut eh_frame).unwrap();
60 if !eh_frame.0.writer.slice().is_empty() {
61 let id = eh_frame.id();
62 let section_id = product.add_debug_section(id, eh_frame.0.writer.into_vec());
63 let mut section_map = FxHashMap::default();
64 section_map.insert(id, section_id);
66 for reloc in &eh_frame.0.relocs {
67 product.add_debug_reloc(§ion_map, §ion_id, reloc);
72 pub(crate) unsafe fn register_jit(
74 jit_module: &mut Module<cranelift_simplejit::SimpleJITBackend>,
75 ) -> Option<UnwindRegistry> {
76 let mut eh_frame = EhFrame::from(super::emit::WriterRelocate::new(super::target_endian(self.tcx)));
77 self.frame_table.write_eh_frame(&mut eh_frame).unwrap();
79 if eh_frame.0.writer.slice().is_empty() {
83 let mut eh_frame = eh_frame.0.relocate_for_jit(jit_module);
85 // GCC expects a terminating "empty" length, so write a 0 length at the end of the table.
86 eh_frame.extend(&[0, 0, 0, 0]);
88 let mut registrations = Vec::new();
90 // =======================================================================
91 // Everything after this line up to the end of the file is loosly based on
92 // https://github.com/bytecodealliance/wasmtime/blob/4471a82b0c540ff48960eca6757ccce5b1b5c3e4/crates/jit/src/unwind/systemv.rs
94 if #[cfg(target_os = "macos")] {
95 // On macOS, `__register_frame` takes a pointer to a single FDE
96 let start = eh_frame.as_ptr();
97 let end = start.add(eh_frame.len());
98 let mut current = start;
100 // Walk all of the entries in the frame table and register them
101 while current < end {
102 let len = std::ptr::read::<u32>(current as *const u32) as usize;
105 if current != start {
106 __register_frame(current);
107 registrations.push(current as usize);
110 // Move to the next table entry (+4 because the length itself is not inclusive)
111 current = current.add(len + 4);
114 // On other platforms, `__register_frame` will walk the FDEs until an entry of length 0
115 let ptr = eh_frame.as_ptr();
116 __register_frame(ptr);
117 registrations.push(ptr as usize);
121 Some(UnwindRegistry {
122 _frame_table: eh_frame,
128 /// Represents a registry of function unwind information for System V ABI.
129 pub(crate) struct UnwindRegistry {
130 _frame_table: Vec<u8>,
131 registrations: Vec<usize>,
136 fn __register_frame(fde: *const u8);
137 fn __deregister_frame(fde: *const u8);
140 impl Drop for UnwindRegistry {
143 // libgcc stores the frame entries as a linked list in decreasing sort order
144 // based on the PC value of the registered entry.
146 // As we store the registrations in increasing order, it would be O(N^2) to
147 // deregister in that order.
149 // To ensure that we just pop off the first element in the list upon every
150 // deregistration, walk our list of registrations backwards.
151 for fde in self.registrations.iter().rev() {
152 __deregister_frame(*fde as *const _);