compiler/rustc_codegen_cranelift/src/debuginfo/unwind.rs

   1 //! Unwind info generation (`.eh_frame`)
   2
   3 use crate::prelude::*;
   4
   5 use cranelift_codegen::isa::{unwind::UnwindInfo, TargetIsa};
   6
   7 use cranelift_object::ObjectProduct;
   8 use gimli::write::{Address, CieId, EhFrame, FrameTable, Section};
   9 use gimli::RunTimeEndian;
  10
  11 use super::object::WriteDebugInfo;
  12
  13 pub(crate) struct UnwindContext {
  14     endian: RunTimeEndian,
  15     frame_table: FrameTable,
  16     cie_id: Option<CieId>,
  17 }
  18
  19 impl UnwindContext {
  20     pub(crate) fn new(tcx: TyCtxt<'_>, isa: &dyn TargetIsa, pic_eh_frame: bool) -> Self {
  21         let endian = super::target_endian(tcx);
  22         let mut frame_table = FrameTable::default();
  23
  24         let cie_id = if let Some(mut cie) = isa.create_systemv_cie() {
  25             if pic_eh_frame {
  26                 cie.fde_address_encoding =
  27                     gimli::DwEhPe(gimli::DW_EH_PE_pcrel.0 | gimli::DW_EH_PE_sdata4.0);
  28             }
  29             Some(frame_table.add_cie(cie))
  30         } else {
  31             None
  32         };
  33
  34         UnwindContext { endian, frame_table, cie_id }
  35     }
  36
  37     pub(crate) fn add_function(&mut self, func_id: FuncId, context: &Context, isa: &dyn TargetIsa) {
  38         let unwind_info = if let Some(unwind_info) = context.create_unwind_info(isa).unwrap() {
  39             unwind_info
  40         } else {
  41             return;
  42         };
  43
  44         match unwind_info {
  45             UnwindInfo::SystemV(unwind_info) => {
  46                 self.frame_table.add_fde(
  47                     self.cie_id.unwrap(),
  48                     unwind_info
  49                         .to_fde(Address::Symbol { symbol: func_id.as_u32() as usize, addend: 0 }),
  50                 );
  51             }
  52             UnwindInfo::WindowsX64(_) => {
  53                 // FIXME implement this
  54             }
  55             unwind_info => unimplemented!("{:?}", unwind_info),
  56         }
  57     }
  58
  59     pub(crate) fn emit(self, product: &mut ObjectProduct) {
  60         let mut eh_frame = EhFrame::from(super::emit::WriterRelocate::new(self.endian));
  61         self.frame_table.write_eh_frame(&mut eh_frame).unwrap();
  62
  63         if !eh_frame.0.writer.slice().is_empty() {
  64             let id = eh_frame.id();
  65             let section_id = product.add_debug_section(id, eh_frame.0.writer.into_vec());
  66             let mut section_map = FxHashMap::default();
  67             section_map.insert(id, section_id);
  68
  69             for reloc in &eh_frame.0.relocs {
  70                 product.add_debug_reloc(&section_map, &section_id, reloc);
  71             }
  72         }
  73     }
  74
  75     #[cfg(all(feature = "jit", windows))]
  76     pub(crate) unsafe fn register_jit(self, _jit_module: &cranelift_jit::JITModule) {}
  77
  78     #[cfg(all(feature = "jit", not(windows)))]
  79     pub(crate) unsafe fn register_jit(self, jit_module: &cranelift_jit::JITModule) {
  80         let mut eh_frame = EhFrame::from(super::emit::WriterRelocate::new(self.endian));
  81         self.frame_table.write_eh_frame(&mut eh_frame).unwrap();
  82
  83         if eh_frame.0.writer.slice().is_empty() {
  84             return;
  85         }
  86
  87         let mut eh_frame = eh_frame.0.relocate_for_jit(jit_module);
  88
  89         // GCC expects a terminating "empty" length, so write a 0 length at the end of the table.
  90         eh_frame.extend(&[0, 0, 0, 0]);
  91
  92         // FIXME support unregistering unwind tables once cranelift-jit supports deallocating
  93         // individual functions
  94         #[allow(unused_variables)]
  95         let (eh_frame, eh_frame_len, _) = Vec::into_raw_parts(eh_frame);
  96
  97         // =======================================================================
  98         // Everything after this line up to the end of the file is loosly based on
  99         // https://github.com/bytecodealliance/wasmtime/blob/4471a82b0c540ff48960eca6757ccce5b1b5c3e4/crates/jit/src/unwind/systemv.rs
 100         #[cfg(target_os = "macos")]
 101         {
 102             // On macOS, `__register_frame` takes a pointer to a single FDE
 103             let start = eh_frame;
 104             let end = start.add(eh_frame_len);
 105             let mut current = start;
 106
 107             // Walk all of the entries in the frame table and register them
 108             while current < end {
 109                 let len = std::ptr::read::<u32>(current as *const u32) as usize;
 110
 111                 // Skip over the CIE
 112                 if current != start {
 113                     __register_frame(current);
 114                 }
 115
 116                 // Move to the next table entry (+4 because the length itself is not inclusive)
 117                 current = current.add(len + 4);
 118             }
 119         }
 120         #[cfg(not(target_os = "macos"))]
 121         {
 122             // On other platforms, `__register_frame` will walk the FDEs until an entry of length 0
 123             __register_frame(eh_frame);
 124         }
 125     }
 126 }
 127
 128 extern "C" {
 129     // libunwind import
 130     fn __register_frame(fde: *const u8);
 131 }