src/backend.rs

   1 //! Abstraction around the object writing crate
   2
   3 use std::convert::{TryFrom, TryInto};
   4
   5 use rustc_data_structures::fx::FxHashMap;
   6 use rustc_session::Session;
   7
   8 use cranelift_codegen::isa::TargetIsa;
   9 use cranelift_module::FuncId;
  10 use cranelift_object::{ObjectBuilder, ObjectModule, ObjectProduct};
  11
  12 use object::write::{Relocation, StandardSegment};
  13 use object::{RelocationEncoding, SectionKind};
  14
  15 use gimli::SectionId;
  16
  17 use crate::debuginfo::{DebugReloc, DebugRelocName};
  18
  19 pub(crate) trait WriteDebugInfo {
  20     type SectionId: Copy;
  21
  22     fn add_debug_section(&mut self, name: SectionId, data: Vec<u8>) -> Self::SectionId;
  23     fn add_debug_reloc(
  24         &mut self,
  25         section_map: &FxHashMap<SectionId, Self::SectionId>,
  26         from: &Self::SectionId,
  27         reloc: &DebugReloc,
  28     );
  29 }
  30
  31 impl WriteDebugInfo for ObjectProduct {
  32     type SectionId = (object::write::SectionId, object::write::SymbolId);
  33
  34     fn add_debug_section(
  35         &mut self,
  36         id: SectionId,
  37         data: Vec<u8>,
  38     ) -> (object::write::SectionId, object::write::SymbolId) {
  39         let name = if self.object.format() == object::BinaryFormat::MachO {
  40             id.name().replace('.', "__") // machO expects __debug_info instead of .debug_info
  41         } else {
  42             id.name().to_string()
  43         }
  44         .into_bytes();
  45
  46         let segment = self.object.segment_name(StandardSegment::Debug).to_vec();
  47         // FIXME use SHT_X86_64_UNWIND for .eh_frame
  48         let section_id = self.object.add_section(
  49             segment,
  50             name,
  51             if id == SectionId::EhFrame { SectionKind::ReadOnlyData } else { SectionKind::Debug },
  52         );
  53         self.object
  54             .section_mut(section_id)
  55             .set_data(data, if id == SectionId::EhFrame { 8 } else { 1 });
  56         let symbol_id = self.object.section_symbol(section_id);
  57         (section_id, symbol_id)
  58     }
  59
  60     fn add_debug_reloc(
  61         &mut self,
  62         section_map: &FxHashMap<SectionId, Self::SectionId>,
  63         from: &Self::SectionId,
  64         reloc: &DebugReloc,
  65     ) {
  66         let (symbol, symbol_offset) = match reloc.name {
  67             DebugRelocName::Section(id) => (section_map.get(&id).unwrap().1, 0),
  68             DebugRelocName::Symbol(id) => {
  69                 let symbol_id = self.function_symbol(FuncId::from_u32(id.try_into().unwrap()));
  70                 self.object
  71                     .symbol_section_and_offset(symbol_id)
  72                     .expect("Debug reloc for undef sym???")
  73             }
  74         };
  75         self.object
  76             .add_relocation(
  77                 from.0,
  78                 Relocation {
  79                     offset: u64::from(reloc.offset),
  80                     symbol,
  81                     kind: reloc.kind,
  82                     encoding: RelocationEncoding::Generic,
  83                     size: reloc.size * 8,
  84                     addend: i64::try_from(symbol_offset).unwrap() + reloc.addend,
  85                 },
  86             )
  87             .unwrap();
  88     }
  89 }
  90
  91 pub(crate) fn make_module(sess: &Session, isa: Box<dyn TargetIsa>, name: String) -> ObjectModule {
  92     let mut builder =
  93         ObjectBuilder::new(isa, name + ".o", cranelift_module::default_libcall_names()).unwrap();
  94     // Unlike cg_llvm, cg_clif defaults to disabling -Zfunction-sections. For cg_llvm binary size
  95     // is important, while cg_clif cares more about compilation times. Enabling -Zfunction-sections
  96     // can easily double the amount of time necessary to perform linking.
  97     builder.per_function_section(sess.opts.debugging_opts.function_sections.unwrap_or(false));
  98     ObjectModule::new(builder)
  99 }