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_module::FuncId;
   9
  10 use object::write::*;
  11 use object::{RelocationEncoding, SectionKind, SymbolFlags};
  12
  13 use cranelift_object::{ObjectBuilder, ObjectModule, ObjectProduct};
  14
  15 use gimli::SectionId;
  16
  17 use crate::debuginfo::{DebugReloc, DebugRelocName};
  18
  19 pub(crate) trait WriteMetadata {
  20     fn add_rustc_section(&mut self, symbol_name: String, data: Vec<u8>, is_like_osx: bool);
  21 }
  22
  23 impl WriteMetadata for object::write::Object {
  24     fn add_rustc_section(&mut self, symbol_name: String, data: Vec<u8>, _is_like_osx: bool) {
  25         let segment = self
  26             .segment_name(object::write::StandardSegment::Data)
  27             .to_vec();
  28         let section_id = self.add_section(segment, b".rustc".to_vec(), object::SectionKind::Data);
  29         let offset = self.append_section_data(section_id, &data, 1);
  30         // For MachO and probably PE this is necessary to prevent the linker from throwing away the
  31         // .rustc section. For ELF this isn't necessary, but it also doesn't harm.
  32         self.add_symbol(object::write::Symbol {
  33             name: symbol_name.into_bytes(),
  34             value: offset,
  35             size: data.len() as u64,
  36             kind: object::SymbolKind::Data,
  37             scope: object::SymbolScope::Dynamic,
  38             weak: false,
  39             section: SymbolSection::Section(section_id),
  40             flags: SymbolFlags::None,
  41         });
  42     }
  43 }
  44
  45 pub(crate) trait WriteDebugInfo {
  46     type SectionId: Copy;
  47
  48     fn add_debug_section(&mut self, name: SectionId, data: Vec<u8>) -> Self::SectionId;
  49     fn add_debug_reloc(
  50         &mut self,
  51         section_map: &FxHashMap<SectionId, Self::SectionId>,
  52         from: &Self::SectionId,
  53         reloc: &DebugReloc,
  54     );
  55 }
  56
  57 impl WriteDebugInfo for ObjectProduct {
  58     type SectionId = (object::write::SectionId, object::write::SymbolId);
  59
  60     fn add_debug_section(
  61         &mut self,
  62         id: SectionId,
  63         data: Vec<u8>,
  64     ) -> (object::write::SectionId, object::write::SymbolId) {
  65         let name = if self.object.format() == object::BinaryFormat::MachO {
  66             id.name().replace('.', "__") // machO expects __debug_info instead of .debug_info
  67         } else {
  68             id.name().to_string()
  69         }
  70         .into_bytes();
  71
  72         let segment = self.object.segment_name(StandardSegment::Debug).to_vec();
  73         // FIXME use SHT_X86_64_UNWIND for .eh_frame
  74         let section_id = self.object.add_section(
  75             segment,
  76             name,
  77             if id == SectionId::EhFrame {
  78                 SectionKind::ReadOnlyData
  79             } else {
  80                 SectionKind::Debug
  81             },
  82         );
  83         self.object
  84             .section_mut(section_id)
  85             .set_data(data, if id == SectionId::EhFrame { 8 } else { 1 });
  86         let symbol_id = self.object.section_symbol(section_id);
  87         (section_id, symbol_id)
  88     }
  89
  90     fn add_debug_reloc(
  91         &mut self,
  92         section_map: &FxHashMap<SectionId, Self::SectionId>,
  93         from: &Self::SectionId,
  94         reloc: &DebugReloc,
  95     ) {
  96         let (symbol, symbol_offset) = match reloc.name {
  97             DebugRelocName::Section(id) => (section_map.get(&id).unwrap().1, 0),
  98             DebugRelocName::Symbol(id) => {
  99                 let symbol_id = self.function_symbol(FuncId::from_u32(id.try_into().unwrap()));
 100                 self.object
 101                     .symbol_section_and_offset(symbol_id)
 102                     .expect("Debug reloc for undef sym???")
 103             }
 104         };
 105         self.object
 106             .add_relocation(
 107                 from.0,
 108                 Relocation {
 109                     offset: u64::from(reloc.offset),
 110                     symbol,
 111                     kind: reloc.kind,
 112                     encoding: RelocationEncoding::Generic,
 113                     size: reloc.size * 8,
 114                     addend: i64::try_from(symbol_offset).unwrap() + reloc.addend,
 115                 },
 116             )
 117             .unwrap();
 118     }
 119 }
 120
 121 pub(crate) fn with_object(sess: &Session, name: &str, f: impl FnOnce(&mut Object)) -> Vec<u8> {
 122     let triple = crate::build_isa(sess).triple().clone();
 123
 124     let binary_format = match triple.binary_format {
 125         target_lexicon::BinaryFormat::Elf => object::BinaryFormat::Elf,
 126         target_lexicon::BinaryFormat::Coff => object::BinaryFormat::Coff,
 127         target_lexicon::BinaryFormat::Macho => object::BinaryFormat::MachO,
 128         binary_format => sess.fatal(&format!("binary format {} is unsupported", binary_format)),
 129     };
 130     let architecture = match triple.architecture {
 131         target_lexicon::Architecture::X86_32(_) => object::Architecture::I386,
 132         target_lexicon::Architecture::X86_64 => object::Architecture::X86_64,
 133         target_lexicon::Architecture::Arm(_) => object::Architecture::Arm,
 134         target_lexicon::Architecture::Aarch64(_) => object::Architecture::Aarch64,
 135         architecture => sess.fatal(&format!(
 136             "target architecture {:?} is unsupported",
 137             architecture,
 138         )),
 139     };
 140     let endian = match triple.endianness().unwrap() {
 141         target_lexicon::Endianness::Little => object::Endianness::Little,
 142         target_lexicon::Endianness::Big => object::Endianness::Big,
 143     };
 144
 145     let mut metadata_object = object::write::Object::new(binary_format, architecture, endian);
 146     metadata_object.add_file_symbol(name.as_bytes().to_vec());
 147     f(&mut metadata_object);
 148     metadata_object.write().unwrap()
 149 }
 150
 151 pub(crate) fn make_module(sess: &Session, name: String) -> ObjectModule {
 152     let mut builder = ObjectBuilder::new(
 153         crate::build_isa(sess),
 154         name + ".o",
 155         cranelift_module::default_libcall_names(),
 156     )
 157     .unwrap();
 158     // Unlike cg_llvm, cg_clif defaults to disabling -Zfunction-sections. For cg_llvm binary size
 159     // is important, while cg_clif cares more about compilation times. Enabling -Zfunction-sections
 160     // can easily double the amount of time necessary to perform linking.
 161     builder.per_function_section(sess.opts.debugging_opts.function_sections.unwrap_or(false));
 162     ObjectModule::new(builder)
 163 }