src/backend.rs

   1 use std::convert::{TryFrom, TryInto};
   2
   3 use rustc_data_structures::fx::FxHashMap;
   4 use rustc_session::Session;
   5
   6 use cranelift_module::{FuncId, Module};
   7
   8 use object::write::*;
   9 use object::{RelocationEncoding, RelocationKind, SectionKind, SymbolFlags};
  10
  11 use cranelift_object::{ObjectBackend, ObjectBuilder, ObjectProduct};
  12
  13 use gimli::SectionId;
  14
  15 use crate::debuginfo::{DebugReloc, DebugRelocName};
  16
  17 pub(crate) trait WriteMetadata {
  18     fn add_rustc_section(&mut self, symbol_name: String, data: Vec<u8>, is_like_osx: bool);
  19 }
  20
  21 impl WriteMetadata for object::write::Object {
  22     fn add_rustc_section(&mut self, symbol_name: String, data: Vec<u8>, _is_like_osx: bool) {
  23         let segment = self
  24             .segment_name(object::write::StandardSegment::Data)
  25             .to_vec();
  26         let section_id = self.add_section(segment, b".rustc".to_vec(), object::SectionKind::Data);
  27         let offset = self.append_section_data(section_id, &data, 1);
  28         // For MachO and probably PE this is necessary to prevent the linker from throwing away the
  29         // .rustc section. For ELF this isn't necessary, but it also doesn't harm.
  30         self.add_symbol(object::write::Symbol {
  31             name: symbol_name.into_bytes(),
  32             value: offset,
  33             size: data.len() as u64,
  34             kind: object::SymbolKind::Data,
  35             scope: object::SymbolScope::Dynamic,
  36             weak: false,
  37             section: SymbolSection::Section(section_id),
  38             flags: SymbolFlags::None,
  39         });
  40     }
  41 }
  42
  43 pub(crate) trait WriteDebugInfo {
  44     type SectionId: Copy;
  45
  46     fn add_debug_section(&mut self, name: SectionId, data: Vec<u8>) -> Self::SectionId;
  47     fn add_debug_reloc(
  48         &mut self,
  49         section_map: &FxHashMap<SectionId, Self::SectionId>,
  50         from: &Self::SectionId,
  51         reloc: &DebugReloc,
  52     );
  53 }
  54
  55 impl WriteDebugInfo for ObjectProduct {
  56     type SectionId = (object::write::SectionId, object::write::SymbolId);
  57
  58     fn add_debug_section(
  59         &mut self,
  60         id: SectionId,
  61         data: Vec<u8>,
  62     ) -> (object::write::SectionId, object::write::SymbolId) {
  63         let name = if self.object.format() == object::BinaryFormat::MachO {
  64             id.name().replace('.', "__") // machO expects __debug_info instead of .debug_info
  65         } else {
  66             id.name().to_string()
  67         }
  68         .into_bytes();
  69
  70         let segment = self.object.segment_name(StandardSegment::Debug).to_vec();
  71         // FIXME use SHT_X86_64_UNWIND for .eh_frame
  72         let section_id = self.object.add_section(segment, name.clone(), if id == SectionId::EhFrame {
  73             SectionKind::ReadOnlyData
  74         } else {
  75             SectionKind::Debug
  76         });
  77         self.object.section_mut(section_id).set_data(data, if id == SectionId::EhFrame {
  78             8
  79         } else {
  80             1
  81         });
  82         let symbol_id = self.object.section_symbol(section_id);
  83         (section_id, symbol_id)
  84     }
  85
  86     fn add_debug_reloc(
  87         &mut self,
  88         section_map: &FxHashMap<SectionId, Self::SectionId>,
  89         from: &Self::SectionId,
  90         reloc: &DebugReloc,
  91     ) {
  92         let (symbol, symbol_offset) = match reloc.name {
  93             DebugRelocName::Section(id) => (section_map.get(&id).unwrap().1, 0),
  94             DebugRelocName::Symbol(id) => {
  95                 let symbol_id = self.function_symbol(FuncId::from_u32(id.try_into().unwrap()));
  96                 self.object
  97                     .symbol_section_and_offset(symbol_id)
  98                     .expect("Debug reloc for undef sym???")
  99             }
 100         };
 101         self.object
 102             .add_relocation(
 103                 from.0,
 104                 Relocation {
 105                     offset: u64::from(reloc.offset),
 106                     symbol,
 107                     kind: reloc.kind,
 108                     encoding: RelocationEncoding::Generic,
 109                     size: reloc.size * 8,
 110                     addend: i64::try_from(symbol_offset).unwrap() + reloc.addend,
 111                 },
 112             )
 113             .unwrap();
 114     }
 115 }
 116
 117 // FIXME remove once atomic instructions are implemented in Cranelift.
 118 pub(crate) trait AddConstructor {
 119     fn add_constructor(&mut self, func_id: FuncId);
 120 }
 121
 122 impl AddConstructor for ObjectProduct {
 123     fn add_constructor(&mut self, func_id: FuncId) {
 124         let symbol = self.function_symbol(func_id);
 125         let segment = self
 126             .object
 127             .segment_name(object::write::StandardSegment::Data);
 128         let init_array_section =
 129             self.object
 130                 .add_section(segment.to_vec(), b".init_array".to_vec(), SectionKind::Data);
 131         self.object.append_section_data(
 132             init_array_section,
 133             &std::iter::repeat(0)
 134                 .take(8 /*FIXME pointer size*/)
 135                 .collect::<Vec<u8>>(),
 136             8,
 137         );
 138         self.object
 139             .add_relocation(
 140                 init_array_section,
 141                 object::write::Relocation {
 142                     offset: 0,
 143                     size: 64, // FIXME pointer size
 144                     kind: RelocationKind::Absolute,
 145                     encoding: RelocationEncoding::Generic,
 146                     symbol,
 147                     addend: 0,
 148                 },
 149             )
 150             .unwrap();
 151     }
 152 }
 153
 154 pub(crate) trait Emit {
 155     fn emit(self) -> Vec<u8>;
 156 }
 157
 158 impl Emit for ObjectProduct {
 159     fn emit(self) -> Vec<u8> {
 160         self.object.write().unwrap()
 161     }
 162 }
 163
 164 pub(crate) fn with_object(sess: &Session, name: &str, f: impl FnOnce(&mut Object)) -> Vec<u8> {
 165     let triple = crate::build_isa(sess, true).triple().clone();
 166
 167     let binary_format = match triple.binary_format {
 168         target_lexicon::BinaryFormat::Elf => object::BinaryFormat::Elf,
 169         target_lexicon::BinaryFormat::Coff => object::BinaryFormat::Coff,
 170         target_lexicon::BinaryFormat::Macho => object::BinaryFormat::MachO,
 171         binary_format => sess.fatal(&format!("binary format {} is unsupported", binary_format)),
 172     };
 173     let architecture = match triple.architecture {
 174         target_lexicon::Architecture::X86_32(_) => object::Architecture::I386,
 175         target_lexicon::Architecture::X86_64 => object::Architecture::X86_64,
 176         target_lexicon::Architecture::Arm(_) => object::Architecture::Arm,
 177         target_lexicon::Architecture::Aarch64(_) => object::Architecture::Aarch64,
 178         architecture => sess.fatal(&format!(
 179             "target architecture {:?} is unsupported",
 180             architecture,
 181         )),
 182     };
 183     let endian = match triple.endianness().unwrap() {
 184         target_lexicon::Endianness::Little => object::Endianness::Little,
 185         target_lexicon::Endianness::Big => object::Endianness::Big,
 186     };
 187
 188     let mut metadata_object = object::write::Object::new(binary_format, architecture, endian);
 189     metadata_object.add_file_symbol(name.as_bytes().to_vec());
 190     f(&mut metadata_object);
 191     metadata_object.write().unwrap()
 192 }
 193
 194 pub(crate) type Backend =
 195     impl cranelift_module::Backend<Product: AddConstructor + Emit + WriteDebugInfo>;
 196
 197 pub(crate) fn make_module(sess: &Session, name: String) -> Module<Backend> {
 198     let mut builder = ObjectBuilder::new(
 199         crate::build_isa(sess, true),
 200         name + ".o",
 201         cranelift_module::default_libcall_names(),
 202     )
 203     .unwrap();
 204     if std::env::var("CG_CLIF_FUNCTION_SECTIONS").is_ok() {
 205         builder.per_function_section(true);
 206     }
 207     let module: Module<ObjectBackend> = Module::new(
 208         builder,
 209     );
 210     module
 211 }