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//! Abstraction around the object writing crate
use std::convert::{TryFrom, TryInto};
use rustc_data_structures::fx::FxHashMap;
use rustc_session::Session;
use cranelift_module::FuncId;
use object::write::*;
use object::{RelocationEncoding, SectionKind, SymbolFlags};
use cranelift_object::{ObjectBuilder, ObjectModule, ObjectProduct};
use gimli::SectionId;
use crate::debuginfo::{DebugReloc, DebugRelocName};
pub(crate) trait WriteMetadata {
fn add_rustc_section(&mut self, symbol_name: String, data: Vec<u8>, is_like_osx: bool);
}
impl WriteMetadata for object::write::Object {
fn add_rustc_section(&mut self, symbol_name: String, data: Vec<u8>, _is_like_osx: bool) {
let segment = self.segment_name(object::write::StandardSegment::Data).to_vec();
let section_id = self.add_section(segment, b".rustc".to_vec(), object::SectionKind::Data);
let offset = self.append_section_data(section_id, &data, 1);
// For MachO and probably PE this is necessary to prevent the linker from throwing away the
// .rustc section. For ELF this isn't necessary, but it also doesn't harm.
self.add_symbol(object::write::Symbol {
name: symbol_name.into_bytes(),
value: offset,
size: data.len() as u64,
kind: object::SymbolKind::Data,
scope: object::SymbolScope::Dynamic,
weak: false,
section: SymbolSection::Section(section_id),
flags: SymbolFlags::None,
});
}
}
pub(crate) trait WriteDebugInfo {
type SectionId: Copy;
fn add_debug_section(&mut self, name: SectionId, data: Vec<u8>) -> Self::SectionId;
fn add_debug_reloc(
&mut self,
section_map: &FxHashMap<SectionId, Self::SectionId>,
from: &Self::SectionId,
reloc: &DebugReloc,
);
}
impl WriteDebugInfo for ObjectProduct {
type SectionId = (object::write::SectionId, object::write::SymbolId);
fn add_debug_section(
&mut self,
id: SectionId,
data: Vec<u8>,
) -> (object::write::SectionId, object::write::SymbolId) {
let name = if self.object.format() == object::BinaryFormat::MachO {
id.name().replace('.', "__") // machO expects __debug_info instead of .debug_info
} else {
id.name().to_string()
}
.into_bytes();
let segment = self.object.segment_name(StandardSegment::Debug).to_vec();
// FIXME use SHT_X86_64_UNWIND for .eh_frame
let section_id = self.object.add_section(
segment,
name,
if id == SectionId::EhFrame { SectionKind::ReadOnlyData } else { SectionKind::Debug },
);
self.object
.section_mut(section_id)
.set_data(data, if id == SectionId::EhFrame { 8 } else { 1 });
let symbol_id = self.object.section_symbol(section_id);
(section_id, symbol_id)
}
fn add_debug_reloc(
&mut self,
section_map: &FxHashMap<SectionId, Self::SectionId>,
from: &Self::SectionId,
reloc: &DebugReloc,
) {
let (symbol, symbol_offset) = match reloc.name {
DebugRelocName::Section(id) => (section_map.get(&id).unwrap().1, 0),
DebugRelocName::Symbol(id) => {
let symbol_id = self.function_symbol(FuncId::from_u32(id.try_into().unwrap()));
self.object
.symbol_section_and_offset(symbol_id)
.expect("Debug reloc for undef sym???")
}
};
self.object
.add_relocation(
from.0,
Relocation {
offset: u64::from(reloc.offset),
symbol,
kind: reloc.kind,
encoding: RelocationEncoding::Generic,
size: reloc.size * 8,
addend: i64::try_from(symbol_offset).unwrap() + reloc.addend,
},
)
.unwrap();
}
}
pub(crate) fn with_object(sess: &Session, name: &str, f: impl FnOnce(&mut Object)) -> Vec<u8> {
let triple = crate::build_isa(sess).triple().clone();
let binary_format = match triple.binary_format {
target_lexicon::BinaryFormat::Elf => object::BinaryFormat::Elf,
target_lexicon::BinaryFormat::Coff => object::BinaryFormat::Coff,
target_lexicon::BinaryFormat::Macho => object::BinaryFormat::MachO,
binary_format => sess.fatal(&format!("binary format {} is unsupported", binary_format)),
};
let architecture = match triple.architecture {
target_lexicon::Architecture::X86_32(_) => object::Architecture::I386,
target_lexicon::Architecture::X86_64 => object::Architecture::X86_64,
target_lexicon::Architecture::Arm(_) => object::Architecture::Arm,
target_lexicon::Architecture::Aarch64(_) => object::Architecture::Aarch64,
architecture => {
sess.fatal(&format!("target architecture {:?} is unsupported", architecture,))
}
};
let endian = match triple.endianness().unwrap() {
target_lexicon::Endianness::Little => object::Endianness::Little,
target_lexicon::Endianness::Big => object::Endianness::Big,
};
let mut metadata_object = object::write::Object::new(binary_format, architecture, endian);
metadata_object.add_file_symbol(name.as_bytes().to_vec());
f(&mut metadata_object);
metadata_object.write().unwrap()
}
pub(crate) fn make_module(sess: &Session, name: String) -> ObjectModule {
let mut builder = ObjectBuilder::new(
crate::build_isa(sess),
name + ".o",
cranelift_module::default_libcall_names(),
)
.unwrap();
// Unlike cg_llvm, cg_clif defaults to disabling -Zfunction-sections. For cg_llvm binary size
// is important, while cg_clif cares more about compilation times. Enabling -Zfunction-sections
// can easily double the amount of time necessary to perform linking.
builder.per_function_section(sess.opts.debugging_opts.function_sections.unwrap_or(false));
ObjectModule::new(builder)
}
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