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Auto merge of #83640 - bjorn3:shared_metadata_reader, r=nagisa

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Use the object crate for metadata reading

This allows sharing the metadata reader between cg_llvm, cg_clif and other codegen backends.

This is not currently useful for rlib reading with cg_spirv ([rust-gpu](https://github.com/EmbarkStudios/rust-gpu/)) as it uses tar rather than ar as .rlib format, but it is useful for dylib reading required for loading proc macros. (cc `@eddyb)`

The object crate is already trusted as dependency of libstd through backtrace. As far as I know it supports reading all object file formats used by targets for which we support rust dylibs with crate metadata, but I am not certain. If this happens to not be the case, I could keep using LLVM for reading dylib metadata.

Marked as WIP for a perf run and as it is based on #83637.
This commit is contained in:
bors 2021-05-14 12:58:58 +00:00
commit 75da570d78
10 changed files with 98 additions and 195 deletions
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18
compiler/rustc_codegen_llvm/src/base.rs
View file

@ -18,7 +18,6 @@ use crate::builder::Builder;
use crate::common;
use crate::context::CodegenCx;
use crate::llvm;
use crate::metadata;
use crate::value::Value;
use rustc_codegen_ssa::base::maybe_create_entry_wrapper;
@ -47,6 +46,22 @@ pub fn write_compressed_metadata<'tcx>(
use snap::write::FrameEncoder;
use std::io::Write;
// Historical note:
//
// When using link.exe it was seen that the section name `.note.rustc`
// was getting shortened to `.note.ru`, and according to the PE and COFF
// specification:
//
// > Executable images do not use a string table and do not support
// > section names longer than 8 characters
//
// https://docs.microsoft.com/en-us/windows/win32/debug/pe-format
//
// As a result, we choose a slightly shorter name! As to why
// `.note.rustc` works on MinGW, see
// https://github.com/llvm/llvm-project/blob/llvmorg-12.0.0/lld/COFF/Writer.cpp#L1190-L1197
let section_name = if tcx.sess.target.is_like_osx { "__DATA,.rustc" } else { ".rustc" };
let (metadata_llcx, metadata_llmod) = (&*llvm_module.llcx, llvm_module.llmod());
let mut compressed = tcx.metadata_encoding_version();
FrameEncoder::new(&mut compressed).write_all(&metadata.raw_data).unwrap();
@ -59,7 +74,6 @@ pub fn write_compressed_metadata<'tcx>(
unsafe { llvm::LLVMAddGlobal(metadata_llmod, common::val_ty(llconst), buf.as_ptr()) };
unsafe {
llvm::LLVMSetInitializer(llglobal, llconst);
let section_name = metadata::metadata_section_name(&tcx.sess.target);
let name = SmallCStr::new(section_name);
llvm::LLVMSetSection(llglobal, name.as_ptr());

3
compiler/rustc_codegen_llvm/src/lib.rs
View file

@ -69,7 +69,6 @@ pub mod llvm {
}
mod llvm_util;
mod metadata;
mod mono_item;
mod type_;
mod type_of;
@ -251,7 +250,7 @@ impl CodegenBackend for LlvmCodegenBackend {
}
fn metadata_loader(&self) -> Box<MetadataLoaderDyn> {
Box::new(metadata::LlvmMetadataLoader)
Box::new(rustc_codegen_ssa::back::metadata::DefaultMetadataLoader)
}
fn provide(&self, _providers: &mut ty::query::Providers) {}

112
compiler/rustc_codegen_llvm/src/metadata.rs
View file

@ -1,112 +0,0 @@
use crate::llvm;
use crate::llvm::archive_ro::ArchiveRO;
use crate::llvm::{mk_section_iter, False, ObjectFile};
use rustc_middle::middle::cstore::MetadataLoader;
use rustc_target::spec::Target;
use rustc_codegen_ssa::METADATA_FILENAME;
use rustc_data_structures::owning_ref::OwningRef;
use rustc_data_structures::rustc_erase_owner;
use tracing::debug;
use rustc_fs_util::path_to_c_string;
use std::path::Path;
use std::slice;
pub use rustc_data_structures::sync::MetadataRef;
pub struct LlvmMetadataLoader;
impl MetadataLoader for LlvmMetadataLoader {
fn get_rlib_metadata(&self, _: &Target, filename: &Path) -> Result<MetadataRef, String> {
// Use ArchiveRO for speed here, it's backed by LLVM and uses mmap
// internally to read the file. We also avoid even using a memcpy by
// just keeping the archive along while the metadata is in use.
let archive =
ArchiveRO::open(filename).map(|ar| OwningRef::new(Box::new(ar))).map_err(|e| {
debug!("llvm didn't like `{}`: {}", filename.display(), e);
format!("failed to read rlib metadata in '{}': {}", filename.display(), e)
})?;
let buf: OwningRef<_, [u8]> = archive.try_map(|ar| {
ar.iter()
.filter_map(|s| s.ok())
.find(|sect| sect.name() == Some(METADATA_FILENAME))
.map(|s| s.data())
.ok_or_else(|| {
debug!("didn't find '{}' in the archive", METADATA_FILENAME);
format!("failed to read rlib metadata: '{}'", filename.display())
})
})?;
Ok(rustc_erase_owner!(buf))
}
fn get_dylib_metadata(&self, target: &Target, filename: &Path) -> Result<MetadataRef, String> {
unsafe {
let buf = path_to_c_string(filename);
let mb = llvm::LLVMRustCreateMemoryBufferWithContentsOfFile(buf.as_ptr())
.ok_or_else(|| format!("error reading library: '{}'", filename.display()))?;
let of =
ObjectFile::new(mb).map(|of| OwningRef::new(Box::new(of))).ok_or_else(|| {
format!("provided path not an object file: '{}'", filename.display())
})?;
let buf = of.try_map(|of| search_meta_section(of, target, filename))?;
Ok(rustc_erase_owner!(buf))
}
}
}
fn search_meta_section<'a>(
of: &'a ObjectFile,
target: &Target,
filename: &Path,
) -> Result<&'a [u8], String> {
unsafe {
let si = mk_section_iter(of.llof);
while llvm::LLVMIsSectionIteratorAtEnd(of.llof, si.llsi) == False {
let mut name_buf = None;
let name_len = llvm::LLVMRustGetSectionName(si.llsi, &mut name_buf);
let name = name_buf.map_or_else(
String::new, // We got a null ptr, ignore `name_len`.
|buf| {
String::from_utf8(
slice::from_raw_parts(buf.as_ptr() as *const u8, name_len as usize)
.to_vec(),
)
.unwrap()
},
);
debug!("get_metadata_section: name {}", name);
if read_metadata_section_name(target) == name {
let cbuf = llvm::LLVMGetSectionContents(si.llsi);
let csz = llvm::LLVMGetSectionSize(si.llsi) as usize;
// The buffer is valid while the object file is around
let buf: &'a [u8] = slice::from_raw_parts(cbuf as *const u8, csz);
return Ok(buf);
}
llvm::LLVMMoveToNextSection(si.llsi);
}
}
Err(format!("metadata not found: '{}'", filename.display()))
}
pub fn metadata_section_name(target: &Target) -> &'static str {
// Historical note:
//
// When using link.exe it was seen that the section name `.note.rustc`
// was getting shortened to `.note.ru`, and according to the PE and COFF
// specification:
//
// > Executable images do not use a string table and do not support
// > section names longer than 8 characters
//
// https://docs.microsoft.com/en-us/windows/win32/debug/pe-format
//
// As a result, we choose a slightly shorter name! As to why
// `.note.rustc` works on MinGW, that's another good question...
if target.is_like_osx { "__DATA,.rustc" } else { ".rustc" }
}
fn read_metadata_section_name(_target: &Target) -> &'static str {
".rustc"
}