rustc: Fix wasm64 metadata object files · rust-lang/rust@646e8e7 (original) (raw)

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`//! Reading of the rustc metadata for rlibs and dylibs

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use std::borrow::Cow;

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`use std::fs::File;

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`use std::io::Write;

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`use std::path::Path;

`@@ -15,7 +16,6 @@ use rustc_data_structures::owned_slice::{try_slice_owned, OwnedSlice};

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`use rustc_metadata::creader::MetadataLoader;

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`use rustc_metadata::fs::METADATA_FILENAME;

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`use rustc_metadata::EncodedMetadata;

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use rustc_serialize::leb128;

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`use rustc_session::Session;

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`use rustc_span::sym;

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`use rustc_target::abi::Endian;

`@@ -434,12 +434,15 @@ pub enum MetadataPosition {

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`/// automatically removed from the final output.

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`pub fn create_wrapper_file(

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`sess: &Session,

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section_name: Vec,

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section_name: String,

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`data: &[u8],

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`) -> (Vec, MetadataPosition) {

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`let Some(mut file) = create_object_file(sess) else {

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`if sess.target.is_like_wasm {

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return (create_metadata_file_for_wasm(data, &section_name), MetadataPosition::First);

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return (

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create_metadata_file_for_wasm(sess, data, &section_name),

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MetadataPosition::First,

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);

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`// Targets using this branch don't have support implemented here yet or

`@@ -452,7 +455,7 @@ pub fn create_wrapper_file(

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`} else {

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` file.add_section(

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` file.segment_name(StandardSegment::Debug).to_vec(),

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section_name,

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section_name.into_bytes(),

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`SectionKind::Debug,

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`};

`@@ -524,7 +527,7 @@ pub fn create_compressed_metadata_file(

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`let Some(mut file) = create_object_file(sess) else {

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`if sess.target.is_like_wasm {

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return create_metadata_file_for_wasm(&packed_metadata, b".rustc");

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return create_metadata_file_for_wasm(sess, &packed_metadata, ".rustc");

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`return packed_metadata.to_vec();

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`};

`@@ -624,51 +627,41 @@ pub fn create_compressed_metadata_file_for_xcoff(

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`` /// data.

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`///

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`` /// NB: the object crate does not yet have support for writing the wasm

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/// object file format. The format is simple enough that for now an extra crate

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`` -

/// from crates.io (such as wasm-encoder). The file format is:

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`` +

/// object file format. In lieu of that the wasm-encoder crate is used to

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/// build a wasm file by hand.

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`///

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/// * 4-byte header "\0asm"

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/// * 4-byte version number - 1u32 in little-endian format

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/// * concatenated sections, which for this object is always "custom sections"

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///

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/// Custom sections are then defined by:

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/// * 1-byte section identifier - 0 for a custom section

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/// * leb-encoded section length (size of the contents beneath this bullet)

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/// * leb-encoded custom section name length

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/// * custom section name

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/// * section contents

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///

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`` -

/// One custom section, linking, is added here in accordance with

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/// The wasm object file format is defined at

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`/// https://github.com/WebAssembly/tool-conventions/blob/main/Linking.md

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/// which is required to inform LLD that this is an object file but it should

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/// otherwise basically ignore it if it otherwise looks at it. The linking

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/// section currently is defined by a single version byte (2) and then further

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/// sections, but we have no more sections, so it's just the byte "2".

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`` +

/// and mainly consists of a linking custom section. In this case the custom

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/// section there is empty except for a version marker indicating what format

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/// it's in.

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`///

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/// The next custom section is the one we're interested in.

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pub fn create_metadata_file_for_wasm(data: &[u8], section_name: &[u8]) -> Vec {

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let mut bytes = b"\0asm\x01\0\0\0".to_vec();

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-

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let mut append_custom_section = |section_name: &[u8], data: &[u8]| {

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let mut section_name_len = [0; leb128::max_leb128_len::()];

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let off = leb128::write_usize_leb128(&mut section_name_len, section_name.len());

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let section_name_len = &section_name_len[..off];

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-

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let mut section_len = [0; leb128::max_leb128_len::()];

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let off = leb128::write_usize_leb128(

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&mut section_len,

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data.len() + section_name_len.len() + section_name.len(),

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`` +

/// The main purpose of this is to contain a custom section with section_name,

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`` +

/// which is then appended after linking.

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///

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`` +

/// As a further detail the object needs to have a 64-bit memory if wasm64 is

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/// the target or otherwise it's interpreted as a 32-bit object which is

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/// incompatible with 64-bit ones.

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pub fn create_metadata_file_for_wasm(sess: &Session, data: &[u8], section_name: &str) -> Vec {

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assert!(sess.target.is_like_wasm);

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let mut module = wasm_encoder::Module::new();

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let mut imports = wasm_encoder::ImportSection::new();

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+

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if sess.target.pointer_width == 64 {

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imports.import(

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"env",

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"__linear_memory",

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wasm_encoder::MemoryType { minimum: 0, maximum: None, memory64: true, shared: false },

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`);

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let section_len = &section_len[..off];

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-

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bytes.push(0u8);

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bytes.extend_from_slice(section_len);

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bytes.extend_from_slice(section_name_len);

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bytes.extend_from_slice(section_name);

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bytes.extend_from_slice(data);

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};

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}

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append_custom_section(b"linking", &[2]);

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append_custom_section(section_name, data);

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bytes

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if imports.len() > 0 {

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module.section(&imports);

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}

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module.section(&wasm_encoder::CustomSection {

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name: "linking".into(),

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data: Cow::Borrowed(&[2]),

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});

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module.section(&wasm_encoder::CustomSection { name: section_name.into(), data: data.into() });

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module.finish()

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