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Auto merge of #118344 - saethlin:rmeta-header-pos, r=WaffleLapkin

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Use a u64 for the rmeta root position

Waffle noticed this in https://github.com/rust-lang/rust/pull/117301#discussion_r1405410174

We've upgraded the other file offsets to u64, and this one only costs 4 bytes per file. Also the way the truncation was being done before was extremely easy to miss, I sure missed it! It's not clear to me if not having this change effectively made the other upgrades from u32 to u64 ineffective, but we can have it now.

r? `@WaffleLapkin`
This commit is contained in:
bors 2023-12-11 17:21:14 +00:00
commit 4e82988aa2
1 changed files with 18 additions and 13 deletions
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31
crates/proc-macro-api/src/version.rs
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@ -85,8 +85,8 @@ fn read_section<'a>(dylib_binary: &'a [u8], section_name: &str) -> io::Result<&'
}
/// Check the version of rustc that was used to compile a proc macro crate's
///
/// binary file.
///
/// A proc macro crate binary's ".rustc" section has following byte layout:
/// * [b'r',b'u',b's',b't',0,0,0,5] is the first 8 bytes
/// * ff060000 734e6150 is followed, it's the snappy format magic bytes,
@ -96,8 +96,8 @@ fn read_section<'a>(dylib_binary: &'a [u8], section_name: &str) -> io::Result<&'
/// The bytes you get after decompressing the snappy format portion has
/// following layout:
/// * [b'r',b'u',b's',b't',0,0,0,5] is the first 8 bytes(again)
/// * [crate root bytes] next 4 bytes is to store crate root position,
/// according to rustc's source code comment
/// * [crate root bytes] next 8 bytes (4 in old versions) is to store
/// crate root position, according to rustc's source code comment
/// * [length byte] next 1 byte tells us how many bytes we should read next
/// for the version string's utf8 bytes
/// * [version string bytes encoded in utf8] <- GET THIS BOI
@ -119,13 +119,18 @@ pub fn read_version(dylib_path: &AbsPath) -> io::Result<String> {
}
let version = u32::from_be_bytes([dot_rustc[4], dot_rustc[5], dot_rustc[6], dot_rustc[7]]);
// Last supported version is:
// https://github.com/rust-lang/rust/commit/0696e79f2740ad89309269b460579e548a5cd632
let snappy_portion = match version {
5 | 6 => &dot_rustc[8..],
// https://github.com/rust-lang/rust/commit/b94cfefc860715fb2adf72a6955423d384c69318
let (snappy_portion, bytes_before_version) = match version {
5 | 6 => (&dot_rustc[8..], 13),
7 | 8 => {
let len_bytes = &dot_rustc[8..12];
let data_len = u32::from_be_bytes(len_bytes.try_into().unwrap()) as usize;
&dot_rustc[12..data_len + 12]
(&dot_rustc[12..data_len + 12], 13)
}
9 => {
let len_bytes = &dot_rustc[8..16];
let data_len = u64::from_le_bytes(len_bytes.try_into().unwrap()) as usize;
(&dot_rustc[16..data_len + 12], 17)
}
_ => {
return Err(io::Error::new(
@ -142,15 +147,15 @@ pub fn read_version(dylib_path: &AbsPath) -> io::Result<String> {
Box::new(SnapDecoder::new(snappy_portion))
};
// the bytes before version string bytes, so this basically is:
// We're going to skip over the bytes before the version string, so basically:
// 8 bytes for [b'r',b'u',b's',b't',0,0,0,5]
// 4 bytes for [crate root bytes]
// 4 or 8 bytes for [crate root bytes]
// 1 byte for length of version string
// so 13 bytes in total, and we should check the 13th byte
// so 13 or 17 bytes in total, and we should check the last of those bytes
// to know the length
let mut bytes_before_version = [0u8; 13];
uncompressed.read_exact(&mut bytes_before_version)?;
let length = bytes_before_version[12];
let mut bytes = [0u8; 17];
uncompressed.read_exact(&mut bytes[..bytes_before_version])?;
let length = bytes[bytes_before_version - 1];
let mut version_string_utf8 = vec![0u8; length as usize];
uncompressed.read_exact(&mut version_string_utf8)?;