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rustc: Fail fast when compiling a source file larger than 4 GiB #132791

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merged 1 commit into from
Nov 24, 2024
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rustc: Fail fast when compiling a source file larger than 4 GiB #132791

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5 changes: 5 additions & 0 deletions compiler/rustc_span/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1843,6 +1843,8 @@ impl StableSourceFileId {
}

impl SourceFile {
const MAX_FILE_SIZE: u32 = u32::MAX - 1;
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why the -1 here?

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See #132862

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This PR is fail fast for files LARGER than 4 GiB. 4GiB is 2^32B is (u32::MAX + 1) bytes, so U32::MAX is 4Gi - 1, and U32::MAX - 1 is 4Gi - 2. What is the purpose of a constant for 4GiB - 2B when preventing use of files larger than 4GiB? Is that not off by 2?

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Originally this PR was for enforcing that files of size 4 GiB and larger would not work, meaning the maximum file size would be 4 GiB - 1 B = u32::MAX bytes.

However, I then discovered #132862, so files of size 4 GiB - 1 B and larger would not work, so the maximum file size is actually 4 GiB - 2 B = u32::MAX - 1. So no the current value is correct.

I've just tested this again to make sure. Using the current stable and nightly version of rustc, I get the following results:

File size (bytes) stable result nightly result
4,294,967,294 success success
4,294,967,295 ICE (#132862) instant failure
4,294,967,296 failure after reading the file to memory instant failure


pub fn new(
name: FileName,
mut src: String,
Expand All @@ -1863,6 +1865,9 @@ impl SourceFile {
let stable_id = StableSourceFileId::from_filename_in_current_crate(&name);
let source_len = src.len();
let source_len = u32::try_from(source_len).map_err(|_| OffsetOverflowError)?;
if source_len > Self::MAX_FILE_SIZE {
return Err(OffsetOverflowError);
}

let (lines, multibyte_chars) = analyze_source_file::analyze_source_file(&src);

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11 changes: 10 additions & 1 deletion compiler/rustc_span/src/source_map.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -115,6 +115,12 @@ impl FileLoader for RealFileLoader {
}

fn read_file(&self, path: &Path) -> io::Result<String> {
if path.metadata().is_ok_and(|metadata| metadata.len() > SourceFile::MAX_FILE_SIZE.into()) {
return Err(io::Error::other(format!(
"text files larger than {} bytes are unsupported",
SourceFile::MAX_FILE_SIZE
)));
}
fs::read_to_string(path)
}

Expand Down Expand Up @@ -297,7 +303,10 @@ impl SourceMap {
/// unmodified.
pub fn new_source_file(&self, filename: FileName, src: String) -> Lrc<SourceFile> {
self.try_new_source_file(filename, src).unwrap_or_else(|OffsetOverflowError| {
eprintln!("fatal error: rustc does not support files larger than 4GB");
eprintln!(
"fatal error: rustc does not support text files larger than {} bytes",
SourceFile::MAX_FILE_SIZE
);
crate::fatal_error::FatalError.raise()
})
}
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