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fix(debuginfo): Decompress GNU compressed debug sections correctly #192

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Mar 3, 2020
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fix(debuginfo): Decompress GNU compressed debug sections correctly #192

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33 changes: 24 additions & 9 deletions debuginfo/src/elf.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -254,17 +254,32 @@ impl<'d> ElfObject<'d> {

/// Decompresses the given compressed section data, if supported.
fn decompress_section(&self, section_data: &[u8]) -> Option<Vec<u8>> {
let container = self.elf.header.container().ok()?;
let endianness = self.elf.header.endianness().ok()?;
let context = Ctx::new(container, endianness);
let (size, compressed) = if section_data.starts_with(b"ZLIB") {
// The GNU compression header is a 4 byte magic "ZLIB", followed by an 8-byte big-endian
// size prefix of the decompressed data. This adds up to 12 bytes of GNU header.
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I was confused by the last sentence here because the "up to" made it sound like it can be smaller while the code didn't allow for that.

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Sorry, saw this too late. I can clarify this on master, if you like.

In my mind it read as "the numbers are adding up" to a sum :)

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either way is fine

if section_data.len() < 12 {
return None;
}

let compression = CompressionHeader::parse(&section_data, 0, context).ok()?;
if compression.ch_type != ELFCOMPRESS_ZLIB {
return None;
}
let mut size_bytes = [0; 8];
size_bytes.copy_from_slice(&section_data[4..12]);

(u64::from_be_bytes(size_bytes), &section_data[12..])
} else {
let container = self.elf.header.container().ok()?;
let endianness = self.elf.header.endianness().ok()?;
let context = Ctx::new(container, endianness);

let compression = CompressionHeader::parse(&section_data, 0, context).ok()?;
if compression.ch_type != ELFCOMPRESS_ZLIB {
return None;
}

let compressed = &section_data[CompressionHeader::size(context)..];
(compression.ch_size, compressed)
};

let compressed = &section_data[CompressionHeader::size(context)..];
let mut decompressed = Vec::with_capacity(compression.ch_size as usize);
let mut decompressed = Vec::with_capacity(size as usize);
Decompress::new(true)
.decompress_vec(compressed, &mut decompressed, FlushDecompress::Finish)
.ok()?;
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