Fix misaligned seek in Reader::skip_bits() #625
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amboar
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Prior to the fix, the newly added test case yields:
$ RUST_LOG=trace cargo test --no-default-features --features=alloc,bits,logging --test test_lsb_le -- test_misaligned_pad_bits_aaelf32_flags
Finished `test` profile [unoptimized + debuginfo] target(s) in 0.03s
Running tests/test_lsb_le.rs (target/debug/deps/test_lsb_le-f72cea0c554eeb76)
running 1 test
[2025-11-24T01:58:46Z TRACE deku::reader] skip_bits: 9
[2025-11-24T01:58:46Z TRACE deku::reader] seek: Current(1)
[2025-11-24T01:58:46Z TRACE deku::reader] read_bits_into: Lsb0, 1
[2025-11-24T01:58:46Z TRACE test_lsb_le] Reading: AaElf32Flags.ef_arm_abi_float_soft
[2025-11-24T01:58:46Z TRACE deku::reader] read_bits_into: Lsb0, 1
[2025-11-24T01:58:46Z TRACE test_lsb_le] Reading: AaElf32Flags.ef_arm_abi_float_hard
[2025-11-24T01:58:46Z TRACE deku::reader] read_bits_into: Lsb0, 1
[2025-11-24T01:58:46Z TRACE deku::reader] skip_bits: 11
[2025-11-24T01:58:46Z TRACE deku::reader] read_bits_into: Lsb0, 3
[2025-11-24T01:58:46Z TRACE deku::reader] seek: Current(1)
[2025-11-24T01:58:46Z TRACE deku::reader] read_bits_into: Lsb0, 0
[2025-11-24T01:58:46Z TRACE test_lsb_le] Reading: AaElf32Flags.ef_arm_gccmask
[2025-11-24T01:58:46Z TRACE deku::reader] read_bits_into: Lsb0, 1
[2025-11-24T01:58:46Z TRACE test_lsb_le] Reading: AaElf32Flags.ef_arm_be8
[2025-11-24T01:58:46Z TRACE deku::reader] read_bits_into: Lsb0, 1
[2025-11-24T01:58:46Z TRACE test_lsb_le] Reading: AaElf32Flags.ef_arm_abimask
[2025-11-24T01:58:46Z TRACE deku::reader] read_bits_into: Lsb0, 8
test test_misaligned_pad_bits_aaelf32_flags ... FAILED
This boils down to an seek where we're not yet byte-aligned. The
addition of:
@@ -207,6 +207,7 @@ impl<R: Read + Seek> Reader<R> {
// first, seek with bytes
if bytes_amt != 0 {
+ debug_assert_eq!(self.bits_read % 8, 0);
self.seek(SeekFrom::Current(
i64::try_from(bytes_amt).expect("could not convert seek usize into i64"),
))
yields:
$ cargo test --no-default-features --features=alloc,bits,logging --test test_lsb_le -- test_misaligned_pad_bits_aaelf32_flags
Finished `test` profile [unoptimized + debuginfo] target(s) in 0.03s
Running tests/test_lsb_le.rs (target/debug/deps/test_lsb_le-f72cea0c554eeb76)
running 1 test
test test_misaligned_pad_bits_aaelf32_flags ... FAILED
failures:
---- test_misaligned_pad_bits_aaelf32_flags stdout ----
thread 'test_misaligned_pad_bits_aaelf32_flags' (131091) panicked at /home/andrew/src/github.com/sharksforarms/deku/src/reader.rs:210:17:
assertion `left == right` failed
left: 6
right: 0
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
failures:
test_misaligned_pad_bits_aaelf32_flags
test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 8 filtered out; finished in 0.00s
Account for alignment in Reader::skip_bits() prior to deriving the range
over which to seek.
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
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Addresses the observation at #617 (comment)