Bug 2272267

The test suite of the "glib" crate started failing in Fedora with segmentation faults. It is possible to track this back to the update from Rust 1.75 to Rust 1.76, across all current branches of Fedora:

https://koschei.fedoraproject.org/package/rust-glib

The following tests now cause segmentation faults (list updated for glib v0.19.3):

- variant_iter::tests::test_variant_iter_array (a --lib test)
- variant_iter::tests::test_variant_str_iter_last (a --lib test)
- variant_iter::tests::test_variant_str_iter_nth (a --lib test)
- variant::Variant::array_iter_str (a --doc test)

The error message looks something like this:

"""
error: test failed, to rerun pass `--lib`
Caused by:
  process didn't exit successfully: `/builddir/build/BUILD/glib-0.18.5/target/rpm/deps/glib-8a813dbb6056e1aa --skip structured_log` (signal: 11, SIGSEGV: invalid memory reference)
"""

Since the test harness is killed by the SIGSEGV, the output of "cargo test" does not actually show the failing test. I isolated the failure cases by running the tests with "--test-threads 1" and added known bad cases with "--skip" until the test suite passed.

The "structured_log" test always fails - it expects some paths to match the workspace layout in the upstream git repository. It can be skipped and is not relevant to this issue.

============================================================

Test code for the first three failing tests is in this file upstream (which has not been changed in the last two years):
https://github.com/gtk-rs/gtk-rs-core/blob/master/glib/src/variant_iter.rs#L204

Test code for the failing doctest is in this file upstream:
https://github.com/gtk-rs/gtk-rs-core/blob/master/glib/src/variant.rs#L843

============================================================

I tried the following scenarios to reproduce the issue (always running "cargo clean" inbetween):

1. system rustc (1.77.0 on Fedora 39):

a. "/usr/bin/cargo test --release -- --skip structured_log": crashes
b. "cargo +system test --release -- --skip structured_log": passes (system = linked toolchain at /usr)

(I have *no idea* how case 1.a and 1.b can behave differently.)

2. rustup toolchains:

a. "cargo +stable test --release -- --skip structured_log": passes (stable = 1.77.1 (7cf61ebde 2024-03-27))
b. "cargo +beta test --release -- --skip structured_log": crashes (beta = 1.78.0-beta.3 (4147533e0 2024-03-27))
c. "cargo +nightly test --release -- --skip structured_log": crashes (nightly = 1.79.0-nightly (c9f8f3438 2024-03-27))

3. different compiler flags for system rustc (1.77.0 on Fedora 39):

a. "RUSTFLAGS="-Copt-level=1" /usr/bin/cargo test -- --skip structured_log": passes
b. "RUSTFLAGS="-Copt-level=2" /usr/bin/cargo test -- --skip structured_log": crashes
c. "RUSTFLAGS="-Copt-level=3" /usr/bin/cargo test -- --skip structured_log": crashes

4. different compiler flags for rustup toolchains:

a. "RUSTFLAGS="-Copt-level=1" cargo +stable test -- --skip structured_log": passes
b. "RUSTFLAGS="-Copt-level=2" cargo +stable test -- --skip structured_log": passes
c. "RUSTFLAGS="-Copt-level=3" cargo +stable test -- --skip structured_log": passes
d. "RUSTFLAGS="-Copt-level=1" cargo +beta test -- --skip structured_log": passes
e. "RUSTFLAGS="-Copt-level=2" cargo +beta test -- --skip structured_log": crashes
f. "RUSTFLAGS="-Copt-level=3" cargo +beta test -- --skip structured_log": crashes
g. "RUSTFLAGS="-Copt-level=1" cargo +nightly test -- --skip structured_log": passes
h. "RUSTFLAGS="-Copt-level=2" cargo +nightly test -- --skip structured_log": crashes
i. "RUSTFLAGS="-Copt-level=3" cargo +nightly test -- --skip structured_log": crashes

============================================================

I cannot determine why the Fedora Rust toolchain seems to have introduced this issue with Rust 1.76, whereas upstream rust toolchains only start exhibiting it with Rust 1.78.0 beta.

I don't think different LLVM versions should be the cause, since the crashes started happening with Rust 1.76 across all branches of Fedora, where

- on Fedora Rawhide, rustc links LLVM 18,
- on Fedora 39 and 40, rustc links LLVM 17, and
- on Fedora 38, rustc links LLVM 16.

Maybe the glib crate has some UB which is only triggered by optimizations in recent Rust releases? But that wouldn't necessarily explain why the Fedora and the upstream toolchains behave differently.


Reproducible: Always

Steps to Reproduce:
1. unpack sources for the "glib" crate
2. run "/usr/bin/cargo test --release"
Actual Results:  
Tests pass.

Expected Results:  
Test runner segfaults.