segfault on 'index out of bounds' OS X Yosemite

[felipenoris]

I get Segmentation Fault on this code when running the debug binary.

Only happens on OS X Yosemite 10.10.5 .

fn main() {
    let x = [1];
    println!("{}", x[1]);
}

$ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.02s
     Running `target/debug/segfault`
Segmentation fault: 11

$ cargo run --release
    Finished release [optimized] target(s) in 0.02s
     Running `target/release/segfault`
thread 'main' panicked at 'index out of bounds: the len is 1 but the index is 1', src/main.rs:3:20
note: Run with `RUST_BACKTRACE=1` for a backtrace.

Meta

rustc 1.27.0 (3eda71b 2018-06-19)
binary: rustc
commit-hash: 3eda71b
commit-date: 2018-06-19
host: x86_64-apple-darwin
release: 1.27.0
LLVM version: 6.0

[Mark-Simulacrum]

I cannot reproduce on macOS 10.13.5 (High Sierra).

@rust-lang/release if anyone can reproduce and bisect, that would be amazing.

cc @rust-lang/compiler -- stable regression

[kennytm]

I bet it is the same cause as #51758 (misaligned TLS).

[Mark-Simulacrum]

Seems likely -- this is in stable, though, so probably not caused by that. Getting confirmation would be good as well.

[kennytm]

The use of --release matches #50586

[Mark-Simulacrum]

The use of --release matches #50586

This is the reverse of that PR; this bug seems to only happen without --release whereas that one happens only with it.

[nikomatsakis]

This does indeed seem quite bad.

[nikomatsakis]

I cannot reproduce on my laptop, but it is 10.11.6. I'll have to see if I have a machine running 10.10 anywhere.

[kennytm]

@felipenoris Could you load target/debug/segfault into a debugger (gdb or lldb) and get the backtrace when it segfault?

[felipenoris]

Sure. I'll work on that.

[felipenoris]

$ lldb segfault
(lldb) target create "segfault"
Current executable set to 'segfault' (x86_64).
(lldb) run
Process 57139 launched: '/Users/felipenoris/Documents/src/learnrust/segfault/target/debug/segfault' (x86_64)
segfault was compiled with optimization - stepping may behave oddly; variables may not be available.
Process 57139 stopped
* thread #1: tid = 0x793cbc, 0x0000000100011abf segfault`std::panicking::rust_panic_with_hook::hc2253a5bcda7eda7 [inlined] core::ptr::swap_nonoverlapping_bytes::h90af7d9428701cbf + 16 at ptr.rs:237, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=EXC_I386_GPFLT)
    frame #0: 0x0000000100011abf segfault`std::panicking::rust_panic_with_hook::hc2253a5bcda7eda7 [inlined] core::ptr::swap_nonoverlapping_bytes::h90af7d9428701cbf + 16 at ptr.rs:237 [opt]