println! segfaults with nightly-2018-06-24 on macOS 10.10 #51758
Description
Update: this is due to LLVM assuming 16-byte alignment for a #[thread_local] static that is in fact 8-bytes aligned. Bisected PR might not be directly related, and might only have moved the static from a location that happened to be 16-bytes aligned by chance?
$ echo 'fn main() { println!("") }' > a.rs $ rustup run --install nightly-2018-06-24 rustc a.rs $ ./a Segmentation fault: 11 $ lldb a (lldb) target create "a" Current executable set to 'a' (x86_64). (lldb) run Process 26778 launched: '/private/tmp/aa/a' (x86_64) Process 26778 stopped * thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=EXC_I386_GPFLT) frame #0: 0x000000010000a565 a`std::io::stdio::_print::h8f28cebade0a06e8 + 197 a`std::io::stdio::_print::h8f28cebade0a06e8: -> 0x10000a565 <+197>: movdqa 0x10(%rax), %xmm0 0x10000a56a <+202>: xorps %xmm1, %xmm1 0x10000a56d <+205>: movaps %xmm1, 0x10(%rax) 0x10000a571 <+209>: movl $0x1, %ecx Target 0: (a) stopped. (lldb) bt * thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=EXC_I386_GPFLT) * frame #0: 0x000000010000a565 a`std::io::stdio::_print::h8f28cebade0a06e8 + 197 frame #1: 0x0000000100000b2f a`a::main::h1162ee7c6f50d0b5 + 63 frame #2: 0x0000000100000ada a`std::rt::lang_start::_$u7b$$u7b$closure$u7d$$u7d$::hdecedfffbbfc4ed3 + 10 frame #3: 0x000000010000e8c8 a`std::panicking::try::do_call::h586091eb2188e424 (.llvm.4887162513922290480) + 24 frame #4: 0x000000010001af0f a`__rust_maybe_catch_panic + 31 frame #5: 0x0000000100007712 a`std::rt::lang_start_internal::h5f9decd422205a6f + 242 frame #6: 0x0000000100000ab5 a`std::rt::lang_start::ha7a5b042430cd1ae + 53 frame #7: 0x0000000100000b65 a`main + 37 frame #8: 0x00007fffcd189235 libdyld.dylib`start + 1Reproduced on three CI builders with macOS 10.10.5, but not on two with 10.11.6.
Not reproduced with the previous Nightly, nightly-2018-06-23. Commit range: cbc4c83...60efbde. Of the PRs merged in this range, eliminating those I’m fairly certain are unrelated leaves #51696 and #51723 which I think are unrelated but am less confident about, and #51580 which touched 69 files in 19 commits.
(Found while upgrading Servo to today’s Nightly: servo/servo#21089 (comment).)