LTO + >=O2 cripples panics

[MageSlayer]

Hi

I am trying to investigate LTO issue.
It appears when I build my project with opt-level = 2 (or 3) and lto = true.
For some reason panics stop working, I mean __rust_maybe_catch_panic is triggered but never returns.

I am under Linux x64 rust compiler nightly-2017-12-07.
Unfortunately I cannot reproduce it in isolation or on any later compiler (due to other regressions).

Any help?

[MageSlayer]

@alexcrichton
Alex, you might be the person to discuss as I found your comments on
#32900

[alexcrichton]

Ah sorry there's not much information to go on here so I'm not sure what's happening :(

You may want to try specifying -Z thinlto=no via RUSTFLAGS if you can, as I think this was around the time that ThinLTO was enabled.

[MageSlayer]

Nope, it does not help.
Looks like compiler somehow generates broken seh.
I can see in gdb that rust_eh_personality is called until some frame.

[MageSlayer]

Related to #48088
Adding #[unwind] to all extern functions fixed the issue with LTO.