This commit is targeted at addressing #48251 by specifically fixing a case where
a longjmp over Rust frames on MSVC runs cleanups, accidentally running the
"abort the program" cleanup as well. Added in #46833 `extern` ABI functions in
Rust will abort the process if Rust panics, and currently this is modeled as a
normal cleanup like all other destructors.
Unfortunately it turns out that `longjmp` on MSVC is implemented with SEH, the
same mechanism used to implement panics in Rust. This means that `longjmp` over
Rust frames will run Rust cleanups (even though we don't necessarily want it
to). Notably this means that if you `longjmp` over a Rust stack frame then that
probably means you'll abort the program because one of the cleanups will abort
the process.
After some discussion on IRC it turns out that `longjmp` doesn't run cleanups
for *caught* exceptions, it only runs cleanups for cleanup pads. Using this
information this commit tweaks the codegen for an `extern` function to
a catch-all clause for exceptions instead of a cleanup block. This catch-all is
equivalent to the C++ code:
try {
foo();
} catch (...) {
bar();
}
and in fact our codegen here is designed to match exactly what clang emits for
that C++ code!
With this tweak a longjmp over Rust code will no longer abort the process. A
longjmp will continue to "accidentally" run Rust cleanups (destructors) on MSVC.
Other non-MSVC platforms will not rust destructors with a longjmp, so we'll
probably still recommend "don't have destructors on the stack", but in any case
this is a more surgical fix than #48567 and should help us stick to standard
personality functions a bit longer.
Given a trait predicate, if all params appearing in the LHS have
defaults then it should be a backwards compatible predicate. We verify
that by checking the WF of predicate with all defaults substituted
simultaneously.
Fix FreeBSD struct returning ABI.
FreeBSD has had a patch similar to this for a while. See https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=223047.
This reworks 6774e7a to be more specific about what `compute_abi_info` is checking for per target.
Fix error-format to properly send JSON to stdout
Since we take Cargo's JSON messages as well we need to specifically send
rustc's messages out so we don't hide them.
r? @Manishearth
Ensure main() always has external linkage
This ensures that the entry function is never elided due to inlining, even with `inline(always)`. Fixes#47783.
There were a couple of possible ways of addressing this issue; I simply picked the one that seemed most direct. A warning could be appropriate, but considering using inlining hints in other places it doesn't apply also throws no warnings, and it seems like an edge case anyway, I haven't added one for now.
