rust 1.39 and errno
cmusser at sonic.net
Fri Dec 27 21:05:10 PST 2019
I attempted to compile Rust 1.39.0 using the bootstrap repo
(https://github.com/DragonFlyBSD/rust-bootstrap-dragonfly). Tuxillo is
probably already working on this, but I wanted to see if I could
understand the process. I didn't get very far.
After making mods that were pretty obvious (adding checksums, a
subdirectory for the new version, etc.), the build failed when compiling
the getrandom crate. The error was:
error[E0432]: unresolved import `libc::__error`
22 | use libc::__error as errno_location;
| | |
| | help: a similar name exists in the module: `ferror`
| no `__error` in the root
Support for the error variable is somehow tied up in "thread local
storage". I have a vague understanding that every thread has its own
copy of the (traditonally global) errno variable, but I don't understand
what the implications are for supporting it in Rust. There's a tracking
issue in Rust regarding thread local storage, so it's obviously a
non-trivial feature. That issue is
There was a commit to the Rust libc a while back that purported to add
support for a function called __errno_location() for various OSes, but I
think it didn't actually do that for DragonFly. It did add __error, but
not __errno_location(). This was back in July and I don't think such a
function actually existed. The pull request was
More recently, there was a commit to DragonFly itself that did add
__errno_location, so presumably the Rust libc could now really use it.
That commit was
I'd like to gain a better understanding of how all this stuff works. For
- The compile failure says that libc::__error does not exist, but the
libc included in the source does seem to have it defined. Is it
unavailable because thread local storage is disabled?
- Why does the __errno_location() function need to exist? It must differ
somehow from the __error() function.
- As of right now, __errno_location() may only exist in nightly, so I'm
assuming that if Rust's libc glue got updated to reference it, it would
only work correctly for dfly nightlies after that point, and any
subsequent releases (5.8+). Is that correct?
- Many prior version of rustc have been successfuly built for DragonFly.
Did those have something that avoided the use of errno, or is getrandom
a new addition to the build and that's why it's failing?
Thanks for any insight on this stuff,
More information about the Users