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Flare not building on macOS 27.2 #43
Description
Hi! Just reporting what I think is a bug on macOS 27.2
Running mojo build server.mojo gives the following output:
(mojo-webserver) ~/Documents/Development/mojo-webserver/ mojo build server.mojo
ld: warning: object file (/private/var/folders/fg/vb9nsv8x5mb3ksbb25lr0r7r0000gn/T/mojo_archive-3060cb8.a) was built for newer 'macOS' version (27.2) than being linked (27.0)
Undefined symbols for architecture arm64:
"_eventfd_write", referenced from:
_flare::http::_unified_reactor_impl::_accept_loop_unified_fd(::SIMD[DType.int, 1],flare::runtime::reactor::Reactor,::Dict[::SIMD[DType.int, 1], ::SIMD[DType.int, 1], ::AHasher[::SIMD[DType.uint64, 4](0)]],flare::runtime::timer_wheel::TimerWheel,::Dict[::SIMD[DType.int, 1], ::SIMD[DType.uint64, 1], ::AHasher[::SIMD[DType.uint64, 4](0)]],::SIMD[DType.int, 1],::SIMD[DType.int, 1],::SIMD[DType.int, 1],flare::runtime::_balance::Balancer) in mojo_archive-3060cb8.a
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
mojo: error: failed to link executable
Where server.mojo is the following basic example:
from flare.prelude import *
def home(req: Request) -> Response:
return ok("flare is up")
def health(req: Request) -> Response:
return ok_json('{"status":"ok"}')
def greet(req: Request) raises -> Response: # raises: req.param() can
return ok("hello, " + req.param("name"))
def main() raises:
var r = Router()
r.get("/", home)
r.get("/hi/:name", greet)
r.get("/health", health)
var srv = HttpServer.bind(SocketAddr.localhost(8080))
srv.serve(r^)
Similarly, JIT compiling using mojo run server.mojo gives JIT session error: Symbols not found: [ _eventfd_write ]
Activity
ehsanmok commentedon Oct 30, 2026
Thanks for reporting. It's strange! does hello world work on 27.2? I'll try to see if I can repro.
adnlz commentedon Oct 30, 2026
Yeah it's quite odd! Not sure what's causing it, cleaning the build didn't help either, and same error with the hello example from the GitHub readme:
adnlz commentedon Oct 31, 2026
update: I had forgotten to update Xcode command line tools to 27.2, so the following line no longer shows up in the error:
ld: warning: object file (/private/var/folders/fg/vb9nsv8x5mb3ksbb25lr0r7r0000gn/T/mojo_archive-178a6f3.a) was built for newer 'macOS' version (27.2) than being linked (27.0)The rest of the error remains though (undefined symbols for architecture arm64).
It shows that error for both
tag = "v0.13.0"andbranch = "main"like in the following pixi.tomladnlz commentedon Nov 1, 2026
#45 and #44 have fixed this issue :)