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Only link res_init() on GNU/*nix

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To workaround a bug in glibc <= 2.26 lookup_host() calls res_init()
based on the glibc version detected at runtime. While this avoids
calling res_init() on platforms where it's not required we will still
end up linking against the symbol.

This causes an issue on macOS where res_init() is implemented in a
separate library (libresolv.9.dylib) from the main libc. While this is
harmless for standalone programs it becomes a problem if Rust code is
statically linked against another program. If the linked program doesn't
already specify -lresolv it will cause the link to fail. This is
captured in issue #46797

Fix this by hooking in to the glibc workaround in `cvt_gai` and only
activating it for the "gnu" environment on Unix This should include all
glibc platforms while excluding musl, windows-gnu, macOS, FreeBSD, etc.

This has the side benefit of removing the #[cfg] in sys_common; only
unix.rs has code related to the workaround now.
This commit is contained in:
Ryan Cumming
2018-01-10 20:13:03 +11:00
parent 8ff449d505
commit 090a968fe7
3 changed files with 16 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files

24
src/libstd/sys_common/net.rs
View File

@@ -166,27 +166,9 @@ pub fn lookup_host(host: &str) -> io::Result<LookupHost> {
hints.ai_socktype = c::SOCK_STREAM;
let mut res = ptr::null_mut();
unsafe {
match cvt_gai(c::getaddrinfo(c_host.as_ptr(), ptr::null(), &hints, &mut res)) {
Ok(_) => {
Ok(LookupHost { original: res, cur: res })
},
#[cfg(unix)]
Err(e) => {
// If we're running glibc prior to version 2.26, the lookup
// failure could be caused by caching a stale /etc/resolv.conf.
// We need to call libc::res_init() to clear the cache. But we
// shouldn't call it in on any other platform, because other
// res_init implementations aren't thread-safe. See
// https://github.com/rust-lang/rust/issues/41570 and
// https://github.com/rust-lang/rust/issues/43592.
use sys::net::res_init_if_glibc_before_2_26;
let _ = res_init_if_glibc_before_2_26();
Err(e)
},
// the cfg is needed here to avoid an "unreachable pattern" warning
#[cfg(not(unix))]
Err(e) => Err(e),
}
cvt_gai(c::getaddrinfo(c_host.as_ptr(), ptr::null(), &hints, &mut res)).map(|_| {
LookupHost { original: res, cur: res }
})
}
}