undefined reference link error regression

[alexcrichton]

This looks to be a regression from stable to beta unfortunately, compiling rust-lang/futures-rs@6ae0345 succeeds on stable but fails on beta:

$ rustup run stable cargo build --manifest-path http/Cargo.toml
...
$ rustup run beta cargo build --manifest-path http/Cargo.toml
...
   Compiling http v0.1.0 (file:///home/alex/code/futures/http)
error: linking with `cc` failed: exit code: 1
note: "cc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-L" "/home/alex/.multirust/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "/home/alex/code/futures/http/target/debug/http.0.o" "-o" "/home/alex/code/futures/http/target/debug/http" "-Wl,--gc-sections" "-pie" "-nodefaultlibs" "-L" "/home/alex/code/futures/http/target/debug" "-L" "/home/alex/code/futures/http/target/debug/deps" "-L" "/home/alex/.multirust/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "-Wl,-Bdynamic" "/home/alex/code/futures/http/target/debug/libhttp.rlib" "/home/alex/code/futures/http/target/debug/deps/libhttparse-36b96d90ffbce562.rlib" "/home/alex/code/futures/http/target/debug/deps/libfuturemio-986c91cdeb491b00.rlib" "/home/alex/code/futures/http/target/debug/deps/libslab-45f4a226259c4869.rlib" "/home/alex/code/futures/http/target/debug/deps/libfutures-1a55edc1e7c129de.rlib" "/home/alex/code/futures/http/target/debug/deps/libmio-a89f84904d772c54.rlib" "/home/alex/code/futures/http/target/debug/deps/libnet2-b2390925f9bbf4a2.rlib" "/home/alex/code/futures/http/target/debug/deps/libcfg_if-72c1f992b13d5087.rlib" "/home/alex/code/futures/http/target/debug/deps/libmiow-b827bf6129dcd844.rlib" "/home/alex/code/futures/http/target/debug/deps/libwinapi-0889532d327ff4e2.rlib" "/home/alex/code/futures/http/target/debug/deps/libnix-f8d033ce6354dacb.rlib" "/home/alex/code/futures/http/target/debug/deps/libbytes-f9fbfc75eb2416e0.rlib" "/home/alex/code/futures/http/target/debug/deps/libscoped_tls-53036341d2dbbe26.rlib" "/home/alex/code/futures/http/target/debug/deps/libtime-750bfdd52feafcb7.rlib" "/home/alex/code/futures/http/target/debug/deps/liblibc-1f3392fe1afd1313.rlib" "/home/alex/code/futures/http/target/debug/deps/liblog-bf16bb9a4912b11d.rlib" "/home/alex/code/futures/http/target/debug/deps/libbitflags-e61ad67c3301e77d.rlib" "/home/alex/code/futures/http/target/debug/deps/libslab-4f8b9e9b6e35857c.rlib" "/home/alex/.multirust/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-411fd48b.rlib" "/home/alex/.multirust/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-411fd48b.rlib" "/home/alex/.multirust/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-411fd48b.rlib" "/home/alex/.multirust/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librand-411fd48b.rlib" "/home/alex/.multirust/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcollections-411fd48b.rlib" "/home/alex/.multirust/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_unicode-411fd48b.rlib" "/home/alex/.multirust/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-411fd48b.rlib" "/home/alex/.multirust/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc_jemalloc-411fd48b.rlib" "/home/alex/.multirust/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-411fd48b.rlib" "/home/alex/.multirust/toolchains/beta-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-411fd48b.rlib" "-l" "util" "-l" "dl" "-l" "pthread" "-l" "gcc_s" "-l" "pthread" "-l" "c" "-l" "m" "-l" "rt" "-l" "util" "-l" "compiler-rt"
note: /home/alex/code/futures/http/target/debug/http.0.o: In function `http::serve<http::request::Request,http::response::Response,closure>':
/home/alex/code/futures/http/src/lib.rs:55: undefined reference to `futuremio::tcp::_$LT$impl$u20$futuremio..event_loop..LoopHandle$GT$::tcp_listen::h9a7258751896fb30'
/home/alex/code/futures/http/target/debug/http.0.o: In function `http::serve::_$u7b$$u7b$closure$u7d$$u7d$::hed42a806f41e1837':
http.0.rs:(.text._ZN4http5serve28_$u7b$$u7b$closure$u7d$$u7d$17hed42a806f41e1837E+0xa2): undefined reference to `futuremio::tcp::TcpListener::incoming::h7aae24690b0d3a8d'
/home/alex/code/futures/http/target/debug/http.0.o: In function `futures::forget::forget<futures::then::Then<Box<Future>, core::result::Result<(), std::sync::mpsc::SendError<core::result::Result<(), std::io::error::Error>>>, closure>>':
/home/alex/code/futures/src/forget.rs:23: undefined reference to `futures::forget::_forget::h4301ad1ba69f01dc'
collect2: error: ld returned 1 exit status


error: aborting due to previous error
error: Could not compile `http`.

cc @michaelwoerister, does this look familiar?

I'll try to reduce down as well, but wanted to file an issue nonetheless.

[alexcrichton]

cc @rust-lang/compiler

[alexcrichton]

Ok, minimized:

// foo.rs
#![crate_type = "lib"]
#![crate_name = "foo"]
pub trait Future {
    type Item;
    type Error;
}

fn foo() -> Box<Future<Item=(), Error=Box<()>>> {
    loop {}
}

pub fn bar<F, A, B>(_s: F)
    where F: Fn(A) -> B,
{
    foo();
}

// bar.rs
extern crate foo;

fn mk<T>() -> T { loop {} }

struct Data<T, E> {
    data: T,
    error: E,
}

fn main() {
    foo::bar(|()| {
        Data::<(), std::io::Error> {
            data: mk(),
            error: mk(),
        }
    })
}

$ rustup run stable rustc foo.rs && rustup run stable rustc bar.rs -L .
...
$ rustup run nightly rustc foo.rs && rustup run nightly rustc bar.rs -L .
...
error: linking with `cc` failed: exit code: 1
note: "cc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-L" "/home/alex/.multirust/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "bar.0.o" "-o" "bar" "-Wl,--gc-sections" "-pie" "-nodefaultlibs" "-L" "." "-L" "/home/alex/.multirust/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,-Bstatic" "-Wl,-Bdynamic" "/home/alex/code/futures/libfoo.rlib" "/home/alex/.multirust/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-c8005792.rlib" "/home/alex/.multirust/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-c8005792.rlib" "/home/alex/.multirust/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-c8005792.rlib" "/home/alex/.multirust/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librand-c8005792.rlib" "/home/alex/.multirust/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcollections-c8005792.rlib" "/home/alex/.multirust/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_unicode-c8005792.rlib" "/home/alex/.multirust/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-c8005792.rlib" "/home/alex/.multirust/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc_jemalloc-c8005792.rlib" "/home/alex/.multirust/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-c8005792.rlib" "/home/alex/.multirust/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-c8005792.rlib" "-l" "dl" "-l" "pthread" "-l" "gcc_s" "-l" "pthread" "-l" "c" "-l" "m" "-l" "rt" "-l" "util" "-l" "compiler-rt"
note: bar.0.o: In function `foo::bar::h97da9529975f6f18':
bar.cgu-0.rs:(.text._ZN3foo3bar17h97da9529975f6f18E+0xf): undefined reference to `foo::foo::h4e3fa806e0391cb9'
collect2: error: ld returned 1 exit status

[alexcrichton]

So it looks like the IR for the foo.rs file emits a symbol of the name

_ZN3foo3foo17h024669b567103e37E

Yet when bar.rs is compiled it expects a symbol of the name

_ZN3foo3foo17h4e3fa806e0391cb9E

Seems... bad! I wonder if #33703 is related...

[michaelwoerister]

So, my guess is that both stable and beta compute different symbol names here, but in stable symbol names are still store in metadata and thus we don't see the discrepancy. Why they compute different names, I don't know yet.

[eddyb]

@michaelwoerister If tcx.hash_crate_independent(...) is used for the hash in the symbol name then it's #33703 - @willcrichton said he'd look into fixing that.

[michaelwoerister]

We are hashing the type parameters as they are encoded for metadata, which should be a stable representation.

[michaelwoerister]

So, here is some debug output from symbol hashing:

foo.rs
compute symbol hash:
foo/45447b7afbd5e544f7d0f1df0fccd26014d9850130abd3f020b89ff96b82079f::foo[0]
encoded_item_type: Ffoo/45447b7afbd5e544f7d0f1df0fccd26014d9850130abd3f020b89ff96b82079f::foo[0]|[][][][][][]n[Rust][]N~x[foo/45447b7afbd5e544f7d0f1df0fccd26014d9850130abd3f020b89ff96b82079f::Future[0]|[][][][][][].EPfoo/45447b7afbd5e544f7d0f1df0fccd26014d9850130abd3f020b89ff96b82079f::Future[0]|[][][][][][]Item|T[]Pfoo/45447b7afbd5e544f7d0f1df0fccd26014d9850130abd3f020b89ff96b82079f::Future[0]|[][][][][][]Error|~T[].]
hash: h024669b567103e37


bar.rs
compute symbol hash:
foo/45447b7afbd5e544f7d0f1df0fccd26014d9850130abd3f020b89ff96b82079f::foo[0]
encoded_item_type: Ffoo/45447b7afbd5e544f7d0f1df0fccd26014d9850130abd3f020b89ff96b82079f::foo[0]|[][][][][][]n[Rust][]N~x[foo/45447b7afbd5e544f7d0f1df0fccd26014d9850130abd3f020b89ff96b82079f::Future[0]|[][][][][][].EPfoo/45447b7afbd5e544f7d0f1df0fccd26014d9850130abd3f020b89ff96b82079f::Future[0]|[][][][][][]Error|~T[]Pfoo/45447b7afbd5e544f7d0f1df0fccd26014d9850130abd3f020b89ff96b82079f::Future[0]|[][][][][][]Item|T[].]
hash: h4e3fa806e0391cb9

If you look closely, you might see that the named type parameters are encoded in a different order in the two cases.

[michaelwoerister]

Yeah, it looks like the projection bounds are sorted by DefId:
https://github.com/rust-lang/rust/blob/beta/src/librustc/ty/mod.rs#L1030

[alexcrichton]

@michaelwoerister awesome, thanks for the investigation!