Description
rustc appears to have changed the flags it passes to the linker, which has made the order of -l flags significant in a way that they were not before.
Code
First, steps to set up a Cargo project to replicate the problem:
$ cargo new link
$ cd link
$ cat >Cargo.toml <<EOF
[package]
name = "link"
version = "0.1.0"
edition = "2021"
links = "test"
[build-dependencies]
cc = "1"
EOF
$ cat >build.rs <<EOF
fn main() {
println!("cargo:rustc-link-lib=static=test");
cc::Build::new().file("src/foo.c").compile("foo");
}
EOF
$ cat >src/main.rs <<EOF
extern "C" {
fn bar();
}
fn main() {
unsafe { bar() };
}
EOF
$ cat >src/foo.c <<EOF
#include "test.h"
void bar(void) {
version();
}
EOF
$ mkdir .cargo
$ cat >.cargo/config.toml <<EOF
[build]
rustflags = ['-Clink-arg=-Lc/']
[env.LDFLAGS]
value = "-Lc/"
[env.CFLAGS]
value = "-Ic/"
EOF
$ mkdir c
$ echo 'void version();' > c/test.h
$ cat >c/test.c <<EOF
#include "test.h"
void version() {}
EOF
$ cc -c -o c/test.o c/test.c
$ ar rcs c/libtest.a c/test.oWith Rust 1.60.0 installed, this builds and runs fine (cargo b; cargo r).
With Rust 1.61.0 installed, the build errors with:
$ cargo b
Compiling link v0.1.0
error: linking with `cc` failed: exit status: 1
|
= note: "cc" ...
= note: target/debug/build/link-3971cbc394518864/out/libfoo.a(foo.o): In function `bar':
src/foo.c:3: undefined reference to `version'
collect2: error: ld returned 1 exit status
= help: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
= note: use the `-l` flag to specify native libraries to link
= note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-link-libkindname)Flipping the order of the cc invocation and the println! in build.rs fixes the build.
Looking at the output with --verbose, the rustc command that cargo invokes appears to be identical (except for different hashes). Using RUSTC_LOG=rustc_codegen_ssa::back::link=info to get the underlying linker archive, it appears that rustc changed the arguments it passes to the linker under the hood:
-"-Wl,-Bstatic" "-Wl,--whole-archive" "-ltest" "-Wl,--no-whole-archive" "-Wl,--whole-archive" "-lfoo" "-Wl,--no-whole-archive" "-Wl,--start-group"
+"-Wl,-Bstatic" "-ltest" "-lfoo" "-Wl,--start-group"Why exactly this causes the crate to stop compiling when it did previously, I'm not entirely sure, but it is a regression. Flipping the two invocations in build.rs has the effect of flipping the order of the -l static=test and -l static=foo arguments that Cargo passes to rustc, which in turn makes the linker invocation succeed.
Version it worked on
It most recently worked on: 1.60.0
Version with regression
rustc --version --verbose:
rustc 1.61.0 (fe5b13d68 2022-05-18)
binary: rustc
commit-hash: fe5b13d681f25ee6474be29d748c65adcd91f69e
commit-date: 2022-05-18
host: aarch64-unknown-linux-gnu
release: 1.61.0
LLVM version: 14.0.0
The most likely culprit for this appears to be #93901, so cc @petrochenkov.
@rustbot modify labels: +regression-from-stable-to-stable -regression-untriaged