-Csave-temps does not retain linker scripts

[nagisa]

Rust uses a linker script with gcc linker flavour, adding a flag like this:

-Wl,--version-script=/run/user/1000/rustcXt0Huw/list

However this file is not preserved even when -Csave-temps is specified, making it impossible to really debug linkage issues outside of rustc.

[Mark-Simulacrum]

I can't reproduce this behavior -- running with -Csave-temps on x86_64-unknown-linux-gnu everything works correctly and the list file is saved. Notably, we do seem to create two temp dirs and only one of them has the relevant file (of course), so maybe that's the odd behavior you were seeing?

I'm testing with rustc 1.38.0-nightly (6e0d27d93 2019-08-03).

I'm going to close this bug so we avoid it sitting open for a long time but feel free to reopen of course!

[nagisa]

I did RUSTFLAGS='-Csave-temps' cargo build --verbose and then ran a rustc command that was invoked in the end. rustc was not able to find the linker file so we either move it somewhere else after we’re done or we fail to save it entirely. Either way the behaviour should be fixed.

[Mark-Simulacrum]

That behavior cannot be fixed unless we introduce -Ctemp-dir or some such as the temp directories are randomly chosen on each run (necessary to avoid conflicts in the common case of multiple simultaneously running rustc instances).

[Mark-Simulacrum]

I'm also not seeing the behavior you noted since AFAICT we don't print the linker invocation unless it fails? This is the output I get:

$ RUSTFLAGS='-Csave-temps' cargo build --verbose
       Fresh unicode-xid v0.1.0
       Fresh proc-macro2 v0.4.30
       Fresh quote v0.6.13
       Fresh syn v0.15.43
       Fresh serde_derive v1.0.98
       Fresh serde v1.0.98
   Compiling test-63142 v0.1.0 (/tmp/test-63142)
     Running `CARGO_PKG_VERSION_MINOR=1 CARGO_PKG_VERSION=0.1.0 CARGO_PKG_HOMEPAGE= CARGO_PKG_REPOSITORY= CARGO_PKG_AUTHORS='Mark Simulacrum <mark.simulacrum@gmail.com>' CARGO_PKG_DESCRIPTION= LD_LIBRARY_PATH='/tmp/test-63142/target/debug/deps:/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib:/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib' CARGO=/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/cargo CARGO_PKG_VERSION_PATCH=0 CARGO_PKG_NAME=test-63142 CARGO_PKG_VERSION_MAJOR=0 CARGO_PKG_VERSION_PRE= CARGO_MANIFEST_DIR=/tmp/test-63142 rustc --edition=2018 --crate-name test_63142 src/lib.rs --color always --crate-type lib --emit=dep-info,metadata,link -C debuginfo=2 -C metadata=d2e51829a2496b97 -C extra-filename=-d2e51829a2496b97 --out-dir /tmp/test-63142/target/debug/deps -C incremental=/tmp/test-63142/target/debug/incremental -L dependency=/tmp/test-63142/target/debug/deps --extern serde_other=/tmp/test-63142/target/debug/deps/libserde-17dac4f520676112.rmeta -Csave-temps`

[nagisa]

I'm also not seeing the behavior you noted since AFAICT we don't print the linker invocation unless it fails?

Well yeah, my original use-case was to debug a linkage issue:

However this file is not preserved even when -Csave-temps is specified, making it impossible to really debug linkage issues outside of rustc.

[Mark-Simulacrum]

$ RUSTFLAGS='-Csave-temps' cargo build --verbose
   Compiling test-63142 v0.1.0 (/tmp/test-63142)
     Running `rustc --edition=2018 --crate-name test_63142 src/main.rs --color always --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=a6bbe65056ed7977 -C extra-filename=-a6bbe65056ed7977 --out-dir /tmp/test-63142/target/debug/deps -C incremental=/tmp/test-63142/target/debug/incremental -L dependency=/tmp/test-63142/target/debug/deps -Csave-temps`
error: linking with `cc` failed: exit code: 1
  |
  = note: "cc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-L" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "/tmp/test-63142/target/debug/deps/test_63142-a6bbe65056ed7977.3jd63e57bat8tsxu.rcgu.o" "/tmp/test-63142/target/debug/deps/test_63142-a6bbe65056ed7977.43jzsajd7h9ghorg.rcgu.o" "/tmp/test-63142/target/debug/deps/test_63142-a6bbe65056ed7977.44xytrbig17godpv.rcgu.o" "/tmp/test-63142/target/debug/deps/test_63142-a6bbe65056ed7977.48i9xpcz1806zq8y.rcgu.o" "/tmp/test-63142/target/debug/deps/test_63142-a6bbe65056ed7977.5ecdjzcoqln51rgw.rcgu.o" "-o" "/tmp/test-63142/target/debug/deps/test_63142-a6bbe65056ed7977" "/tmp/test-63142/target/debug/deps/test_63142-a6bbe65056ed7977.1o4x7pnbg1tzot8k.rcgu.o" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro" "-Wl,-znow" "-nodefaultlibs" "-L" "/tmp/test-63142/target/debug/deps" "-L" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--start-group" "-Wl,-Bstatic" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-2d960816227c2f17.rlib" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-1003bc32a1b5ec74.rlib" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libbacktrace-8a7d2ac0d36f3f8b.rlib" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libbacktrace_sys-6b9f6d6025bf27fd.rlib" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-216e2a71e466ddac.rlib" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-960cbb81128182e0.rlib" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-8d67ca093788450a.rlib" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-8557e66c8e393cdf.rlib" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-1308ce393b2ec00a.rlib" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-981af8f11f107f72.rlib" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-57e0d9e28e683f1a.rlib" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-a57cf95f3d19df20.rlib" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-a7a9d3ce3c155c34.rlib" "-Wl,--end-group" "/home/mark/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-916c11a818639f9e.rlib" "-Wl,-Bdynamic" "-ldl" "-lrt" "-lpthread" "-lgcc_s" "-lc" "-lm" "-lrt" "-lpthread" "-lutil" "-lutil"
  = note: ld: error: undefined symbol: foo_bar
          >>> referenced by main.rs:3 (src/main.rs:3)
          >>>               /tmp/test-63142/target/debug/deps/test_63142-a6bbe65056ed7977.48i9xpcz1806zq8y.rcgu.o:(test_63142::main::hfbbdd4744b783df1)
          collect2: error: ld returned 1 exit status

Running the cc invocation after that works and produces the same output. However, I don't think there's a linker script in that invocation.. I haven't yet been able to come up with an invocation that would generate one on x86_64-unknown-linux-gnu, but admittedly I haven't tried for very long.

[jethrogb]

Triage: still a problem. For example

#[link(name = "nonexist")]
extern "C" {}

#[no_mangle]
pub extern "C" fn hello() {}

rustc -C save-temps --crate-type cdylib lib.rs

Note that the linker script is saved if there's no linker error (if you remove the extern "C" {} block).

[Enselic]

Triage: I think this was fixed by #75315, but I could not find a regression test, so that's all we need before we can close this.