build.rs should ignore RUSTFLAGS

[polachok]

Problem

build.rs is compiled with RUSTFLAGS if target is not specified.

$ RUSTFLAGS="-C target-cpu=nehalem" cargo build -vv
   Compiling test-build v0.1.0 (/Users/plhk/Documents/src/test-build)
     Running `rustc --crate-name build_script_build build.rs --color always --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=8a72131a02621b95 -C extra-filename=-8a72131a02621b95
 --out-dir /Users/plhk/Documents/src/test-build/target/debug/build/test-build-8a72131a02621b95 
-C incremental=/Users/plhk/Documents/src/test-build/target/debug/incremental
-L dependency=/Users/plhk/Documents/src/test-build/target/debug/deps -C target-cpu=nehalem`

The problem here is that if a user compiles for a newer CPU than they have, build script can potentially use newer instructions and fail with SIGILL.

Steps
1.cargo new test-build
2.cd test-build
3.touch build.rs
4.cargo build -vv

Possible Solution(s)
I don't have a solution, but it seems like env_args() is the problem.

Notes

Output of cargo version:

cargo 1.30.0 (a1a4ad3 2018-11-02)

[alexcrichton]

As a workaround I'd recommend passing --target which will disable this behavior. Otherwise this is a well known issue covered by a number of other issues too: #3349, #4423, #5754

[elichai]

I'm still getting error: lto can only be run for executables, cdylibs and static library outputs sometimes even when passing --target
example:
command: RUSTFLAGS+=' -Clto -Ctarget-cpu=native' cargo install --force cargo-crev --target x86_64-unknown-linux-gnu --verbose

output:

     Running `sccache rustc --crate-name openssl_sys /home/elichai2/.cargo/registry/src/github.heygears.com-1ecc6299db9ec823/openssl-sys-0.9.53/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C metadata=80e051d4886f40ee -C extra-filename=-80e051d4886f40ee --out-dir /tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps --target x86_64-unknown-linux-gnu -L dependency=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps -L dependency=/tmp/cargo-installplOv5W/release/deps --extern libc=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps/liblibc-f9604e2813c04637.rmeta --cap-lints allow -Clto -Ctarget-cpu=native --cfg const_fn --cfg 'osslconf="OPENSSL_NO_SSL3_METHOD"' --cfg ossl101 --cfg ossl102 --cfg ossl102f --cfg ossl102h --cfg ossl110 --cfg ossl110f --cfg ossl110g --cfg ossl111 --cfg ossl111b --cfg ossl111c -l ssl -l crypto`
     Running `/tmp/cargo-installplOv5W/release/build/libssh2-sys-da404dcad10cbb4b/build-script-build`
     Running `/tmp/cargo-installplOv5W/release/build/openssl-9d46d869025e0183/build-script-build`
     Running `/tmp/cargo-installplOv5W/release/build/native-tls-768c28bd77a5ca54/build-script-build`
error: lto can only be run for executables, cdylibs and static library outputs

error: aborting due to previous error

error: could not compile `miscreant`.

Caused by:
  process didn't exit successfully: `sccache rustc --edition=2018 --crate-name miscreant /home/elichai2/.cargo/registry/src/github.heygears.com-1ecc6299db9ec823/miscreant-0.4.2/src/lib.rs --color never --crate-type rlib --crate-type staticlib --emit=dep-info,link -C opt-level=3 --cfg 'feature="aes"' --cfg 'feature="alloc"' --cfg 'feature="byteorder"' --cfg 'feature="default"' --cfg 'feature="soft-aes"' --cfg 'feature="std"' --cfg 'feature="stream"' -C metadata=eb7b7ea891b79345 -C extra-filename=-eb7b7ea891b79345 --out-dir /tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps --target x86_64-unknown-linux-gnu -L dependency=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps -L dependency=/tmp/cargo-installplOv5W/release/deps --extern aes=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps/libaes-59bc26c48e377af1.rlib --extern aesni=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps/libaesni-b0a0a29efbc7f08e.rlib --extern byteorder=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps/libbyteorder-379311baed87428e.rlib --extern cmac=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps/libcmac-51c758923f362247.rlib --extern crypto_mac=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps/libcrypto_mac-c71872e5c18ce69b.rlib --extern ctr=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps/libctr-840349a39310199e.rlib --extern dbl=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps/libdbl-3fb84d3a157ed756.rlib --extern generic_array=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps/libgeneric_array-075965c8c4c8ace9.rlib --extern pmac=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps/libpmac-d83af01cf6d8859c.rlib --extern stream_cipher=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps/libstream_cipher-701a688a1df56cd4.rlib --extern subtle=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps/libsubtle-7d7c1d3bbdcf00ab.rlib --extern zeroize=/tmp/cargo-installplOv5W/x86_64-unknown-linux-gnu/release/deps/libzeroize-afe337c85ef76089.rlib --cap-lints allow -Clto -Ctarget-cpu=native` (exit code: 1)
warning: build failed, waiting for other jobs to finish...
error: failed to compile `cargo-crev v0.13.0`, intermediate artifacts can be found at `/tmp/cargo-installplOv5W`

Caused by:
  build failed

full output: https://pastebin.com/raw/0fPA4Mhz

[ehuss]

@elichai It looks like miscreant specifies multiple crate types (rlib/staticlib). LTO doesn't support that. You need to specify lto in the Cargo profile so that Cargo will handle passing the flag at the correct time.

[elichai]

@elichai It looks like miscreant specifies multiple crate types (rlib/staticlib). LTO doesn't support that. You need to specify lto in the Cargo profile so that Cargo will handle passing the flag at the correct time.

How can I do that without editing Cargo.toml? (i.e. I have a script that adds ' -Clto -Ctarget-cpu=native' to all of my installs)

[ehuss]

Config profiles support that, but unfortunately they are unstable/unfinished.

CARGO_PROFILE_RELEASE_LTO=true cargo install foo -Zconfig-profile

[andrewbaxter]

For anyone else who hits the issue, the workaround is to

1. Specify RUSTFLAGS as an environment variable when invoking cargo and
2. Specify --target, which disables using the env var for build.rs (it will be used for building the binary).

Note that this does not work with rustflags = [...] in cargo/config.toml AFAICT, it must be done with the environment variable.

[mert-kurttutan]

Here I am putting a minimal example I have that gives this problem (that is reproducible on a Ubuntu machine, rustc rustc 1.70.0) in case someone finds it useful:

// build.rs                                                                         
fn main(){
    println!("Hello world!");
    let version = "rustc 1.70.0 1-(05".to_owned();
    let nightly = version.contains("dev");
    println!("End of world!");
}

// .cargo/config.toml
[target.x86_64-unknown-linux-gnu]
rustflags = ["-C", "target-feature=+avx512f"]

The problem goes away if you change version to

let version = "rustc 1.70.0 1-".to_owned();