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Add `x86_64-unikraft-linux-musl` target

This introduces `x86_64-unikraft-linux-musl` as the first Rust target for the [Unikraft] Unikernel Development Kit.

[Unikraft]: https://unikraft.org/

Unikraft imitates Linux and uses musl as libc.
It is extremely configurable, and does not even provide a `poll` implementation or a network stack, unless enabled by the end user who compiles the application.

Our approach for integrating the build process with `rustc` is to hide the build process as well as the actual final linking step behind a linker-shim (`kraftld`, see unikraft/kraftkit#612).

## Tier 3 target policy

> - A tier 3 target must have a designated developer or developers (the "target
>   maintainers") on record to be CCed when issues arise regarding the target.
>   (The mechanism to track and CC such developers may evolve over time.)

I will be the target maintainer.

> - Targets must use naming consistent with any existing targets; for instance, a
>   target for the same CPU or OS as an existing Rust target should use the same
>   name for that CPU or OS. Targets should normally use the same names and
>   naming conventions as used elsewhere in the broader ecosystem beyond Rust
>   (such as in other toolchains), unless they have a very good reason to
>   diverge. Changing the name of a target can be highly disruptive, especially
>   once the target reaches a higher tier, so getting the name right is important
>   even for a tier 3 target.
>   - Target names should not introduce undue confusion or ambiguity unless
>     absolutely necessary to maintain ecosystem compatibility. For example, if
>     the name of the target makes people extremely likely to form incorrect
>     beliefs about what it targets, the name should be changed or augmented to
>     disambiguate it.
>   - If possible, use only letters, numbers, dashes and underscores for the name.
>     Periods (`.`) are known to cause issues in Cargo.

The target name `x86_64-unikraft-linux-musl` was derived from `x86_64-unknown-linux-musl`, setting Unikraft as vendor.
Unikraft exactly imitates Linux + musl.

> - Tier 3 targets may have unusual requirements to build or use, but must not
>   create legal issues or impose onerous legal terms for the Rust project or for
>   Rust developers or users.
>   - The target must not introduce license incompatibilities.
>   - Anything added to the Rust repository must be under the standard Rust
>     license (`MIT OR Apache-2.0`).
>   - The target must not cause the Rust tools or libraries built for any other
>     host (even when supporting cross-compilation to the target) to depend
>     on any new dependency less permissive than the Rust licensing policy. This
>     applies whether the dependency is a Rust crate that would require adding
>     new license exceptions (as specified by the `tidy` tool in the
>     rust-lang/rust repository), or whether the dependency is a native library
>     or binary. In other words, the introduction of the target must not cause a
>     user installing or running a version of Rust or the Rust tools to be
>     subject to any new license requirements.
>   - Compiling, linking, and emitting functional binaries, libraries, or other
>     code for the target (whether hosted on the target itself or cross-compiling
>     from another target) must not depend on proprietary (non-FOSS) libraries.
>     Host tools built for the target itself may depend on the ordinary runtime
>     libraries supplied by the platform and commonly used by other applications
>     built for the target, but those libraries must not be required for code
>     generation for the target; cross-compilation to the target must not require
>     such libraries at all. For instance, `rustc` built for the target may
>     depend on a common proprietary C runtime library or console output library,
>     but must not depend on a proprietary code generation library or code
>     optimization library. Rust's license permits such combinations, but the
>     Rust project has no interest in maintaining such combinations within the
>     scope of Rust itself, even at tier 3.
>   - "onerous" here is an intentionally subjective term. At a minimum, "onerous"
>     legal/licensing terms include but are *not* limited to: non-disclosure
>     requirements, non-compete requirements, contributor license agreements
>     (CLAs) or equivalent, "non-commercial"/"research-only"/etc terms,
>     requirements conditional on the employer or employment of any particular
>     Rust developers, revocable terms, any requirements that create liability
>     for the Rust project or its developers or users, or any requirements that
>     adversely affect the livelihood or prospects of the Rust project or its
>     developers or users.

No dependencies were added to Rust.
Requirements for linking are [Unikraft] and [KraftKit] (both BSD-3-Clause), but none of these are added to Rust.

[KraftKit]: https://github.com/unikraft/kraftkit

> - Neither this policy nor any decisions made regarding targets shall create any
>   binding agreement or estoppel by any party. If any member of an approving
>   Rust team serves as one of the maintainers of a target, or has any legal or
>   employment requirement (explicit or implicit) that might affect their
>   decisions regarding a target, they must recuse themselves from any approval
>   decisions regarding the target's tier status, though they may otherwise
>   participate in discussions.
>   - This requirement does not prevent part or all of this policy from being
>     cited in an explicit contract or work agreement (e.g. to implement or
>     maintain support for a target). This requirement exists to ensure that a
>     developer or team responsible for reviewing and approving a target does not
>     face any legal threats or obligations that would prevent them from freely
>     exercising their judgment in such approval, even if such judgment involves
>     subjective matters or goes beyond the letter of these requirements.

Understood.
I am not a member of a Rust team.

> - Tier 3 targets should attempt to implement as much of the standard libraries
>   as possible and appropriate (`core` for most targets, `alloc` for targets
>   that can support dynamic memory allocation, `std` for targets with an
>   operating system or equivalent layer of system-provided functionality), but
>   may leave some code unimplemented (either unavailable or stubbed out as
>   appropriate), whether because the target makes it impossible to implement or
>   challenging to implement. The authors of pull requests are not obligated to
>   avoid calling any portions of the standard library on the basis of a tier 3
>   target not implementing those portions.

Understood.
`std` is supported.

> - The target must provide documentation for the Rust community explaining how
>   to build for the target, using cross-compilation if possible. If the target
>   supports running binaries, or running tests (even if they do not pass), the
>   documentation must explain how to run such binaries or tests for the target,
>   using emulation if possible or dedicated hardware if necessary.

Building is described in the platform support doc.
It will be updated once proper `kraftld` support has landed.

> - Tier 3 targets must not impose burden on the authors of pull requests, or
>   other developers in the community, to maintain the target. In particular,
>   do not post comments (automated or manual) on a PR that derail or suggest a
>   block on the PR based on a tier 3 target. Do not send automated messages or
>   notifications (via any medium, including via ``@`)` to a PR author or others
>   involved with a PR regarding a tier 3 target, unless they have opted into
>   such messages.
>   - Backlinks such as those generated by the issue/PR tracker when linking to
>     an issue or PR are not considered a violation of this policy, within
>     reason. However, such messages (even on a separate repository) must not
>     generate notifications to anyone involved with a PR who has not requested
>     such notifications.

Understood.

> - Patches adding or updating tier 3 targets must not break any existing tier 2
>   or tier 1 target, and must not knowingly break another tier 3 target without
>   approval of either the compiler team or the maintainers of the other tier 3
>   target.
>   - In particular, this may come up when working on closely related targets,
>     such as variations of the same architecture with different features. Avoid
>     introducing unconditional uses of features that another variation of the
>     target may not have; use conditional compilation or runtime detection, as
>     appropriate, to let each target run code supported by that target.

I don't think this PR breaks anything.

r? compiler-team
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bors committed Jul 25, 2023
2 parents beef07f + 5538047 commit d24c4da
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Showing 11 changed files with 124 additions and 3 deletions.
3 changes: 3 additions & 0 deletions compiler/rustc_target/src/spec/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -85,6 +85,7 @@ mod solaris_base;
mod solid_base;
mod thumb_base;
mod uefi_msvc_base;
mod unikraft_linux_musl_base;
mod vxworks_base;
mod wasm_base;
mod windows_gnu_base;
Expand Down Expand Up @@ -1421,6 +1422,8 @@ supported_targets! {
("riscv64gc-unknown-hermit", riscv64gc_unknown_hermit),
("x86_64-unknown-hermit", x86_64_unknown_hermit),

("x86_64-unikraft-linux-musl", x86_64_unikraft_linux_musl),

("riscv32i-unknown-none-elf", riscv32i_unknown_none_elf),
("riscv32im-unknown-none-elf", riscv32im_unknown_none_elf),
("riscv32imc-unknown-none-elf", riscv32imc_unknown_none_elf),
Expand Down
15 changes: 15 additions & 0 deletions compiler/rustc_target/src/spec/unikraft_linux_musl_base.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,15 @@
use crate::spec::{cvs, PanicStrategy, RelocModel, TargetOptions};

pub fn opts() -> TargetOptions {
TargetOptions {
os: "linux".into(),
env: "musl".into(),
vendor: "unikraft".into(),
linker: Some("kraftld".into()),
relocation_model: RelocModel::Static,
families: cvs!["unix"],
has_thread_local: true,
panic_strategy: PanicStrategy::Abort,
..Default::default()
}
}
19 changes: 19 additions & 0 deletions compiler/rustc_target/src/spec/x86_64_unikraft_linux_musl.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
use crate::spec::{Cc, LinkerFlavor, Lld, StackProbeType, Target, TargetOptions};

pub fn target() -> Target {
Target {
llvm_target: "x86_64-unknown-linux-musl".into(),
pointer_width: 64,
arch: "x86_64".into(),
data_layout: "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
.into(),
options: TargetOptions {
cpu: "x86-64".into(),
plt_by_default: false,
pre_link_args: TargetOptions::link_args(LinkerFlavor::Gnu(Cc::Yes, Lld::No), &["-m64"]),
max_atomic_width: Some(64),
stack_probes: StackProbeType::X86,
..super::unikraft_linux_musl_base::opts()
},
}
}
14 changes: 13 additions & 1 deletion library/std/src/sys/unix/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -110,6 +110,11 @@ pub unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
while libc::poll(pfds.as_mut_ptr(), 3, 0) == -1 {
match errno() {
libc::EINTR => continue,
#[cfg(target_vendor = "unikraft")]
libc::ENOSYS => {
// Not all configurations of Unikraft enable `LIBPOSIX_EVENT`.
break 'poll;
}
libc::EINVAL | libc::EAGAIN | libc::ENOMEM => {
// RLIMIT_NOFILE or temporary allocation failures
// may be preventing use of poll(), fall back to fcntl
Expand Down Expand Up @@ -165,7 +170,14 @@ pub unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
}

unsafe fn reset_sigpipe(#[allow(unused_variables)] sigpipe: u8) {
#[cfg(not(any(target_os = "emscripten", target_os = "fuchsia", target_os = "horizon")))]
#[cfg(not(any(
target_os = "emscripten",
target_os = "fuchsia",
target_os = "horizon",
// Unikraft's `signal` implementation is currently broken:
// https://github.com/unikraft/lib-musl/issues/57
target_vendor = "unikraft",
)))]
{
// We don't want to add this as a public type to std, nor do we
// want to `include!` a file from the compiler (which would break
Expand Down
2 changes: 1 addition & 1 deletion src/bootstrap/compile.rs
Original file line number Diff line number Diff line change
Expand Up @@ -261,7 +261,7 @@ fn copy_self_contained_objects(
// to using gcc from a glibc-targeting toolchain for linking.
// To do that we have to distribute musl startup objects as a part of Rust toolchain
// and link with them manually in the self-contained mode.
if target.contains("musl") {
if target.contains("musl") && !target.contains("unikraft") {
let srcdir = builder.musl_libdir(target).unwrap_or_else(|| {
panic!("Target {:?} does not have a \"musl-libdir\" key", target.triple)
});
Expand Down
2 changes: 2 additions & 0 deletions src/bootstrap/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -131,6 +131,8 @@ const EXTRA_CHECK_CFGS: &[(Option<Mode>, &'static str, Option<&[&'static str]>)]
(Some(Mode::Std), "freebsd13", None),
(Some(Mode::Std), "backtrace_in_libstd", None),
/* Extra values not defined in the built-in targets yet, but used in std */
// #[cfg(bootstrap)]
(Some(Mode::Std), "target_vendor", Some(&["unikraft"])),
(Some(Mode::Std), "target_env", Some(&["libnx"])),
// (Some(Mode::Std), "target_os", Some(&[])),
// #[cfg(bootstrap)] mips32r6, mips64r6
Expand Down
2 changes: 1 addition & 1 deletion src/bootstrap/sanity.rs
Original file line number Diff line number Diff line change
Expand Up @@ -206,7 +206,7 @@ than building it.
}

// Make sure musl-root is valid
if target.contains("musl") {
if target.contains("musl") && !target.contains("unikraft") {
// If this is a native target (host is also musl) and no musl-root is given,
// fall back to the system toolchain in /usr before giving up
if build.musl_root(*target).is_none() && build.config.build == *target {
Expand Down
1 change: 1 addition & 0 deletions src/doc/rustc/src/SUMMARY.md
Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,7 @@
- [sparc-unknown-none-elf](./platform-support/sparc-unknown-none-elf.md)
- [*-pc-windows-gnullvm](platform-support/pc-windows-gnullvm.md)
- [\*-nto-qnx-\*](platform-support/nto-qnx.md)
- [*-unikraft-linux-musl](platform-support/unikraft-linux-musl.md)
- [*-unknown-hermit](platform-support/hermit.md)
- [\*-unknown-netbsd\*](platform-support/netbsd.md)
- [*-unknown-openbsd](platform-support/openbsd.md)
Expand Down
1 change: 1 addition & 0 deletions src/doc/rustc/src/platform-support.md
Original file line number Diff line number Diff line change
Expand Up @@ -326,6 +326,7 @@ target | std | host | notes
[`x86_64-pc-windows-gnullvm`](platform-support/pc-windows-gnullvm.md) | ✓ | ✓ |
`x86_64-pc-windows-msvc` | * | | 64-bit Windows XP support
`x86_64-sun-solaris` | ? | | Deprecated target for 64-bit Solaris 10/11, illumos
[`x86_64-unikraft-linux-musl`](platform-support/unikraft-linux-musl.md) | ✓ | | 64-bit Unikraft with musl
`x86_64-unknown-dragonfly` | ✓ | ✓ | 64-bit DragonFlyBSD
`x86_64-unknown-haiku` | ✓ | ✓ | 64-bit Haiku
[`x86_64-unknown-hermit`](platform-support/hermit.md) | ✓ | | x86_64 Hermit
Expand Down
67 changes: 67 additions & 0 deletions src/doc/rustc/src/platform-support/unikraft-linux-musl.md
Original file line number Diff line number Diff line change
@@ -0,0 +1,67 @@
# `*-unikraft-linux-musl`

**Tier: 3**

Targets for the [Unikraft] Unikernel Development Kit (with musl).

[Unikraft]: https://unikraft.org/

Target triplets available so far:

- `x86_64-unikraft-linux-musl`

## Target maintainers

- Martin Kröning ([@mkroening](https://github.com/mkroening))

## Requirements

These targets only support cross-compilation.
The targets do support std.

Unikraft pretends to behave exactly like Linux.
How much of that functionality is available depends on the individual unikernel configuration.
For example, the basic Unikraft + musl config does not support `poll` or networking out of the box.
That functionality requires enabling [`LIBPOSIX_EVENT`] or [lwIP] respectively.

[`LIBPOSIX_EVENT`]: https://github.com/unikraft/unikraft/blob/RELEASE-0.13.1/lib/posix-event/Config.uk
[lwIP]: https://github.com/unikraft/lib-lwip

The Unikraft targets follow Linux's `extern "C"` calling convention.

For these targets, `rustc` does not perform the final linking step.
Instead, the Unikraft build system will produce the final Unikernel image for the selected platform (e.g., KVM, Linux user space, and Xen).

## Building the targets

You can build Rust with support for the targets by adding it to the `target` list in `config.toml`:

```toml
[build]
build-stage = 1
target = [ "x86_64-unikraft-linux-musl" ]
```

## Building Rust programs

Rust does not yet ship pre-compiled artifacts for these targets.
To compile for these targets, you will either need to build Rust with the targets enabled
(see “Building the targets” above), or build your own copy of `core` by using `build-std` or similar.

Linking requires a [KraftKit] shim.
See [unikraft/kraftkit#612] for more information.

[KraftKit]: https://github.com/unikraft/kraftkit
[unikraft/kraftkit#612]: https://github.com/unikraft/kraftkit/issues/612

## Testing

The targets do support running binaries in the form of unikernel images.
How the unikernel image is run depends on the specific platform (e.g., KVM, Linux user space, and Xen).
The targets do not support running the Rust test suite.

## Cross-compilation toolchains and C code

The targets do support C code.
To build compatible C code, you have to use the same compiler and flags as does the Unikraft build system for your specific configuration.
The easiest way to achieve that, is to build the C code with the Unikraft build system when building your unikernel image.
1 change: 1 addition & 0 deletions src/tools/build-manifest/src/main.rs
Original file line number Diff line number Diff line change
Expand Up @@ -148,6 +148,7 @@ static TARGETS: &[&str] = &[
"x86_64-pc-windows-msvc",
"x86_64-sun-solaris",
"x86_64-pc-solaris",
"x86_64-unikraft-linux-musl",
"x86_64-unknown-freebsd",
"x86_64-unknown-illumos",
"x86_64-unknown-linux-gnu",
Expand Down

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