Build rust guests without hyperlight-libc

[ludfjig]

Rust guests transitively depend on hyperlight-libc (picolibc) through hyperlight-guest-bin's default libc feature. The only reason the dependency was needed was an unconditional call to picolibc's srand in generic_init. The Rust guests themselves never use it.

This PR:

• Gates the srand extern and the call in generic_init behind #[cfg(feature = "libc")].
• Sets default-features = false on hyperlight-guest-bin in simpleguest, dummyguest, and witguest

I am also strongly considering making cargo feature libc a non-default cargo feature of hyperlight-guest-bin, since I am guessing most people who write rust guests do not need hyperlight-libc, but would appreciate more thoughts/feedback on that.

Closes #1483

[Copilot]

Pull request overview

This PR reduces Rust guest dependencies by allowing hyperlight-guest-bin to be used without its default libc feature (and therefore without pulling in hyperlight-libc/picolibc) when the guest doesn’t need C/POSIX support.

Changes:

• Gate the srand extern declaration and call in generic_init behind #[cfg(feature = "libc")].
• Update Rust test guests (simpleguest, dummyguest, witguest) to depend on hyperlight-guest-bin with default-features = false (re-enabling only macros where needed).
• Refresh the nested src/tests/rust_guests/Cargo.lock to reflect the reduced dependency graph (dropping hyperlight-libc and its transitive build deps).

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/hyperlight_guest_bin/src/lib.rs	Makes srand usage conditional on the libc feature to avoid requiring picolibc when not needed.
src/tests/rust_guests/simpleguest/Cargo.toml	Disables default features for hyperlight-guest-bin and explicitly enables macros for macro usage.
src/tests/rust_guests/dummyguest/Cargo.toml	Disables default features for hyperlight-guest-bin to avoid transitive hyperlight-libc.
src/tests/rust_guests/witguest/Cargo.toml	Disables default features for hyperlight-guest-bin to avoid transitive hyperlight-libc.
src/tests/rust_guests/Cargo.lock	Updates lockfile to remove hyperlight-libc and related build dependencies from the guest workspace graph.

Comments suppressed due to low confidence (1)

src/hyperlight_guest_bin/src/lib.rs:232

• generic_init renames seed to _seed, but the value is still used when feature = "libc" is enabled. This can trigger the used_underscore_binding warning (and CI runs clippy with -D warnings for hyperlight-guest-bin with --features libc). Prefer keeping the parameter named seed and explicitly marking it as used only in the non-libc configuration.

pub(crate) extern "C" fn generic_init(
    peb_address: u64,
    _seed: u64,
    ops: u64,
    max_log_level: u64,
) -> u64 {
    unsafe {
        GUEST_HANDLE = GuestHandle::init(peb_address as *mut HyperlightPEB);

[andreiltd]

LGTM!