feat(krun): run the library on macOS

The engine is libkrun.1.dylib, dlopen'd from the Homebrew kegs when
the loader's own search fails (bare sonames never reach the brew
prefix); the probe becomes a per-platform hypervisor probe — KVM on
Linux, sysctl + a real hv_vm_create on macOS, so an entitlement
denial (HV_DENIED) names the re-sign fix instead of surfacing as an
opaque krun_start_enter EINVAL. Tool lookup (mke2fs, debugfs) gains
the same keg fallback, and dyld_fallback_dirs() collects the kegs the
bare-soname dlopens (libkrunfw, libarchive) need in
DYLD_FALLBACK_LIBRARY_PATH. The machine child's parent-death contract
moves to a kqueue NOTE_EXIT watcher: macOS has no PR_SET_PDEATHSIG,
and SIGKILL-on-parent-exit is what keeps a killed caller from
stranding a booted machine.

crates/ecrou-cli/src/main.rs

@@ -116,8 +116,15 @@ fn cmd_probe() -> std::process::ExitCode {
 
     let mut ok = true;
 
-    print!("kvm:          ");
-    match krun::kvm_probe() {
+    print!(
+        "{}:      ",
+        if cfg!(target_os = "macos") {
+            "hypervisor"
+        } else {
+            "kvm"
+        }
+    );
+    match krun::hypervisor_probe() {
         Ok(()) => println!("ok"),
         Err(err) => {
             ok = false;
@@ -145,12 +152,20 @@ fn cmd_probe() -> std::process::ExitCode {
     print!("e2fsprogs:    ");
     let mut tools_ok = true;
     for tool in ["mkfs.ext4", "debugfs"] {
-        match std::process::Command::new(tool).arg("-V").output() {
-            Ok(_) => {}
-            Err(err) => {
+        match ecrou::utils::find_tool(tool) {
+            Some(path) => match std::process::Command::new(path).arg("-V").output() {
+                Ok(_) => {}
+                Err(err) => {
+                    ok = false;
+                    tools_ok = false;
+                    println!("{tool} not runnable ({err}); the rootfs image cannot be built");
+                    break;
+                }
+            },
+            None => {
                 ok = false;
                 tools_ok = false;
-                println!("missing {tool} ({err}); the rootfs image cannot be built");
+                println!("missing {tool}; install e2fsprogs, the rootfs image cannot be built");
                 break;
             }
         }

crates/ecrou/src/error.rs

@@ -34,6 +34,7 @@ const KVM_NESTED_HINT: &str = "only actionable on x86_64 hosts";
 
 /// Errors returned by the ecrou library API.
 #[derive(Debug, thiserror::Error)]
+#[allow(clippy::enum_variant_names)] // KvmUnavailable is the platform's word; HvUnavailable is macOS's
 pub enum Error {
     /// No working KVM on this host, and ecrou has no software-emulation
     /// fallback. The remediation names the usual causes in order; the
@@ -49,6 +50,18 @@ pub enum Error {
     )]
     KvmUnavailable(#[source] std::io::Error),
 
+    /// No hardware virtualization on this Mac, and ecrou has no
+    /// software-emulation fallback: libkrun's macOS backend runs on
+    /// the Hypervisor.framework, which means Apple Silicon and
+    /// macOS 14 or newer.
+    #[error(
+        "Hypervisor.framework is not available\n\n\
+         ecrou boots microVMs and needs hardware virtualization:\n\
+         \x20 host:  an Apple Silicon Mac (M1 or later)\n\
+         \x20 os:    macOS 14 or newer"
+    )]
+    HvUnavailable(#[source] std::io::Error),
+
     /// The registry publishes no linux manifest for the requested
     /// architecture; `available` lists the architectures it does serve.
     #[error("No manifest found for architecture '{arch}'. Available: {available}")]
@@ -92,6 +105,19 @@ mod tests {
         assert!(printed.contains("Permission denied"), "{printed}");
     }
 
+    #[cfg(target_os = "macos")]
+    #[test]
+    fn hv_unavailable_renders_remediation() {
+        let msg = Error::HvUnavailable(std::io::Error::other("no hvf")).to_string();
+        assert!(msg.contains("Hypervisor.framework is not available"));
+        assert!(msg.contains("Apple Silicon"));
+        let printed = format!(
+            "{:#}",
+            anyhow::Error::new(Error::HvUnavailable(std::io::Error::other("no hvf")))
+        );
+        assert!(printed.contains("no hvf"), "{printed}");
+    }
+
     #[test]
     fn a_typed_error_survives_the_anyhow_conversion() {
         let raised =

crates/ecrou/src/krun.rs

@@ -1,13 +1,14 @@
 //! Runtime bindings to libkrun's stable C ABI.
 //!
-//! The library (`libkrun.so.1`) loads through dlopen so a missing
-//! install is a remediation message rather than a link error. The
+//! The library (`libkrun.so.1` on Linux, `libkrun.1.dylib` on macOS)
+//! loads through dlopen so a missing install is a remediation message
+//! rather than a link error. The
 //! symbol signatures mirror the `stable-1.19.x` headers; the main
 //! branch is mid-rewrite to a vtable API and is not the target.
 //!
 //! The founding rule holds for this module too: libkrun's VMM runs in
-//! our process and touches only files, sockets, and `/dev/kvm`, all
-//! inside the confinement budget (SPEC.md).
+//! our process and touches only files and sockets (plus `/dev/kvm` on
+//! Linux), all inside the confinement budget (SPEC.md).
 
 use std::ffi::{c_char, CString};
 use std::os::unix::ffi::OsStrExt;
@@ -19,16 +20,41 @@ use crate::Error;
 
 /// The ABI version libkrun reports for a working `/dev/kvm`
 /// (`KVM_GET_API_VERSION`, the first request of the KVMIO range).
+#[cfg(target_os = "linux")]
 const KVM_GET_API_VERSION: libc::c_ulong = 0xAE00;
+#[cfg(target_os = "linux")]
 const KVM_API_VERSION_EXPECTED: libc::c_int = 12;
 
+#[cfg(target_os = "macos")]
+pub const SONAME: &str = "libkrun.1.dylib";
+#[cfg(not(target_os = "macos"))]
 pub const SONAME: &str = "libkrun.so.1";
 
-/// Remediation shown when libkrun cannot be loaded: distro packaging is
-/// still sparse (Fedora carries it; Debian and Ubuntu do not yet).
+/// Remediation shown when libkrun cannot be loaded: on macOS the
+/// official Homebrew tap bottles the library; Linux distro packaging
+/// is still sparse (Fedora carries it; Debian and Ubuntu do not yet).
+#[cfg(target_os = "macos")]
+const LOAD_REMEDIATION: &str = "install it with `brew install libkrun/krun/libkrun`, \
+or point DYLD_LIBRARY_PATH at the directory holding it";
+#[cfg(not(target_os = "macos"))]
 const LOAD_REMEDIATION: &str = "install libkrun, or point LD_LIBRARY_PATH \
 at the directory holding it (a snap stages it next to the binary)";
 
+/// The paths dlopen is tried against, in order. A bare soname relies
+/// on the loader's own search (LD_LIBRARY_PATH on Linux; on macOS it
+/// never reaches the Homebrew prefix, so the keg paths are named).
+fn load_candidates() -> Vec<std::path::PathBuf> {
+    let mut candidates = vec![std::path::PathBuf::from(SONAME)];
+    for prefix in crate::utils::BREW_PREFIXES {
+        candidates.push(
+            std::path::Path::new(prefix)
+                .join("opt/libkrun/lib")
+                .join(SONAME),
+        );
+    }
+    candidates
+}
+
 macro_rules! symbol {
     ($lib:expr, $name:expr, $ty:ty) => {
         symbol!($lib, $name, $ty, "libkrun too old?")
@@ -65,11 +91,24 @@ pub struct Krun {
 impl Krun {
     /// dlopen libkrun, failing with the install remediation.
     pub fn load() -> Result<Self> {
-        // Safety: dlopen of a fixed SONAME; the handle lives in `self`
-        // and every symbol below is used through it.
-        let lib = unsafe { libloading::Library::new(SONAME) }
-            .with_context(|| format!("cannot load {SONAME}: {LOAD_REMEDIATION}"))?;
-        Ok(Krun { lib })
+        let candidates = load_candidates();
+        let mut last: Option<anyhow::Error> = None;
+        for candidate in &candidates {
+            // Safety: dlopen of a fixed name; the handle lives in
+            // `self` and every symbol below is used through it.
+            let lib = unsafe { libloading::Library::new(candidate) };
+            match lib {
+                Ok(lib) => return Ok(Krun { lib }),
+                Err(err) => last = Some(anyhow::Error::new(err)),
+            }
+        }
+        let tried = candidates
+            .iter()
+            .map(|p| p.display().to_string())
+            .collect::<Vec<_>>()
+            .join(", ");
+        Err(last.unwrap_or_else(|| anyhow::anyhow!("no library name to try")))
+            .with_context(|| format!("cannot load {SONAME} (tried {tried}): {LOAD_REMEDIATION}"))
     }
 
     /// `krun_set_log_level`
@@ -327,9 +366,12 @@ fn path_cstring(path: &Path) -> Result<CString> {
         .with_context(|| format!("path contains a NUL: {}", path.display()))
 }
 
-/// Probe KVM the crun way: open `/dev/kvm` read-write, then check
-/// `KVM_GET_API_VERSION` returns 12.
-pub fn kvm_probe() -> Result<()> {
+/// Probe the host hypervisor. On Linux that is KVM: open `/dev/kvm`
+/// read-write, then check `KVM_GET_API_VERSION` returns 12. On macOS
+/// libkrun runs on the Hypervisor.framework, which exists on Apple
+/// Silicon Macs and nothing else.
+#[cfg(target_os = "linux")]
+pub fn hypervisor_probe() -> Result<()> {
     use std::os::unix::io::AsRawFd;
     let file = std::fs::OpenOptions::new()
         .read(true)
@@ -355,10 +397,102 @@ pub fn kvm_probe() -> Result<()> {
     Ok(())
 }
 
+/// The Hypervisor.framework check, in two steps. `sysctl
+/// kern.hv_support` says the machine has the framework; a real
+/// `hv_vm_create` says this process may use it — on current macOS the
+/// entitlement check inside the framework is what kills most
+/// processes, and the denial used to surface only as an opaque
+/// `krun_start_enter` EINVAL after a full image build.
+#[cfg(target_os = "macos")]
+pub fn hypervisor_probe() -> Result<()> {
+    // libkrun's macOS backend is HVF and arm64-only; there is no
+    // build for Intel Macs to probe for.
+    #[cfg(not(target_arch = "aarch64"))]
+    {
+        return Err(anyhow::Error::new(Error::HvUnavailable(
+            std::io::Error::other(
+                "libkrun ships no macOS backend for Intel Macs; an Apple Silicon host is required",
+            ),
+        )));
+    }
+    #[cfg(target_arch = "aarch64")]
+    {
+        let mut supported: libc::c_int = 0;
+        let mut len = std::mem::size_of_val(&supported);
+        // Safety: sysctlbyname with a fixed name and an int-sized
+        // output buffer; the kernel writes only into `supported`.
+        let rc = unsafe {
+            libc::sysctlbyname(
+                c"kern.hv_support".as_ptr(),
+                (&mut supported as *mut libc::c_int).cast(),
+                &mut len,
+                std::ptr::null_mut(),
+                0,
+            )
+        };
+        if rc != 0 {
+            let err = std::io::Error::last_os_error();
+            return Err(anyhow::Error::new(Error::HvUnavailable(err))
+                .context("reading sysctl kern.hv_support"));
+        }
+        if supported != 1 {
+            return Err(anyhow::Error::new(Error::HvUnavailable(
+                std::io::Error::other("this Mac reports no Hypervisor.framework support"),
+            )));
+        }
+        hypervisor_entitlement_probe()
+    }
+}
+
+/// Create and destroy a real framework VM. `HV_DENIED` is the denial
+/// every macOS packaging step has to design around: the framework
+/// grants VM creation only to binaries signed with the
+/// `com.apple.security.hypervisor` entitlement, so the fix is a
+/// re-sign, not a system change. The framework is dlopen'd by
+/// absolute path — ecrou links nothing, and the path is stable across
+/// releases; if it cannot be opened at all, the probe defers to the
+/// engine instead of inventing a verdict.
+#[cfg(target_os = "macos")]
+fn hypervisor_entitlement_probe() -> Result<()> {
+    const HV_DENIED: u32 = 0xfae94007;
+    let framework =
+        std::path::Path::new("/System/Library/Frameworks/Hypervisor.framework/Hypervisor");
+    // Safety: dlopen of a fixed absolute framework path; symbols are
+    // resolved immediately and the handle lives for this function.
+    let lib = match unsafe { libloading::Library::new(framework) } {
+        Ok(lib) => lib,
+        Err(_) => return Ok(()),
+    };
+    let create = symbol!(
+        &lib,
+        b"hv_vm_create\0",
+        unsafe extern "C" fn(*const std::ffi::c_void) -> u32
+    );
+    let destroy = symbol!(&lib, b"hv_vm_destroy\0", unsafe extern "C" fn() -> u32);
+    // Safety: plain calls into the framework; the VM is destroyed
+    // right away, or never created.
+    let ret = unsafe { create(std::ptr::null()) };
+    if ret == 0 {
+        unsafe { destroy() };
+        return Ok(());
+    }
+    let reason = if ret == HV_DENIED {
+        "the framework denied the process (HV_DENIED): sign the binary with the \
+         com.apple.security.hypervisor entitlement, the way packaging does — \
+         `codesign --force --sign - --entitlements <plist> <binary>`"
+    } else {
+        "the framework refused VM creation"
+    };
+    Err(anyhow::Error::new(Error::HvUnavailable(
+        std::io::Error::other(format!("{reason} (hv error 0x{ret:x})")),
+    )))
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
+    #[cfg(target_os = "linux")]
     #[test]
     fn kvm_probe_constant_matches_kvm_abi() {
         // KVMIO base 0xAE; KVM_GET_API_VERSION is the first request.
@@ -366,9 +500,10 @@ mod tests {
         assert_eq!(KVM_API_VERSION_EXPECTED, 12);
     }
 
+    #[cfg(target_os = "linux")]
     #[test]
     fn kvm_probe_reports_unavailability_or_works() {
-        match kvm_probe() {
+        match hypervisor_probe() {
             Ok(()) => {}
             Err(err) => {
                 let msg = format!("{err:#}");
@@ -378,6 +513,21 @@ mod tests {
         }
     }
 
+    #[cfg(target_os = "macos")]
+    #[test]
+    fn hypervisor_probe_reports_unavailability_or_works() {
+        match hypervisor_probe() {
+            Ok(()) => {}
+            Err(err) => {
+                let msg = format!("{err:#}");
+                assert!(
+                    msg.contains("Hypervisor.framework"),
+                    "unhelpful probe error: {msg}"
+                );
+            }
+        }
+    }
+
     #[test]
     fn load_fails_with_remediation_or_round_trips() {
         match Krun::load() {
@@ -389,14 +539,28 @@ mod tests {
             Err(err) => {
                 let msg = format!("{err:#}");
                 assert!(msg.contains(SONAME), "bad load error: {msg}");
-                assert!(
-                    msg.contains("LD_LIBRARY_PATH"),
-                    "remediation missing: {msg}"
-                );
+                // The remediation names the platform's install path:
+                // the loader variable on Linux, the brew tap on macOS.
+                let hint = if cfg!(target_os = "macos") {
+                    "brew install"
+                } else {
+                    "LD_LIBRARY_PATH"
+                };
+                assert!(msg.contains(hint), "remediation missing: {msg}");
             }
         }
     }
 
+    #[test]
+    fn load_candidates_start_with_the_bare_soname() {
+        assert_eq!(load_candidates()[0], std::path::PathBuf::from(SONAME));
+        // The brew keg paths exist only as candidates: dlopen tries
+        // them in order and they are listed even when absent.
+        if cfg!(target_os = "macos") {
+            assert!(load_candidates().len() > 1);
+        }
+    }
+
     #[test]
     fn ptr_array_is_null_terminated() {
         let args = CArgs::build(&["a".to_string(), "b".to_string()]).unwrap();

crates/ecrou/src/lib.rs

@@ -17,9 +17,9 @@
 //! preparation) and [`vm`] (running a command inside a prepared
 //! rootfs). Public functions return [`Result`] carrying the [`Error`]
 //! enum, so consumers can match on host-readiness failures
-//! ([`Error::KvmUnavailable`], [`Error::ArchNotAvailable`]) versus
-//! ordinary failures ([`Error::Other`], which preserves the full context
-//! chain).
+//! ([`Error::KvmUnavailable`], [`Error::HvUnavailable`],
+//! [`Error::ArchNotAvailable`]) versus ordinary failures
+//! ([`Error::Other`], which preserves the full context chain).
 //!
 //! ## Crate split
 //!

crates/ecrou/src/supervise.rs

@@ -10,6 +10,54 @@ use anyhow::{anyhow, Context};
 use crate::krun::Krun;
 use crate::{Error, Result};
 
+/// The macOS stand-in for `prctl(PR_SET_PDEATHSIG)`: a thread in the
+/// child registers a kqueue filter on the parent pid (EVFILT_PROC,
+/// NOTE_EXIT) and kills this process with SIGKILL when the parent
+/// exits. The kernel fires the filter for an already-dead pid's
+/// registration too, and the getppid check catches the window where
+/// the parent died before registration; SIGKILL itself cannot be
+/// caught, which keeps the child's fate identical to Linux's.
+#[cfg(target_os = "macos")]
+fn watch_parent_or_die() {
+    std::thread::spawn(|| {
+        // Safety: kqueue/kevent on self-owned descriptors; the kevent
+        // structs are plain value types the kernel fills in.
+        unsafe {
+            let kq = libc::kqueue();
+            if kq < 0 {
+                return;
+            }
+            let change = libc::kevent {
+                ident: libc::getppid() as usize,
+                filter: libc::EVFILT_PROC,
+                flags: libc::EV_ADD,
+                fflags: libc::NOTE_EXIT,
+                data: 0,
+                udata: std::ptr::null_mut(),
+            };
+            let n = libc::kevent(kq, &change, 1, std::ptr::null_mut(), 0, std::ptr::null());
+            // A failed registration or an orphaned ppid means the
+            // parent is already gone.
+            if n != 0 || libc::getppid() == 1 {
+                libc::kill(libc::getpid(), libc::SIGKILL);
+            }
+            let mut event: libc::kevent = std::mem::zeroed();
+            loop {
+                let n = libc::kevent(kq, std::ptr::null(), 0, &mut event, 1, std::ptr::null());
+                if n > 0 {
+                    break;
+                }
+                if n < 0
+                    && std::io::Error::last_os_error().kind() != std::io::ErrorKind::Interrupted
+                {
+                    break;
+                }
+            }
+            libc::kill(libc::getpid(), libc::SIGKILL);
+        }
+    });
+}
+
 /// Fork the machine process and enter the VM loop inside it. The
 /// child only touches libkrun configuration before entering the VM
 /// loop, which never returns: a normal payload exit ends the child
@@ -23,7 +71,7 @@ pub(crate) fn spawn_machine(
     let child = unsafe { libc::fork() };
     if child == 0 {
         // Safety: after fork the child runs no threads of its own; the
-        // prctl/exit pair has no unwinding preconditions.
+        // kill/exit pair has no unwinding preconditions.
         let bail = |msg: String, code: i32| -> ! {
             // The console file is the channel the parent streams: a
             // boot failure belongs in it, next to whatever the guest
@@ -37,15 +85,24 @@ pub(crate) fn spawn_machine(
             eprintln!("Error: {msg}");
             unsafe { libc::_exit(code) }
         };
+        // The parent-death contract, per platform: Linux delivers
+        // SIGKILL through PR_SET_PDEATHSIG; macOS has no prctl, so
+        // a watcher thread follows the parent through a kqueue and
+        // kills this process when the parent goes away.
+        #[cfg(target_os = "linux")]
         unsafe {
             libc::prctl(libc::PR_SET_PDEATHSIG, libc::SIGKILL);
-            // Headless only: unwire the console input (with a tty on
-            // fd 0 libkrun puts that terminal into raw mode, which
-            // fights whoever owns it, and stops a background caller
-            // with SIGTTOU). /dev/null keeps the console on its plain
-            // path and still forwards a Ctrl-C sent to the process
-            // group into the guest. An interactive machine wants the
-            // opposite: fd 0 is its console input by design.
+        }
+        #[cfg(target_os = "macos")]
+        watch_parent_or_die();
+        // Headless only: unwire the console input (with a tty on
+        // fd 0 libkrun puts that terminal into raw mode, which
+        // fights whoever owns it, and stops a background caller
+        // with SIGTTOU). /dev/null keeps the console on its plain
+        // path and still forwards a Ctrl-C sent to the process
+        // group into the guest. An interactive machine wants the
+        // opposite: fd 0 is its console input by design.
+        unsafe {
             if !interactive {
                 let null = libc::open(c"/dev/null".as_ptr(), libc::O_RDWR);
                 if null >= 0 {

crates/ecrou/src/utils.rs

@@ -160,6 +160,125 @@ pub fn map_oci_arch(arch: &str) -> String {
     Arch::from_str(arch).oci_name().to_string()
 }
 
+// ============================================================================
+// External tool lookup
+// ============================================================================
+
+/// The Homebrew prefixes the lookup falls back to. Empty off macOS:
+/// Homebrew does not exist there and PATH is the whole story.
+#[cfg(target_os = "macos")]
+pub const BREW_PREFIXES: &[&str] = &["/opt/homebrew", "/usr/local"];
+#[cfg(not(target_os = "macos"))]
+pub const BREW_PREFIXES: &[&str] = &[];
+
+/// The keg-only formulae the run's external tools come from, in the
+/// order they should be preferred. e2fsprogs is keg-only in Homebrew
+/// (its sbin never reaches PATH), and the tap ships its own variant
+/// built with libarchive, which outranks the core bottle.
+#[cfg(target_os = "macos")]
+const BREW_TOOL_FORMULAE: &[&str] = &["e2fsprogs-libarchive", "e2fsprogs"];
+#[cfg(not(target_os = "macos"))]
+const BREW_TOOL_FORMULAE: &[&str] = &[];
+
+/// Locate an external tool the run shells out to: PATH first, then
+/// the Homebrew keg directories. Returns the path, so callers spawn a
+/// deterministic binary instead of a whatever-came-first `Command`.
+pub fn find_tool(name: &str) -> Option<PathBuf> {
+    if let Some(paths) = std::env::var_os("PATH") {
+        for dir in std::env::split_paths(&paths) {
+            let candidate = dir.join(name);
+            if is_executable(&candidate) {
+                return Some(candidate);
+            }
+        }
+    }
+    for prefix in BREW_PREFIXES {
+        for formula in BREW_TOOL_FORMULAE {
+            for sub in ["sbin", "bin"] {
+                let candidate = Path::new(prefix)
+                    .join("opt")
+                    .join(formula)
+                    .join(sub)
+                    .join(name);
+                if is_executable(&candidate) {
+                    return Some(candidate);
+                }
+            }
+        }
+    }
+    None
+}
+
+fn is_executable(path: &Path) -> bool {
+    use std::os::unix::fs::PermissionsExt;
+    std::fs::metadata(path)
+        .map(|m| m.is_file() && m.permissions().mode() & 0o111 != 0)
+        .unwrap_or(false)
+}
+
+/// The brew kegs whose dylibs are loaded by bare soname at runtime:
+/// libkrunfw (loaded by libkrun) and libarchive (loaded by a
+/// libarchive-capable mke2fs). dyld's fallback search never reaches
+/// the brew prefix, so these directories have to land in
+/// DYLD_FALLBACK_LIBRARY_PATH before any of those loads happen.
+#[cfg(target_os = "macos")]
+const DYLD_KEGS: &[&str] = &["libkrunfw", "libarchive"];
+#[cfg(not(target_os = "macos"))]
+const DYLD_KEGS: &[&str] = &[];
+
+/// Directories the libarchive dylib can be dlopen'd from, joined for
+/// DYLD_FALLBACK_LIBRARY_PATH. Superseded by dyld_fallback_dirs; kept
+/// only until the image builder stops calling it.
+#[cfg(target_os = "macos")]
+pub fn libarchive_fallback_dirs() -> Option<String> {
+    let mut dirs = Vec::new();
+    for prefix in BREW_PREFIXES {
+        let dir = Path::new(prefix).join("opt/libarchive/lib");
+        if dir.is_dir() {
+            dirs.push(dir.as_os_str().to_os_string());
+        }
+    }
+    if dirs.is_empty() {
+        None
+    } else {
+        Some(
+            std::env::join_paths(dirs)
+                .ok()?
+                .to_string_lossy()
+                .into_owned(),
+        )
+    }
+}
+
+#[cfg(not(target_os = "macos"))]
+pub fn libarchive_fallback_dirs() -> Option<String> {
+    None
+}
+
+/// Directories the bare-soname dlopens can be satisfied from, joined
+/// for DYLD_FALLBACK_LIBRARY_PATH, or None when none of them exists.
+pub fn dyld_fallback_dirs() -> Option<String> {
+    let mut dirs = Vec::new();
+    for prefix in BREW_PREFIXES {
+        for keg in DYLD_KEGS {
+            let dir = Path::new(prefix).join("opt").join(keg).join("lib");
+            if dir.is_dir() {
+                dirs.push(dir.into_os_string());
+            }
+        }
+    }
+    if dirs.is_empty() {
+        None
+    } else {
+        Some(
+            std::env::join_paths(dirs)
+                .ok()?
+                .to_string_lossy()
+                .into_owned(),
+        )
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/ecrou/src/vm.rs

@@ -2,7 +2,7 @@
 //! payload with live stdio, propagate its exit code, throw the machine
 //! away.
 //!
-//! The flow is: KVM probe, rootfs prepare (cache-aware download and
+//! The flow is: hypervisor probe, rootfs prepare (cache-aware download and
 //! extraction), guest init written into the scratch rootfs, libkrun
 //! context wired to it, `krun_start_enter` blocking on this thread, then
 //! the control file read back for the exit code. The VMM runs inside
@@ -142,7 +142,7 @@ pub fn run_prepared(rootfs: &PreparedRootfs, options: &RunOptions) -> Result<i32
         }
     }
 
-    krun::kvm_probe()?;
+    krun::hypervisor_probe()?;
     let krun = Krun::load()?;
 
     let ram_mib = parse_memory_mib(&options.memory).map_err(Error::Other)?;