fix(release): pin the tap formula to the release tarball

The formula's url pointed at the tag's source archive while its
sha256 came from the darwin tarball — two files, one checksum, so
brew refused every install. The formula now pours the darwin tarball
itself: the release workflow attaches it to the GitHub release, the
tap formula pins that asset's real sha256, and installs stop
compiling rust (the CI-signed entitlement also survives, which a
source build would have stripped).

.github/workflows/ci.yml

@@ -38,6 +38,60 @@ jobs:
       - name: cargo test
         run: cargo test
 
+  macos:
+    name: macos — fmt, clippy, test, probe
+    runs-on: macos-26
+    timeout-minutes: 45
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: clippy, rustfmt
+
+      - uses: Swatinem/rust-cache@v2
+
+      # Homebrew refuses formulae from third-party taps until the tap
+      # is trusted once; libkrun's dependencies come from the krun tap.
+      - name: Trust the krun tap
+        run: brew trust --tap libkrun/krun
+
+      # The engine is dlopen'd from the brew kegs at runtime; e2fsprogs
+      # supplies mke2fs and libarchive its tar path.
+      - name: Install the engine and the image tooling
+        run: brew install libkrun/homebrew-krun/libkrun e2fsprogs libarchive
+
+      - name: cargo fmt
+        run: cargo fmt --all -- --check
+
+      - name: cargo clippy
+        run: cargo clippy --all-targets -- -D warnings
+
+      - name: cargo test
+        run: cargo test
+
+      - name: Build the CLI
+        run: cargo build --release -p ecrou-cli
+
+      # HVF grants VM creation only to binaries carrying the hypervisor
+      # entitlement on current macOS; packaging signs the same way.
+      - name: Sign the binary with the hypervisor entitlement
+        run: codesign --force --sign - --entitlements packaging/homebrew/ecrou.entitlements target/release/ecrou
+
+      # GitHub's macOS runners expose no Hypervisor.framework (they run
+      # without nested virtualization), so nothing boots here — the
+      # boot e2e lives on Linux (the snap e2e) and on real Macs. The
+      # probe must still behave: the engine loads from the krun tap,
+      # the tools are found, and the HVF absence is reported as that.
+      - name: Probe
+        run: |
+          set -euo pipefail
+          out="$(./target/release/ecrou probe || true)"
+          printf '%s\n' "$out"
+          grep -q "libkrun:      ok" <<<"$out"
+          grep -q "e2fsprogs:    ok" <<<"$out"
+          grep -q "no Hypervisor.framework support" <<<"$out"
+
   t6:
     name: T6 strace audit
     runs-on: ubuntu-latest

.github/workflows/release.yml

@@ -62,6 +62,121 @@ jobs:
           name: ${{ matrix.artifact }}
           path: ${{ steps.build.outputs.snap }}
 
+  # The macos distribution is a signed tarball, not a store release:
+  # brew taps install from it, and the entitlement signature rides in
+  # the artifact.
+  build-macos:
+    needs: gate
+    if: needs.gate.outputs.release == 'true'
+    runs-on: macos-26
+    timeout-minutes: 45
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: dtolnay/rust-toolchain@stable
+
+      - uses: Swatinem/rust-cache@v2
+
+      - name: Stamp the tag version into the manifests
+        run: |
+          v="${GITHUB_REF_NAME#v}"
+          sed -i '' "s/^version = \".*\"/version = \"$v\"/" Cargo.toml
+          grep -H '^version' Cargo.toml
+
+      - name: Build the CLI
+        run: cargo build --release -p ecrou-cli
+
+      - name: Sign the binary with the hypervisor entitlement
+        run: codesign --force --sign - --entitlements packaging/homebrew/ecrou.entitlements target/release/ecrou
+
+      - name: Package
+        run: |
+          v="${GITHUB_REF_NAME#v}"
+          tar -czf "ecrou-v$v-darwin-arm64.tar.gz" -C target/release ecrou
+          shasum -a 256 "ecrou-v$v-darwin-arm64.tar.gz" > "ecrou-v$v-darwin-arm64.tar.gz.sha256"
+          mkdir dist && mv ecrou-v$v-darwin-* dist/
+
+      - uses: actions/upload-artifact@v4
+        with:
+          name: ecrou-darwin-arm64
+          path: dist/*
+
+  # The tap repo (vhaudiquet/homebrew-ecrou) is a publish target, not
+  # the source of truth: the formula is maintained in packaging/ and
+  # this job rewrites its url/sha256 for the release tarball (the
+  # binary publish-release just attached) and pushes it. Needs a PAT with push access to the tap repo as the
+  # HOMEBREW_TAP_TOKEN secret; without it the job is a no-op so tags
+  # still release.
+  # The Homebrew formula pours this tarball, so it has to be attached
+  # to the release before the tap update runs.
+  publish-release:
+    needs: build-macos
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/download-artifact@v4
+        with:
+          name: ecrou-darwin-arm64
+          path: dist
+
+      - name: Create the release and upload the tarball
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          set -euo pipefail
+          v="${GITHUB_REF_NAME#v}"
+          gh release create "v$v" --title "ecrou $v" --generate-notes || true
+          gh release upload "v$v" dist/* --clobber
+
+  update-homebrew:
+    needs: publish-release
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/download-artifact@v4
+        with:
+          name: ecrou-darwin-arm64
+          path: dist
+
+      - name: Push the formula to the tap
+        env:
+          TAP_TOKEN: ${{ secrets.HOMEBREW_TAP_TOKEN }}
+        run: |
+          set -euo pipefail
+          if [[ -z "$TAP_TOKEN" ]]; then
+            echo "::notice::no HOMEBREW_TAP_TOKEN secret set; tap not updated"
+            exit 0
+          fi
+          v="${GITHUB_REF_NAME#v}"
+          sha="$(cut -d' ' -f1 "dist/ecrou-v$v-darwin-arm64.tar.gz.sha256")"
+          url="https://github.com/vhaudiquet/ecrou/releases/download/v$v/ecrou-v$v-darwin-arm64.tar.gz"
+          mkdir -p formula/Formula
+          sed -e '/^  # Placeholder pin:/d' -e "s|^  url \"https://github.com/vhaudiquet/ecrou.git\", tag: \"v[0-9][0-9.]*\"$|  url \"$url\"\n  sha256 \"$sha\"|" packaging/homebrew/Formula/ecrou.rb > formula/Formula/ecrou.rb
+          grep -q "sha256 \"$sha\"" formula/Formula/ecrou.rb
+          # A missing tap repo skips with a notice; a token that
+          # cannot clone an existing repo still fails the job.
+          code="$(curl -s -o /dev/null -w '%{http_code}' \
+            -H "Authorization: Bearer $TAP_TOKEN" \
+            https://api.github.com/repos/vhaudiquet/homebrew-ecrou)"
+          if [[ "$code" != "200" ]]; then
+            echo "::notice::vhaudiquet/homebrew-ecrou unreachable (HTTP $code); tap not updated"
+            exit 0
+          fi
+          git clone -q "https://x-access-token:$TAP_TOKEN@github.com/vhaudiquet/homebrew-ecrou" tap
+          mkdir -p tap/Formula
+          cp formula/Formula/ecrou.rb tap/Formula/ecrou.rb
+          cd tap
+          git add Formula/ecrou.rb
+          git -c user.name="ecrou-release" -c user.email="noreply@github.com" \
+            commit -m "ecrou $v"
+          git push -q origin HEAD:main
+
   publish-snap:
     needs: build-snap
     runs-on: ubuntu-latest

Cargo.lock

@@ -385,6 +385,7 @@ dependencies = [
  "clap",
  "ecrou",
  "indicatif",
+ "libc",
  "log",
 ]
 

README.md

@@ -8,12 +8,18 @@
 
 ### Installation
 
-ecrou is available as a strictly confined snap:
+Linux (strictly confined snap, KVM required):
 ```
 sudo snap install ecrou
 sudo snap connect ecrou:kvm
 ```
 
+macOS (Apple Silicon, Homebrew):
+```
+brew trust --tap libkrun/krun
+brew install vhaudiquet/ecrou/ecrou
+```
+
 ### Usage
 
 ```

SPEC.md

@@ -34,9 +34,11 @@ and fails with a remediation message naming the install when it is
 missing; nothing links at build time, and the snap bundles the library
 plus libkrunfw next to itself.
 
-KVM is required; there is no TCG fallback. A machine without working
+KVM is required on Linux, Hypervisor.framework on macOS; there is no
-KVM is `Error::KvmUnavailable` with the remediation text, and `ecrou
+TCG fallback. A machine without working KVM is `Error::KvmUnavailable`
-probe` reports it before any run. The VMM runs inside the machine
+with the remediation text, and `ecrou probe` reports it before any
+run (on macOS the probe goes further: it checks the hypervisor
+entitlement too, see the macOS section). The VMM runs inside the machine
 child, not on the caller's thread (see Cancellation).
 
 libkrun's mapped-volumes entry point is explicitly unsupported on
@@ -282,6 +284,82 @@ stop:
   point: 24 s end to end, boot and apt included, cache-warm (snap
   0.1.0 engine, October 2026).
 
+## macOS
+
+The same ABI, a different substrate. The engine is dlopen'd from the
+Homebrew kegs (`libkrun` from the `libkrun/homebrew-krun` tap, which
+builds the HVF backend and links Hypervisor.framework); the keg path
+is a search fallback, not a hard-coded prefix, and the run fails with
+a remediation naming the tap when the library is absent. macOS needs
+no snap: no store sandbox, no staged libraries — Homebrew's prefix is
+the distribution channel. There is no riscv64 or amd64 build; libkrun
+supports Hypervisor.framework on arm64 only.
+
+Two macOS facts shape the code:
+
+**Bare-soname dlopens.** The engine loads `libkrunfw.5.dylib` by bare
+soname at `krun_start_enter`, and a libarchive-capable `mke2fs` loads
+`libarchive.13.dylib` the same way. dyld never searches the brew
+prefix, and it reads `DYLD_FALLBACK_LIBRARY_PATH` once, at process
+startup — a setenv afterwards is invisible to it. The CLI therefore
+re-execs itself (exec restarts dyld) when the variable is unset and
+the kegs exist; library consumers must set the variable themselves
+before their process starts. mkfs children are exec'd fresh, so the
+per-spawn env in image.rs works regardless.
+
+**The hypervisor entitlement.** Hypervisor.framework grants VM
+creation only to binaries signed with the
+`com.apple.security.hypervisor` entitlement — current macOS enforces
+this for ad-hoc-signed binaries too, where older releases granted the
+framework implicitly. The denial surfaces as `hv_vm_create` returning
+`HV_DENIED` (0xfae94007), which without a probe showed up only as an
+opaque `krun_start_enter` EINVAL after a full image build. `probe` now
+creates and destroys a real framework VM (dlopen'd, no link-time
+dependency) so the denial is reported with the re-sign remediation
+before any image work. Packaging signs at install (the Homebrew
+formula, the same pattern krunkit's formula carries, and the release
+tarball's codesign step); a `cargo build` developer re-signs after
+each build, per the README snippet.
+
+The ext4 image is built the same way as on Linux, with one fallback:
+when the found `mke2fs` cannot populate from a tarball (Homebrew's
+e2fsprogs bottle builds without libarchive), the image builder
+unpacks the rootfs to a tree and lets mke2fs populate from the
+directory — slower, and run states it in the log. The T6 strace audit
+and the `/dev/kvm` gating stay Linux-only: strace does not exist on
+macOS and the hypervisor gate is the entitlement probe instead. CI
+runs the whole gate on a `macos-26` runner; hosted macOS runners
+expose no Hypervisor.framework, so the boot e2e is the Linux snap
+e2e and any real Mac — CI only asserts that the probe loads the
+engine from the krun tap and reports the HVF absence. The release
+workflow ships a signed darwin-arm64 tarball (build and sign only,
+no boot).
+
+## Homebrew
+
+`packaging/homebrew/Formula/ecrou.rb` installs into a
+`vhaudiquet/homebrew-ecrou` tap — the repo name is what makes
+`brew install vhaudiquet/ecrou/ecrou` resolve without an explicit
+`brew tap`. The formula pours the darwin tarball the release
+workflow signs and attaches to the GitHub release: no local compile,
+and the entitlement signature survives, which a rebuild here would
+strip. The tap repo is a publish target, not the source of
+truth: the release workflow rewrites the formula's url/sha256 for
+the release tarball and pushes it (gated on a `HOMEBREW_TAP_TOKEN`
+PAT; without the secret the job no-ops). The formula carries the runtime
+dependencies (`libkrun` from the krun tap, `e2fsprogs`, `libarchive`),
+builds from source with cargo, and re-signs the binary with the
+entitlements plist from `packaging/homebrew/` — brew bottles are
+ad-hoc signed, so the signature is part of the formula's install,
+not of the artifact. The in-repo formula's tag pin is a placeholder:
+the release workflow rewrites url and sha256 (of the release asset,
+not the source archive — they are different files) when it pushes
+the formula to the tap. Homebrew's tap-trust gate refuses dependencies
+from third-party taps until their tap is trusted, so the README
+leads with `brew trust --tap libkrun/krun` and CI trusts the tap
+before its install; removing that tax is another argument for
+libkrun landing in homebrew-core.
+
 ## Snap packaging
 
 Confinement: strict. Plugs: `network`, `home`, `kvm`. The manual

crates/ecrou-cli/Cargo.toml

@@ -12,6 +12,7 @@ name = "ecrou"
 path = "src/main.rs"
 
 [dependencies]
+libc = "0.2"
 ecrou = { path = "../ecrou" }
 
 # CLI parsing

crates/ecrou-cli/src/main.rs

@@ -16,6 +16,7 @@ use cli::{parse_env, parse_volume, Cli, Command, RunArgs};
 use progress::TermProgress;
 
 fn main() -> std::process::ExitCode {
+    reexec_with_dyld_fallback();
     let cli = Cli::parse();
     logger::init(cli.verbose);
     match cli.command {
@@ -25,6 +26,67 @@ fn main() -> std::process::ExitCode {
     }
 }
 
+/// The engine's dlopen of libkrunfw and mke2fs's dlopen of libarchive
+/// both name bare sonames, and dyld reads DYLD_FALLBACK_LIBRARY_PATH
+/// only once, at process startup — a setenv afterwards is invisible to
+/// it. When the variable is unset and the brew kegs exist, re-exec:
+/// exec restarts dyld, which reads the variable fresh. Library
+/// consumers instead set the variable themselves before their process
+/// starts (SPEC.md, macOS).
+#[cfg(target_os = "macos")]
+fn reexec_with_dyld_fallback() {
+    use std::os::unix::ffi::{OsStrExt as _, OsStringExt};
+
+    if std::env::var_os("DYLD_FALLBACK_LIBRARY_PATH").is_some() {
+        return;
+    }
+    let dirs = match ecrou::utils::dyld_fallback_dirs() {
+        Some(dirs) => dirs,
+        None => return,
+    };
+    std::env::set_var("DYLD_FALLBACK_LIBRARY_PATH", &dirs);
+    let program = match std::env::current_exe() {
+        Ok(path) => path,
+        Err(_) => return,
+    };
+    let mut argv: Vec<std::ffi::CString> = Vec::new();
+    let name = program
+        .file_name()
+        .map(|n| n.to_owned())
+        .unwrap_or_default();
+    argv.push(match std::ffi::CString::new(name.into_vec()) {
+        Ok(name) => name,
+        Err(_) => return,
+    });
+    let program = match std::ffi::CString::new(program.as_os_str().as_bytes()) {
+        Ok(program) => program,
+        Err(_) => return,
+    };
+    for arg in std::env::args_os().skip(1) {
+        match std::ffi::CString::new(arg.into_vec()) {
+            Ok(arg) => argv.push(arg),
+            // An argument with interior NULs cannot cross execv at
+            // all; the original process would have failed the same
+            // way, so bail out of the re-exec quietly.
+            Err(_) => return,
+        }
+    }
+    // Safety: execv replaces this process with itself, same program;
+    // on failure the process keeps running exactly as before.
+    // execv takes a C array of pointers into the strings, NUL-ended;
+    // the CStrings stay alive in `strings` across the call.
+    let mut pointers: Vec<*const libc::c_char> = argv.iter().map(|s| s.as_ptr().cast()).collect();
+    pointers.push(std::ptr::null());
+    // Safety: execv replaces this process with itself, same program;
+    // on failure the process keeps running exactly as before.
+    unsafe {
+        libc::execv(program.as_ptr().cast(), pointers.as_ptr());
+    }
+}
+
+#[cfg(not(target_os = "macos"))]
+fn reexec_with_dyld_fallback() {}
+
 fn cmd_run(args: &RunArgs, cli_verbose: bool) -> std::process::ExitCode {
     // A tty drives the payload's output through the terminal while the
     // capture share points the same streams at files: one of them has
@@ -116,8 +178,15 @@ fn cmd_probe() -> std::process::ExitCode {
 
     let mut ok = true;
 
-    print!("kvm:          ");
+    print!(
-    match krun::kvm_probe() {
+        "{}:      ",
+        if cfg!(target_os = "macos") {
+            "hypervisor"
+        } else {
+            "kvm"
+        }
+    );
+    match krun::hypervisor_probe() {
         Ok(()) => println!("ok"),
         Err(err) => {
             ok = false;
@@ -145,12 +214,20 @@ 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() {
+        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!("missing {tool} ({err}); the rootfs image cannot be built");
+                    println!("{tool} not runnable ({err}); the rootfs image cannot be built");
+                    break;
+                }
+            },
+            None => {
+                ok = false;
+                tools_ok = false;
+                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/image.rs

@@ -9,6 +9,14 @@
 //! lose them. An unprivileged extract cannot preserve a tar's owners
 //! (chown to an arbitrary uid is root's alone); a tarball to image
 //! pipeline never needs one.
+//!
+//! Tarball populate is a build-time choice in e2fsprogs: compiled in,
+//! it loads libarchive by dlopen at runtime (`libarchive.so.13` on
+//! Linux, `libarchive.13.dylib` on macOS), so presence cannot be
+//! assumed from the binary. A build without it (Homebrew's bottle, for
+//! one) gets the tree-populate fallback: the tarball is unpacked and
+//! mke2fs copies the directory, which loses the tar owners — flagged
+//! through the progress channel, never silently.
 
 use std::path::{Path, PathBuf};
 use std::process::Command;
@@ -17,6 +25,16 @@ use anyhow::{anyhow, Context};
 
 use crate::progress::Progress;
 
+/// Appended to a mkfs failure whose stderr names libarchive: the
+/// tarball populate loads it by dlopen at runtime, and the message
+/// names the platform's way to get the dylib in place.
+#[cfg(target_os = "macos")]
+const LIBARCHIVE_REMEDIATION: &str = "; the populate step loads libarchive \
+by dlopen at runtime, and `brew install libarchive` provides the dylib";
+#[cfg(not(target_os = "macos"))]
+const LIBARCHIVE_REMEDIATION: &str = "; the populate step loads libarchive \
+at runtime (the snap stages libarchive13 next to the binary)";
+
 /// Build the rootfs image at `image` from `tarball`.
 ///
 /// An OCI layer bundle merges into one plain tar first, so the whiteout
@@ -41,7 +59,7 @@ pub(crate) fn build_rootfs_image(
         }
     }
     let source: &Path = merged.as_deref().unwrap_or(tarball);
-    let result = mkfs_from_tar(source, image);
+    let result = mkfs_from_tar(source, image, progress);
     if let Some(side) = merged {
         // The merged archive has value only until mke2fs consumes it;
         // a failure to clean up must not mask mkfs's own error.
@@ -71,7 +89,7 @@ pub(crate) fn looks_like_ext4(image: &Path) -> bool {
 /// Build the entry image: mke2fs consumes the archive (merged first
 /// when the tarball is an OCI layer bundle) and the result publishes
 /// atomically.
-fn mkfs_from_tar(tarball: &Path, image: &Path) -> anyhow::Result<()> {
+fn mkfs_from_tar(tarball: &Path, image: &Path, progress: &dyn Progress) -> anyhow::Result<()> {
     // The build lands in a sibling file first and renames over the
     // image only on success. mke2fs creates and sizes the file before
     // it populates, so a failed build would otherwise leave a
@@ -79,7 +97,7 @@ fn mkfs_from_tar(tarball: &Path, image: &Path) -> anyhow::Result<()> {
     // than the tarball it came from, and trusted by the freshness
     // check forever after.
     let staging = image.with_extension("part");
-    let built = build_ext4(tarball, &staging);
+    let built = build_ext4(tarball, &staging, progress);
     if built.is_ok() {
         std::fs::rename(&staging, image)
             .with_context(|| format!("publishing {}", image.display()))?;
@@ -89,10 +107,75 @@ fn mkfs_from_tar(tarball: &Path, image: &Path) -> anyhow::Result<()> {
     built
 }
 
+/// Whether the system mke2fs populates straight from a tarball. The
+/// support is compiled in or out (and dlopen'd at runtime when in), so
+/// the only honest probe is the real tool over a minimal archive:
+/// build a four-MiB image from a one-entry tarball once per process
+/// and cache the verdict.
+fn mke2fs_reads_tarballs() -> bool {
+    static VERDICT: std::sync::OnceLock<bool> = std::sync::OnceLock::new();
+    *VERDICT.get_or_init(|| {
+        let scratch = match tempfile::tempdir() {
+            Ok(dir) => dir,
+            Err(_) => return false,
+        };
+        let tarball = scratch.path().join("probe.tar");
+        let file = match std::fs::File::create(&tarball) {
+            Ok(file) => file,
+            Err(_) => return false,
+        };
+        let mut builder = tar::Builder::new(file);
+        let mut header = tar::Header::new_gnu();
+        header.set_size(0);
+        header.set_mode(0o755);
+        header.set_entry_type(tar::EntryType::Regular);
+        if builder
+            .append_data(&mut header, "probe", std::io::empty())
+            .is_err()
+        {
+            return false;
+        }
+        let image = scratch.path().join("probe.ext4");
+        if std::fs::File::create(&image)
+            .and_then(|f| f.set_len(4 * 1024 * 1024))
+            .is_err()
+        {
+            return false;
+        }
+        match mkfs_tool() {
+            Some(mut cmd) => cmd
+                .args(["-q", "-F", "-N", "16", "-d"])
+                .arg(&tarball)
+                .arg(&image)
+                .output()
+                .map(|out| out.status.success())
+                .unwrap_or(false),
+            None => false,
+        }
+    })
+}
+
+/// The mke2fs command, resolved through the tool lookup and, on macOS,
+/// pointed at the directories a dlopen'd libarchive can live in.
+fn mkfs_tool() -> Option<std::process::Command> {
+    let mut cmd = Command::new(crate::utils::find_tool("mkfs.ext4")?);
+    // The child execs fresh, so it reads the variable at startup even
+    // when the parent process itself never had it.
+    if let Some(dirs) = crate::utils::dyld_fallback_dirs() {
+        cmd.env("DYLD_FALLBACK_LIBRARY_PATH", dirs);
+    }
+    Some(cmd)
+}
+
+/// The debugfs command, resolved through the tool lookup.
+fn debugfs_tool() -> Option<Command> {
+    crate::utils::find_tool("debugfs").map(Command::new)
+}
+
 /// Create `image`, size it from a scan of the archive, and run mke2fs
 /// over it. The filesystem size and inode count come from the scan:
 /// mke2fs derives neither from a tar.
-fn build_ext4(tarball: &Path, image: &Path) -> anyhow::Result<()> {
+fn build_ext4(tarball: &Path, image: &Path, progress: &dyn Progress) -> anyhow::Result<()> {
     let (bytes, entries) = tar_scan(tarball)?;
     // Headroom for the journal, the inode tables and block rounding.
     // The file is created sparse, so generous headroom costs nothing
@@ -115,16 +198,44 @@ fn build_ext4(tarball: &Path, image: &Path) -> anyhow::Result<()> {
         .with_context(|| format!("sizing {}", image.display()))?;
     drop(file);
 
-    let out = Command::new("mkfs.ext4")
+    // Tarball populate when the tool can, tree populate when it
+    // cannot: the fallback loses the tar's owners (every entry takes
+    // the invoking user's), which is said out loud, not swallowed.
+    let extracted: Option<PathBuf> = if mke2fs_reads_tarballs() {
+        None
+    } else {
+        let dir = image.with_extension("populate");
+        std::fs::create_dir_all(&dir).with_context(|| format!("creating {}", dir.display()))?;
+        crate::extract::tar_decoder(tarball)?
+            .unpack(&dir)
+            .with_context(|| format!("unpacking {} into {}", tarball.display(), dir.display()))?;
+        progress.message(
+            "this mke2fs cannot read tarballs (no libarchive); populating \
+             from the extracted tree, so tar owners are lost",
+        );
+        Some(dir)
+    };
+    let populate: &Path = extracted.as_deref().unwrap_or(tarball);
+    let out = mkfs_tool()
+        .ok_or_else(|| anyhow!("mkfs.ext4 not found: install e2fsprogs"))?
         .args(["-q", "-F", "-N", &inodes.to_string(), "-d"])
-        .arg(tarball)
+        .arg(populate)
         .arg(image)
         .output()
-        .map_err(|e| anyhow!("mkfs.ext4 not found ({e}): install e2fsprogs; the snap stages it"))?;
+        .map_err(|e| anyhow!("mkfs.ext4 not runnable ({e}): install e2fsprogs"))?;
+    if let Some(dir) = extracted {
+        // A failure to clean the tree must not mask mkfs's own verdict.
+        let _ = std::fs::remove_dir_all(dir);
+    }
     if !out.status.success() {
+        let stderr = String::from_utf8_lossy(&out.stderr).trim().to_string();
+        let note = if stderr.contains("libarchive") {
+            LIBARCHIVE_REMEDIATION
+        } else {
+            ""
+        };
         return Err(anyhow!(
-            "mkfs.ext4 failed building the rootfs image: {}",
+            "mkfs.ext4 failed building the rootfs image: {stderr}{note}"
-            String::from_utf8_lossy(&out.stderr).trim()
         ));
     }
     Ok(())
@@ -143,10 +254,20 @@ fn tar_scan(tarball: &Path) -> anyhow::Result<(u64, u64)> {
     Ok((bytes, entries))
 }
 
-/// Copy the cache entry image into the scratch directory. cp reflinks
+/// Copy the cache entry image into the scratch directory. On Linux cp
-/// where the filesystem has them and keeps the copy sparse either way:
+/// reflinks where the filesystem has them and keeps the copy sparse;
-/// an image occupying 400 MiB must not materialize a GiB of holes.
+/// an image occupying 400 MiB must not materialize a GiB of holes. On
+/// macOS APFS clones the file at the block level through fclonefileat,
+/// which std::fs::copy drives (and a cross-volume copy falls back to a
+/// plain read/write).
 pub(crate) fn copy_image(src: &Path, dst: &Path) -> anyhow::Result<()> {
+    #[cfg(target_os = "macos")]
+    {
+        std::fs::copy(src, dst)
+            .with_context(|| format!("copying {} to {}", src.display(), dst.display()))?;
+    }
+    #[cfg(not(target_os = "macos"))]
+    {
         let out = Command::new("cp")
             .args(["--reflink=auto", "--sparse=auto"])
             .arg(src)
@@ -159,6 +280,7 @@ pub(crate) fn copy_image(src: &Path, dst: &Path) -> anyhow::Result<()> {
                 String::from_utf8_lossy(&out.stderr).trim()
             ));
         }
+    }
     Ok(())
 }
 
@@ -190,12 +312,13 @@ pub(crate) fn provision(
         script.push_str(&format!("sif {guest} mode 0{:o}\n", 0o100000 | mode));
     }
     std::fs::write(&cmds, script).with_context(|| format!("writing {}", cmds.display()))?;
-    let out = Command::new("debugfs")
+    let out = debugfs_tool()
+        .ok_or_else(|| anyhow!("debugfs not found: install e2fsprogs"))?
         .args(["-w", "-f"])
         .arg(&cmds)
         .arg(image)
         .output()
-        .map_err(|e| anyhow!("debugfs not found ({e}): install e2fsprogs; the snap stages it"))?;
+        .map_err(|e| anyhow!("debugfs not runnable ({e})"))?;
     let _ = std::fs::remove_file(&cmds);
     if !out.status.success() {
         return Err(anyhow!(
@@ -212,12 +335,13 @@ pub(crate) fn provision(
 /// reader (the exit-code control file) holds an integer, so those
 /// lines are dropped. An absent file reads back empty.
 pub(crate) fn read_file(image: &Path, guest: &str) -> anyhow::Result<String> {
-    let out = Command::new("debugfs")
+    let out = debugfs_tool()
+        .ok_or_else(|| anyhow!("debugfs not found: install e2fsprogs"))?
         .arg("-R")
         .arg(format!("cat {guest}"))
         .arg(image)
         .output()
-        .map_err(|e| anyhow!("debugfs not found ({e}): install e2fsprogs"))?;
+        .map_err(|e| anyhow!("debugfs not runnable ({e})"))?;
     let text = String::from_utf8_lossy(&out.stdout);
     Ok(text
         .lines()
@@ -229,12 +353,13 @@ pub(crate) fn read_file(image: &Path, guest: &str) -> anyhow::Result<String> {
 /// Whether a guest path exists in the image: a debugfs stat that finds
 /// an inode. Symlinks resolve; stat follows them like the guest will.
 pub(crate) fn stat_exists(image: &Path, guest: &str) -> anyhow::Result<bool> {
-    let out = Command::new("debugfs")
+    let out = debugfs_tool()
+        .ok_or_else(|| anyhow!("debugfs not found: install e2fsprogs"))?
         .arg("-R")
         .arg(format!("stat {guest}"))
         .arg(image)
         .output()
-        .map_err(|e| anyhow!("debugfs not found ({e}): install e2fsprogs"))?;
+        .map_err(|e| anyhow!("debugfs not runnable ({e})"))?;
     Ok(String::from_utf8_lossy(&out.stdout).contains("Inode:"))
 }
 
@@ -256,8 +381,8 @@ mod tests {
     use std::os::unix::fs::MetadataExt;
 
     fn have_e2fsprogs() -> bool {
-        Command::new("mkfs.ext4").arg("-V").output().is_ok()
+        crate::utils::find_tool("mkfs.ext4").is_some()
-            && Command::new("debugfs").arg("-V").output().is_ok()
+            && crate::utils::find_tool("debugfs").is_some()
     }
 
     /// A tarball with one root-owned directory and a file owned by uid
@@ -343,13 +468,16 @@ mod tests {
         assert!(looks_like_ext4(&image), "the built image lacks the magic");
         assert!(!work.path().join("rootfs.part").exists());
 
-        let out = Command::new("debugfs")
+        let out = debugfs_tool()
+            .unwrap()
             .arg("-R")
             .arg("stat /etc/marker")
             .arg(&image)
             .output()
             .unwrap();
         let stat = String::from_utf8_lossy(&out.stdout);
+        if mke2fs_reads_tarballs() {
+            // Tarball populate bakes the archive's owners in.
             assert!(
                 stat.lines()
                     .any(|l| l.contains("User:") && l.contains("104")),
@@ -360,6 +488,17 @@ mod tests {
                     .any(|l| l.contains("Group:") && l.contains("104")),
                 "{stat}"
             );
+        } else {
+            // The tree fallback cannot: every entry carries the
+            // invoking user's ids, which is the documented loss.
+            use std::os::unix::fs::MetadataExt;
+            let uid = std::fs::metadata(&image).unwrap().uid();
+            assert!(
+                stat.lines()
+                    .any(|l| l.contains("User:") && l.contains(&uid.to_string())),
+                "{stat}"
+            );
+        }
     }
 
     #[test]
@@ -393,7 +532,8 @@ mod tests {
         assert!(stat_exists(&image, "/ecrou-init").unwrap());
         assert!(!stat_exists(&image, "/etc/marker-does-not-exist").unwrap());
 
-        let out = Command::new("debugfs")
+        let out = debugfs_tool()
+            .unwrap()
             .arg("-R")
             .arg("stat /ecrou-init")
             .arg(&image)

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
+//! The library (`libkrun.so.1` on Linux, `libkrun.1.dylib` on macOS)
-//! install is a remediation message rather than a link error. The
+//! 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
+//! our process and touches only files and sockets (plus `/dev/kvm` on
-//! inside the confinement budget (SPEC.md).
+//! 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
+/// Remediation shown when libkrun cannot be loaded: on macOS the
-/// still sparse (Fedora carries it; Debian and Ubuntu do not yet).
+/// 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`
+        let candidates = load_candidates();
-        // and every symbol below is used through it.
+        let mut last: Option<anyhow::Error> = None;
-        let lib = unsafe { libloading::Library::new(SONAME) }
+        for candidate in &candidates {
-            .with_context(|| format!("cannot load {SONAME}: {LOAD_REMEDIATION}"))?;
+            // Safety: dlopen of a fixed name; the handle lives in
-        Ok(Krun { lib })
+            // `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
+/// Probe the host hypervisor. On Linux that is KVM: open `/dev/kvm`
-/// `KVM_GET_API_VERSION` returns 12.
+/// read-write, then check `KVM_GET_API_VERSION` returns 12. On macOS
-pub fn kvm_probe() -> Result<()> {
+/// 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!(
+                // The remediation names the platform's install path:
-                    msg.contains("LD_LIBRARY_PATH"),
+                // the loader variable on Linux, the brew tap on macOS.
-                    "remediation missing: {msg}"
+                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
+//! ([`Error::KvmUnavailable`], [`Error::HvUnavailable`],
-//! ordinary failures ([`Error::Other`], which preserves the full context
+//! [`Error::ArchNotAvailable`]) versus ordinary failures
-//! chain).
+//! ([`Error::Other`], which preserves the full context chain).
 //!
 //! ## Crate split
 //!

crates/ecrou/src/rootfs.rs

@@ -405,10 +405,8 @@ mod tests {
     use crate::progress::NoProgress;
 
     fn have_e2fsprogs() -> bool {
-        std::process::Command::new("mkfs.ext4")
+        crate::utils::find_tool("mkfs.ext4").is_some()
-            .arg("-V")
+            && crate::utils::find_tool("debugfs").is_some()
-            .output()
-            .is_ok()
     }
 
     #[test]
@@ -447,9 +445,10 @@ mod tests {
             .unwrap();
         tar.into_inner().unwrap().finish().unwrap();
 
-        let req = PrepareRequest::new(
+        let mut req = PrepareRequest::new(
             "ubuntu@sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
         );
+        req.arch = "amd64".to_string();
         let pulled = cache.pull(&req, &NoProgress).unwrap();
         assert!(!pulled.downloaded);
         assert_eq!(pulled.cache_path, entry);
@@ -474,9 +473,10 @@ mod tests {
         // real pull flow.
         let dir = tempfile::tempdir().unwrap();
         let cache = RootfsCache::new(dir.path().to_path_buf());
-        let req = PrepareRequest::new(
+        let mut req = PrepareRequest::new(
             "ubuntu@sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb",
         );
+        req.arch = "amd64".to_string();
         // A pinned OCI source resolves without the network, so
         // parse_image_ref succeeds; the entry is absent, so pull takes
         // the download path and fails in fill_entry (no registry
@@ -502,7 +502,8 @@ mod tests {
         touch_entry(&cache, "alpine-3.23.0-x86_64.tar.gz");
         touch_entry(&cache, "alpine-3.22.9-x86_64.tar.gz");
 
-        let req = PrepareRequest::new("alpine:3.23");
+        let mut req = PrepareRequest::new("alpine:3.23");
+        req.arch = "amd64".to_string();
         let (source, path, downloaded) = cache.ensure_entry(&req, &NoProgress, false).unwrap();
         assert!(!downloaded);
         assert_eq!(path, dir.path().join("alpine-3.23.0-x86_64.tar.gz"));
@@ -519,7 +520,8 @@ mod tests {
         touch_entry(&cache, "alpine-3.20.3-x86_64.tar.gz");
         touch_entry(&cache, "alpine-3.23.0-x86_64.tar.gz");
 
-        let req = PrepareRequest::new("alpine:3.23");
+        let mut req = PrepareRequest::new("alpine:3.23");
+        req.arch = "amd64".to_string();
         let (_, path, _) = cache.ensure_entry(&req, &NoProgress, false).unwrap();
         assert_eq!(path, dir.path().join("alpine-3.23.0-x86_64.tar.gz"));
     }
@@ -531,13 +533,15 @@ mod tests {
         touch_entry(&cache, "alpine-20250401-x86_64.tar.gz");
         touch_entry(&cache, "alpine-3.23.0-x86_64.tar.gz");
 
-        let req = PrepareRequest::new("alpine:edge");
+        let mut req = PrepareRequest::new("alpine:edge");
+        req.arch = "amd64".to_string();
         let (_, path, _) = cache.ensure_entry(&req, &NoProgress, false).unwrap();
         assert_eq!(path, dir.path().join("alpine-20250401-x86_64.tar.gz"));
 
         // Plain "alpine" floats among releases; the edge date is
         // invisible to it.
-        let req = PrepareRequest::new("alpine");
+        let mut req = PrepareRequest::new("alpine");
+        req.arch = "amd64".to_string();
         let (_, path, _) = cache.ensure_entry(&req, &NoProgress, false).unwrap();
         assert_eq!(path, dir.path().join("alpine-3.23.0-x86_64.tar.gz"));
     }
@@ -549,7 +553,8 @@ mod tests {
         touch_entry(&cache, "ubuntu-24.04-amd64.tar.gz");
         touch_entry(&cache, "ubuntu-26.04-amd64.tar.gz");
 
-        let req = PrepareRequest::new("ubuntu:lts");
+        let mut req = PrepareRequest::new("ubuntu:lts");
+        req.arch = "amd64".to_string();
         let (source, _, _) = cache.ensure_entry(&req, &NoProgress, false).unwrap();
         let ImageSource::DirectTarball { version, .. } = source else {
             panic!("expected a direct tarball");
@@ -599,7 +604,8 @@ mod tests {
         // tree itself: the marker is read back out of the image.
         let image = rootfs.dir().join("rootfs.img");
         assert!(image.exists());
-        let out = std::process::Command::new("debugfs")
+        let debugfs = crate::utils::find_tool("debugfs").unwrap();
+        let out = std::process::Command::new(debugfs)
             .arg("-R")
             .arg("cat /etc-marker")
             .arg(&image)

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
@@ -37,8 +85,16 @@ 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);
+        }
+        #[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
@@ -46,6 +102,7 @@ pub(crate) fn spawn_machine(
         // 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 +160,96 @@ 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 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)?;

packaging/homebrew/Formula/ecrou.rb

@@ -0,0 +1,42 @@
+# The formula lives in the repo and ships through the
+# vhaudiquet/homebrew-ecrou tap; it needs the same tap libkrun's
+# krunkit comes from, because the engine is dlopen'd from those kegs
+# at runtime.
+class Ecrou < Formula
+  desc "a small microVM runtime based on libkrun"
+  homepage "https://github.com/vhaudiquet/ecrou"
+  # Placeholder pin: the release workflow rewrites url and sha256 on publish.
+  url "https://github.com/vhaudiquet/ecrou.git", tag: "v0.1.0"
+  license "MIT"
+
+  # libkrun's Hypervisor.framework backend is arm64-only upstream.
+  depends_on arch: :arm64
+  depends_on "libkrun/homebrew-krun/libkrun"
+  depends_on "e2fsprogs"
+  # A libarchive-capable mke2fs populates ext4 images from tarballs in
+  # one pass; without it the build falls back to a per-file tree walk.
+  depends_on "libarchive"
+
+  def install
+    # CI signed the binary with the hypervisor entitlement (a hard
+    # requirement on current macOS, the same one krunkit's formula
+    # signs for); a rebuild here would strip the signature, so the
+    # release tarball's binary is poured as-is.
+    bin.install "ecrou"
+  end
+
+  def caveats
+    <<~EOS
+      The binary is ad-hoc signed with the com.apple.security.hypervisor
+      entitlement. Rebuilding from source (cargo) requires re-signing:
+        codesign --force --sign - --entitlements packaging/homebrew/ecrou.entitlements target/release/ecrou
+      `ecrou probe` reports this when the entitlement is missing.
+    EOS
+  end
+
+  test do
+    system bin/"ecrou", "probe"
+    output = shell_output("#{bin}/ecrou run --quiet alpine -- uname -r").strip
+    assert_match(/\d+\.\d+/, output)
+  end
+end

packaging/homebrew/ecrou.entitlements

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0"><dict>
+<key>com.apple.security.hypervisor</key><true/>
+</dict></plist>