deb/cross: stop exporting PKG_CONFIG_LIBDIR for cross builds

dpkg-buildpackage and sbuild export no pkg-config redirection: the
environment is the package's to set.  Pointing the whole build at the
target multiarch pkgconfig dirs makes every pkg-config-consuming tool
resolve against the target libraries, the host-side tools of the same
build included: the host linker is then handed target-arch -L paths
(the kernel's resolve_btfids logging 'skipping incompatible
/usr/lib/aarch64-linux-gnu/libelf.so') and only survives through
fallbacks when the build-architecture libraries happen to be installed
too.

Packages whose cross builds need target pkg-config data must arrange
for it themselves, the way the kernel packaging builds rtla statically
against no target system libraries.

README.md

@@ -6,7 +6,13 @@
 
 ## Installation
 
-No distribution channel is published yet; build from source:
+From crates.io:
+
+```
+cargo install pkh
+```
+
+Or build from source (the same system packages are needed either way):
 
 ```
 sudo apt install pkg-config libssl-dev libgpg-error-dev libgpgme-dev

data/quirks.yml

@@ -15,18 +15,38 @@ quirks:
   # against the host architecture, whose dependency closure conflicts with
   # the `:native` python3. Resolve it against the build architecture
   # until the control is fixed upstream.
+  # The resolute and stonking kernels declare the host-tool libraries
+  # unqualified (libelf-dev for resolve_btfids, libdw-dev for
+  # gendwarfksyms, libssl-dev for sign-file), unlike the Debian control,
+  # which carries the same names qualified `:native`.  The dpkg cross
+  # rules resolve an unqualified Multi-Arch: same name against the host
+  # architecture only, so a cross build installs no build-architecture
+  # variants and the kernel's host-side tools cannot link.  Inject the
+  # build-architecture variants until the control is fixed upstream.
   linux:
     deb:
       - series: [resolute]
         dependencies:
           replace:
             llvm-21-dev: llvm-21-dev:native <!stage1>
+      - series: [resolute, stonking]
+        dependencies:
+          inject:
+            - libelf-dev:native
+            - libdw-dev:native
+            - libssl-dev:native
   linux-riscv:
     deb:
       - series: [resolute]
         dependencies:
           replace:
             llvm-21-dev: llvm-21-dev:native <!stage1>
+      - series: [resolute, stonking]
+        dependencies:
+          inject:
+            - libelf-dev:native
+            - libdw-dev:native
+            - libssl-dev:native
 
   # Add more packages and their quirks as needed
   # example-package:

src/deb/cross.rs

@@ -62,20 +62,6 @@ pub fn setup_environment(
         .map_err(|e| format!("Invalid UTF-8 in dpkg-architecture output: {e}"))?;
     parse_dpkg_architecture_output(&dpkg_architecture, env);
 
-    // In-tree tools locate their libraries with the *host* pkg-config during
-    // cross builds (the kernel's tools/build feature checks derive their
-    // cflags/ldflags from `pkg-config --cflags/--libs`), whose search path
-    // only covers the build architecture's pkgconfig dirs. Point it at the
-    // target's so `libtraceevent` & co resolve to target-arch libraries:
-    // linux-riscv cross builds die in rtla's Makefile.config otherwise, even
-    // with the target -dev packages installed.
-    if let Some(multiarch) = env.get("DEB_HOST_MULTIARCH").cloned() {
-        env.insert(
-            "PKG_CONFIG_LIBDIR".to_string(),
-            format!("/usr/lib/{multiarch}/pkgconfig:/usr/share/pkgconfig"),
-        );
-    }
-
     env.insert("DEB_BUILD_PROFILES".to_string(), "cross".to_string());
 
     Ok(())
@@ -304,21 +290,18 @@ mod tests {
         assert!(cross_suites("noble", None, "not-a-distro").is_err());
     }
 
-    /// setup_environment exports the target multiarch pkg-config libdir:
-    /// tools' feature checks run the *host* pkg-config, which must find the
-    /// target's .pc files (rtla hard-errors on libtraceevent otherwise,
-    /// failing linux-riscv cross builds despite the target -dev packages
-    /// being installed).
+    /// setup_environment exports the dpkg cross variables and the 'cross'
+    /// build profile, and nothing beyond what dpkg-buildpackage exports:
+    /// no pkg-config redirection (the environment is the package's to
+    /// set, and target-arch pkgconfig paths would also poison the
+    /// host-side tools of the same build).
     #[test]
-    fn test_setup_environment_exports_cross_pkg_config_libdir() {
+    fn test_setup_environment_exports_dpkg_cross_variables_only() {
         let mut env = HashMap::new();
         let ctx = Arc::new(Context::new(crate::context::ContextConfig::Local).unwrap());
         setup_environment(&mut env, "riscv64", ctx).unwrap();
 
-        assert_eq!(
-            env.get("PKG_CONFIG_LIBDIR").map(String::as_str),
-            Some("/usr/lib/riscv64-linux-gnu/pkgconfig:/usr/share/pkgconfig")
-        );
+        assert!(!env.contains_key("PKG_CONFIG_LIBDIR"));
         assert_eq!(
             env.get("DEB_BUILD_PROFILES").map(String::as_str),
             Some("cross")

src/deb/local.rs

@@ -1154,6 +1154,39 @@ mod tests {
         assert_eq!(spec, "t:amd64");
     }
 
+    /// Cross parity with dpkg's checker and sbuild's apt-resolved dummy
+    /// package: an unqualified Multi-Arch: same name resolves to the
+    /// host-architecture variant even when a build-architecture candidate
+    /// exists — the build-architecture side is only ever installed
+    /// through an explicit `:native` declaration (or a pkh quirk
+    /// injecting one), never alongside the host variant.
+    #[test]
+    fn install_spec_unqualified_same_package_never_dual_installs() {
+        let host = "arm64";
+        let build = "amd64";
+
+        let spec = install_spec_for(
+            &rel("t"),
+            &[cand("amd64", "same"), cand("arm64", "same")],
+            build,
+            host,
+        )
+        .unwrap();
+        assert_eq!(spec, "t:arm64");
+
+        // The build-architecture side comes from `:native` declarations:
+        // the co-installable build-arch variant of the same source
+        // package.
+        let spec = install_spec_for(
+            &rel("t:native"),
+            &[cand("amd64", "same"), cand("arm64", "same")],
+            build,
+            host,
+        )
+        .unwrap();
+        assert_eq!(spec, "t:amd64");
+    }
+
     /// Qualified dependencies install exactly the variant their qualifier
     /// selects per dpkg semantics; virtual names (no candidates) pass
     /// through unqualified for apt to resolve a provider.

src/quirks.rs

@@ -265,15 +265,62 @@ mod tests {
     fn linux_dependency_quirks_are_series_scoped() {
         for package in ["linux", "linux-riscv"] {
             let rules = get_deb_dependency_quirks(package, "resolute");
-            assert_eq!(rules.len(), 1, "the resolute entry applies");
+            assert_eq!(rules.len(), 2, "the resolute entries apply");
             assert_eq!(
                 rules[0].replace.get("llvm-21-dev").map(String::as_str),
                 Some("llvm-21-dev:native <!stage1>")
             );
+            // Only the stonking entry exists there: the llvm-21-dev
+            // replacement above is a resolute-only packaging state.
+            let rules = get_deb_dependency_quirks(package, "stonking");
+            assert_eq!(rules.len(), 1);
+            assert!(rules[0].replace.is_empty());
             assert!(get_deb_dependency_quirks(package, "noble").is_empty());
         }
     }
 
+    /// The kernels of the series whose control dropped the Debian-style
+    /// `:native` qualifiers on the host-tool libraries inject the
+    /// build-architecture variants: the dpkg cross rules resolve the
+    /// unqualified Multi-Arch: same names against the host architecture
+    /// only, leaving nothing for the kernel's host-side tools to link.
+    #[test]
+    fn linux_injects_native_host_tool_libraries_for_cross() {
+        for series in ["resolute", "stonking"] {
+            let mut clauses = vec![vec![parse("libelf-dev <!stage1>")]];
+            crate::quirks::apply_dependency_quirks("linux", series, &mut clauses, &opts()).unwrap();
+            let injected: Vec<&PkgRelation> = clauses[1..]
+                .iter()
+                .flatten()
+                .filter(|rel| {
+                    ["libelf-dev", "libdw-dev", "libssl-dev"].contains(&rel.package.as_str())
+                })
+                .collect();
+            assert_eq!(
+                injected.len(),
+                3,
+                "one :native clause per host-tool library"
+            );
+            assert!(
+                injected
+                    .iter()
+                    .all(|rel| rel.arch_qualifier.as_deref() == Some("native"))
+            );
+            // The declared dependency itself is untouched: the host
+            // (target) variant still installs for the checker.
+            assert_eq!(clauses[0][0].arch_qualifier, None);
+        }
+    }
+
+    /// Other kernel series keep their declared dependencies untouched.
+    #[test]
+    fn noble_linux_dependencies_are_not_rewritten() {
+        let mut clauses = vec![vec![parse("libelf-dev")]];
+        crate::quirks::apply_dependency_quirks("linux", "noble", &mut clauses, &opts()).unwrap();
+        assert_eq!(clauses.len(), 1);
+        assert_eq!(clauses[0][0].arch_qualifier, None);
+    }
+
     /// `replace` rewrites exactly the dependencies whose declared name
     /// matches, wholesale: the replacement carries its own qualifier and
     /// restrictions.