fix(linux): make the Linux build work on arm64

crates/compositor/src/audio.rs

@@ -35,7 +35,9 @@ extern "C" {
 
 fn averr(ret: i32, ctx: &str) -> Result<()> {
     if ret < 0 {
-        let mut buf = [0i8; 256];
+        // NOT `[0i8; 256]`: `c_char` is signed on x86_64 but UNSIGNED on aarch64, so a
+        // hardcoded i8 makes av_strerror's `*mut c_char` a type error on arm64.
+        let mut buf = [0 as ::std::os::raw::c_char; 256];
         unsafe { av_strerror(ret, buf.as_mut_ptr(), buf.len()) };
         let msg = unsafe { std::ffi::CStr::from_ptr(buf.as_ptr()) }.to_string_lossy();
         bail!("{ctx}: {ret} ({msg})");

electron/native/pipewire-capture/src/ffmpeg.rs

@@ -49,7 +49,9 @@ pub const AVIO_FLAG_WRITE: i32 = 2;
 /// Formats an ffmpeg return code the way `av_err2str` would, since that too is a
 /// macro and needs a caller-supplied buffer.
 pub fn err_to_string(code: i32) -> String {
-    let mut buffer = [0i8; 256];
+    // NOT `[0i8; 256]`: `c_char` is signed on x86_64 but UNSIGNED on aarch64, so a
+    // hardcoded i8 makes av_strerror's `*mut c_char` a type error on arm64.
+    let mut buffer = [0 as ::std::os::raw::c_char; 256];
     // SAFETY: the buffer is the size we tell av_strerror it is, and ffmpeg
     // always NUL-terminates within it.
     let ok = unsafe { av_strerror(code, buffer.as_mut_ptr(), buffer.len()) } == 0;

scripts/build-linux-compositor-addon.mjs

@@ -79,6 +79,13 @@ function resolveFfmpegDir() {
 	);
 }
 
+/**
+ * Debian/Ubuntu multiarch triplet for the host. Hardcoding the x86_64 one made
+ * both libclang and gcc's stddef.h invisible on arm64, where the same libraries
+ * live under /usr/lib/aarch64-linux-gnu.
+ */
+const MULTIARCH = process.arch === "arm64" ? "aarch64-linux-gnu" : "x86_64-linux-gnu";
+
 /**
  * bindgen loads libclang at runtime. crates/.cargo/config.toml hardcodes a
  * Windows LLVM path, so on Linux we locate it ourselves rather than making
@@ -88,7 +95,7 @@ function resolveLibclangDir() {
 	if (process.env.LIBCLANG_PATH) {
 		return process.env.LIBCLANG_PATH;
 	}
-	const roots = ["/usr/lib/x86_64-linux-gnu", "/usr/lib64", "/usr/lib"];
+	const roots = [`/usr/lib/${MULTIARCH}`, "/usr/lib64", "/usr/lib"];
 	for (const llvmRoot of ["/usr/lib"]) {
 		if (!fs.existsSync(llvmRoot)) continue;
 		for (const entry of fs.readdirSync(llvmRoot)) {
@@ -120,7 +127,7 @@ function bindgenClangArgs() {
 	if (process.env.BINDGEN_EXTRA_CLANG_ARGS) {
 		return process.env.BINDGEN_EXTRA_CLANG_ARGS;
 	}
-	const gccIncludeRoot = "/usr/lib/gcc/x86_64-linux-gnu";
+	const gccIncludeRoot = `/usr/lib/gcc/${MULTIARCH}`;
 	if (!fs.existsSync(gccIncludeRoot)) {
 		return "";
 	}

scripts/build-linux-pipewire-helper.mjs

@@ -63,9 +63,33 @@ if (cargoVersion.status !== 0) {
 	process.exit(1);
 }
 
+/**
+ * build.rs runs bindgen over the ffmpeg headers, and bindgen needs clang's own
+ * builtin includes (limits.h, stddef.h). Ubuntu ships libclang.so.1 without the
+ * matching resource dir, so clang finds neither and the build dies with
+ * "'limits.h' file not found". Point it at gcc's copies instead — the same
+ * fallback scripts/build-linux-compositor-addon.mjs already applies.
+ */
+function bindgenClangArgs() {
+	if (process.env.BINDGEN_EXTRA_CLANG_ARGS) {
+		return process.env.BINDGEN_EXTRA_CLANG_ARGS;
+	}
+	const multiarch = process.arch === "arm64" ? "aarch64-linux-gnu" : "x86_64-linux-gnu";
+	const gccIncludeRoot = `/usr/lib/gcc/${multiarch}`;
+	if (!fs.existsSync(gccIncludeRoot)) {
+		return "";
+	}
+	const withStddef = fs
+		.readdirSync(gccIncludeRoot)
+		.map((version) => path.join(gccIncludeRoot, version, "include"))
+		.filter((dir) => fs.existsSync(path.join(dir, "stddef.h")));
+	return withStddef.length > 0 ? `-I${withStddef[0]}` : "";
+}
+
 const build = spawnSync("cargo", ["build", "--release", "--manifest-path", manifest], {
 	cwd: crateDir,
 	stdio: "inherit",
+	env: { ...process.env, BINDGEN_EXTRA_CLANG_ARGS: bindgenClangArgs() },
 });
 if (build.error) {
 	console.error(`Failed to start cargo: ${build.error.message}`);

scripts/fetch-ffmpeg.mjs

@@ -111,6 +111,10 @@ const SHARED_PINNED = {
 		asset: "ffmpeg-n8.1.2-32-gcfa62de001-linux64-lgpl-shared-8.1.tar.xz",
 		sha256: "74ef679aa7e4f8cdbd5193da3d99bf220a679f64d35daf078397081b789f150e",
 	},
+	"linux-arm64": {
+		asset: "ffmpeg-n8.1.2-32-gcfa62de001-linuxarm64-lgpl-shared-8.1.tar.xz",
+		sha256: "d1d632deac102b865d43ef3c1eca0d0f8c0df148b784327d1d381a39159f8285",
+	},
 	"win32-x64": {
 		asset: "ffmpeg-n8.1.2-32-gcfa62de001-win64-lgpl-shared-8.1.zip",
 		sha256: "23429f940316ea92e376f6946c0a1f1b9043c930f3bc068228461d65ae24f8b8",