fix libfdt static linking

Signed-off-by: Serban Iorga <[email protected]>

Author: Serban Iorga

.cargo/config

@@ -2,14 +2,5 @@
 target = "x86_64-unknown-linux-musl"
 target-dir = "build/cargo_target"
 
-[target.'cfg(any(target_arch="arm", target_arch="aarch64"))']
-# On aarch64 musl depends on some libgcc functions (i.e `__addtf3` and other `*tf3` functions) for logic that uses
-# long double. Such functions are not builtin in the rust compiler, so we need to get them from libgcc.
-# No need for the `crt_static` flag as rustc appends it by default.
-rustflags = [
-	"-C", "link-arg=-lgcc",
-	"-C", "link-arg=-lfdt",
-]
-
 [net]
 git-fetch-with-cli = true

src/libfdt-bindings/Cargo.toml

@@ -3,6 +3,7 @@ name = "libfdt-bindings"
 version = "0.1.0"
 authors = ["Amazon Firecracker team <[email protected]>"]
 edition = "2018"
+build = "build.rs"
 
 [target.'cfg(target_arch="aarch64")'.dependencies]
 libc = ">=0.2.39"

src/libfdt-bindings/build.rs

@@ -0,0 +1,47 @@
+// Copyright 2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+use std::process::Command;
+
+/// Get the ld linker search paths
+///
+/// Cargo overwrites LD_LIBRARY_PATH with rust specific paths. But we need the default system
+/// paths in order to find libfdt. So we query `ld` in order to get them.
+fn get_ld_search_dirs() -> Vec<String> {
+    // We need to extract from `ld --verbose` all the search paths.
+    // For example `ld --verbose | grep SEARCH_DIR | tr -s ' ;' '\n'` returns the following:
+    // ```
+    // SEARCH_DIR("=/usr/local/lib/aarch64-linux-gnu")
+    // SEARCH_DIR("=/lib/aarch64-linux-gnu")
+    // SEARCH_DIR("=/usr/lib/aarch64-linux-gnu")
+    // SEARCH_DIR("=/usr/local/lib")
+    // SEARCH_DIR("=/lib")
+    // SEARCH_DIR("=/usr/lib")
+    // SEARCH_DIR("=/usr/aarch64-linux-gnu/lib")
+    // ```
+    let cmd = r#"
+        ld --verbose | grep -oP '(?<=SEARCH_DIR\(\"=)[^"]+(?=\"\);)'
+    "#;
+
+    Command::new("sh")
+        .arg("-c")
+        .arg(cmd)
+        .output()
+        .ok()
+        .and_then(|output| {
+            if output.status.success() {
+                return Some(output.stdout);
+            }
+            None
+        })
+        .and_then(|stdout_bytes| String::from_utf8(stdout_bytes).ok())
+        .map_or(vec![], |stdout| {
+            stdout.lines().map(|item| item.to_string()).collect()
+        })
+}
+
+fn main() {
+    for ld_search_dir in get_ld_search_dirs() {
+        println!("cargo:rustc-link-search=native={}", ld_search_dir);
+    }
+}

src/libfdt-bindings/src/lib.rs

@@ -8,6 +8,7 @@ use libc::{c_char, c_int, c_void};
 // flattened device tree (fdt) that is passed to the kernel and indicates
 // the hardware configuration of the machine.
 #[cfg(target_arch = "aarch64")]
+#[link(name = "fdt", kind = "static")]
 extern "C" {
     pub fn fdt_create(buf: *mut c_void, bufsize: c_int) -> c_int;
     pub fn fdt_finish_reservemap(fdt: *mut c_void) -> c_int;