Add linkage attributes to extern "C" blocks

build.rs

@@ -230,6 +230,7 @@ fn build_avx512_assembly() {
 }
 
 fn build_neon_c_intrinsics() {
+    println!("cargo:rustc-cfg=blake3_neon_ffi");
     let mut build = new_build();
     // Note that blake3_neon.c normally depends on the blake3_portable.c
     // for the single-instance compression function, but we expose
@@ -254,7 +255,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         "blake3_avx2_ffi",
         "blake3_avx2_rust",
         "blake3_avx512_ffi",
-        "blake3_neon",
+        "blake3_neon_ffi",
     ];
     for cfg_name in all_cfgs {
         // TODO: Switch this whole file to the new :: syntax when our MSRV reaches 1.77.
@@ -296,7 +297,6 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     if (is_arm() && is_neon())
         || (!is_no_neon() && !is_pure() && is_aarch64() && is_little_endian())
     {
-        println!("cargo:rustc-cfg=blake3_neon");
         build_neon_c_intrinsics();
     }
 

src/ffi_avx2.rs

@@ -33,6 +33,10 @@ pub unsafe fn hash_many<const N: usize>(
 }
 
 pub mod ffi {
+    #[cfg_attr(
+        blake3_avx2_ffi,
+        link(name = "blake3_sse2_sse41_avx2_assembly", kind = "static")
+    )]
     extern "C" {
         pub fn blake3_hash_many_avx2(
             inputs: *const *const u8,

src/ffi_avx512.rs

@@ -61,6 +61,10 @@ pub unsafe fn hash_many<const N: usize>(
 }
 
 pub mod ffi {
+    #[cfg_attr(
+        blake3_avx512_ffi,
+        link(name = "blake3_avx512_assembly", kind = "static")
+    )]
     extern "C" {
         pub fn blake3_compress_in_place_avx512(
             cv: *mut u32,

src/ffi_neon.rs

@@ -53,6 +53,7 @@ pub extern "C" fn blake3_compress_in_place_portable(
 }
 
 pub mod ffi {
+    #[cfg_attr(blake3_neon_ffi, link(name = "blake3_neon", kind = "static"))]
     extern "C" {
         pub fn blake3_hash_many_neon(
             inputs: *const *const u8,

src/ffi_sse2.rs

@@ -61,6 +61,10 @@ pub unsafe fn hash_many<const N: usize>(
 }
 
 pub mod ffi {
+    #[cfg_attr(
+        blake3_sse2_ffi,
+        link(name = "blake3_sse2_sse41_avx2_assembly", kind = "static")
+    )]
     extern "C" {
         pub fn blake3_compress_in_place_sse2(
             cv: *mut u32,

src/ffi_sse41.rs

@@ -61,6 +61,10 @@ pub unsafe fn hash_many<const N: usize>(
 }
 
 pub mod ffi {
+    #[cfg_attr(
+        blake3_sse41_ffi,
+        link(name = "blake3_sse2_sse41_avx2_assembly", kind = "static")
+    )]
     extern "C" {
         pub fn blake3_compress_in_place_sse41(
             cv: *mut u32,