Rework the backend project structure.

This cleans up some old cruft.

.github/workflows/ci.yml

@@ -19,18 +19,22 @@ jobs:
           - name: Linux x86_64
             os: ubuntu-24.04
             target: x86_64-unknown-linux-gnu
+            arguments: ""
 
           - name: Linux x86
             os: ubuntu-24.04
             target: i686-unknown-linux-gnu
+            arguments: ""
 
           - name: Linux riscv64gc
             os: ubuntu-24.04
             target: riscv64gc-unknown-linux-gnu
+            arguments: "--features=experimental_riscv"
 
           - name: MacOS aarch64
             os: macos-latest
             target: aarch64-apple-darwin
+            arguments: ""
 
     name: Clippy ${{ matrix.name }}
     runs-on: ${{ matrix.os }}
@@ -59,7 +63,7 @@ jobs:
           cargo clippy --target ${{ matrix.target }} --no-default-features
 
           # Check with default features
-          cargo clippy --target ${{ matrix.target }}
+          cargo clippy --target ${{ matrix.target }} ${{ matrix.arguments }}
 
   test:
     timeout-minutes: 30
@@ -98,37 +102,31 @@ jobs:
         shell: bash
         run: |
           set -e
-          cargo test
+          cargo test --lib
 
-      - name: Tests (force_fallback)
+      - name: Tests (force_software)
         shell: bash
         run: |
           set -e
-          cargo test --features=force_fallback
+          cargo test --lib --features=force_software
 
-      - name: Tests (force_no_runtime_detection)
+      - name: Tests (force_runtime_detection)
         shell: bash
         run: |
           set -e
-          cargo test --features=force_fallback,force_no_runtime_detection
+          cargo test --lib --features=force_runtime_detection
 
       - name: Tests no-std
         shell: bash
         run: |
           set -e
-          cargo test --no-default-features
+          cargo test --lib --no-default-features
 
-      - name: Tests no-std (force_fallback)
+      - name: Tests no-std (force_software)
         shell: bash
         run: |
           set -e
-          cargo test --no-default-features --features=force_fallback
-
-      - name: Tests no-std (force_no_runtime_detection)
-        shell: bash
-        run: |
-          set -e
-          cargo test --no-default-features --features=force_fallback,force_no_runtime_detection
+          cargo test --lib --no-default-features --features=force_software
 
   verification:
     timeout-minutes: 30

Cargo.toml

@@ -22,10 +22,10 @@ tls = ["std"]
 experimental_riscv = []
 
 ### The following features are only used internally and are unstable ###
-# Forces the compiler to always use the fallback (never using the hardware AES directly).
-force_fallback = []
-# Deactivates the runtime target feature detection. Combined with `force_fallback` this forced to always using the software AES.
-force_no_runtime_detection = []
+# Forces the compiler to enable the runtime detection.
+force_runtime_detection = []
+# Forces the compiler to enable the software backend.
+force_software = []
 # Enables some functionality used for the verification executable used in CI.
 verification = ["std"]
 

src/hardware/aarch64.rs → src/backend/aarch64.rs

@@ -430,19 +430,17 @@ pub unsafe fn aes_key_expansion<const L: usize, const N: usize>(key: [u8; L]) ->
 
 #[cfg(all(
     test,
-    not(any(
-        not(all(
-            target_arch = "aarch64",
-            target_feature = "neon",
-            target_feature = "aes",
-        )),
-        feature = "force_fallback"
-    ))
+    all(
+        target_arch = "aarch64",
+        target_feature = "neon",
+        target_feature = "aes",
+    ),
+    not(feature = "verification")
 ))]
 mod tests {
     use super::*;
     use crate::constants::{AES128_KEY_COUNT, AES128_KEY_SIZE, AES_BLOCK_SIZE};
-    use crate::hardware::tests::{aes128_key_expansion_test, aes256_key_expansion_test};
+    use crate::tests::{aes128_key_expansion_test, aes256_key_expansion_test};
 
     #[test]
     fn test_aes128_key_expansion() {

src/backend/mod.rs

@@ -0,0 +1,35 @@
+#[cfg(all(target_arch = "aarch64", not(feature = "force_software")))]
+pub(crate) mod aarch64;
+
+#[cfg(all(
+    target_arch = "riscv64",
+    feature = "experimental_riscv",
+    not(feature = "force_software")
+))]
+pub(crate) mod riscv64;
+
+#[cfg(all(
+    any(target_arch = "x86_64", target_arch = "x86"),
+    not(feature = "force_software")
+))]
+pub(crate) mod x86;
+
+#[cfg(any(
+    not(any(
+        all(
+            any(target_arch = "x86_64", target_arch = "x86"),
+            target_feature = "sse2",
+            target_feature = "aes",
+        ),
+        all(target_arch = "riscv64", feature = "experimental_riscv"),
+        all(
+            target_arch = "aarch64",
+            target_feature = "neon",
+            target_feature = "aes",
+        ),
+    )),
+    feature = "force_runtime_detection",
+    feature = "force_software",
+    feature = "verification",
+))]
+pub(crate) mod soft;

src/hardware/riscv64.rs → src/backend/riscv64.rs

@@ -1,9 +1,6 @@
-use core::{
-    arch::asm,
-    cell::{Cell, RefCell},
-};
+use core::{arch::asm, cell::Cell};
 
-use crate::constants::{AES128_KEY_COUNT, AES128_KEY_SIZE, AES256_KEY_COUNT, AES256_KEY_SIZE};
+use crate::constants::{AES128_KEY_COUNT, AES256_KEY_COUNT};
 
 /// A random number generator based on the AES-128 block cipher that runs in CTR mode and has a
 /// period of 64-bit.
@@ -69,6 +66,7 @@ impl Aes128Ctr64 {
     }
 
     #[inline(always)]
+    #[allow(unused_assignments)]
     pub(crate) unsafe fn next_impl(&self) -> u128 {
         // Increment the lower 64 bits.
         let counter = self.counter.get();
@@ -80,7 +78,7 @@ impl Aes128Ctr64 {
 
         // Initialize the state with the counter.
         let mut state = counter;
-        let state_ptr = (&mut state).as_mut_ptr();
+        let state_ptr = state.as_mut_ptr();
 
         asm!(
             "vsetivli x0, 4, e32, m1, ta, ma",
@@ -208,6 +206,7 @@ impl Aes128Ctr128 {
     }
 
     #[inline(always)]
+    #[allow(unused_assignments)]
     pub(crate) unsafe fn next_impl(&self) -> u128 {
         // Increment the counter.
         let counter = self.counter.get();
@@ -339,6 +338,7 @@ impl Aes256Ctr64 {
     }
 
     #[inline(always)]
+    #[allow(unused_assignments)]
     pub(crate) unsafe fn next_impl(&self) -> u128 {
         // Increment the lower 64 bits.
         let counter = self.counter.get();
@@ -350,7 +350,7 @@ impl Aes256Ctr64 {
 
         // Initialize the state with the counter.
         let mut state = counter;
-        let state_ptr = (&mut state).as_mut_ptr();
+        let state_ptr = state.as_mut_ptr();
 
         asm!(
             "vsetivli x0, 4, e32, m1, ta, ma",
@@ -500,6 +500,7 @@ impl Aes256Ctr128 {
     }
 
     #[inline(always)]
+    #[allow(unused_assignments)]
     pub(crate) unsafe fn next_impl(&self) -> u128 {
         // Increment the counter.
         let counter = self.counter.get();
@@ -585,10 +586,11 @@ impl Aes256Ctr128 {
     }
 }
 
+#[allow(unused_assignments)]
 unsafe fn aes128_key_expansion(key: u128) -> [u128; AES128_KEY_COUNT] {
     let mut expanded_keys = [0u128; AES128_KEY_COUNT];
     let key_ptr = &key as *const u128;
-    let mut expanded_ptr = (&mut expanded_keys).as_mut_ptr();
+    let mut expanded_ptr = expanded_keys.as_mut_ptr();
 
     asm!(
         "vsetivli x0, 4, e32, m4, ta, ma",
@@ -633,10 +635,11 @@ unsafe fn aes128_key_expansion(key: u128) -> [u128; AES128_KEY_COUNT] {
     expanded_keys
 }
 
+#[allow(unused_assignments)]
 unsafe fn aes256_key_expansion(key: [u128; 2]) -> [u128; AES256_KEY_COUNT] {
     let mut expanded_keys = [0u128; AES256_KEY_COUNT];
     let mut key_ptr = &key as *const u128;
-    let mut expanded_ptr = (&mut expanded_keys).as_mut_ptr();
+    let mut expanded_ptr = expanded_keys.as_mut_ptr();
 
     asm!(
         "vsetivli x0, 4, e32, m4, ta, ma",
@@ -695,11 +698,16 @@ unsafe fn aes256_key_expansion(key: [u128; 2]) -> [u128; AES256_KEY_COUNT] {
     expanded_keys
 }
 
-#[cfg(all(test, not(feature = "force_fallback")))]
+#[cfg(all(
+    test,
+    target_arch = "riscv64",
+    feature = "experimental_riscv",
+    not(feature = "verification")
+))]
 mod tests {
     use super::*;
     use crate::constants::{AES128_KEY_COUNT, AES128_KEY_SIZE, AES_BLOCK_SIZE};
-    use crate::hardware::tests::{aes128_key_expansion_test, aes256_key_expansion_test};
+    use crate::tests::{aes128_key_expansion_test, aes256_key_expansion_test};
 
     #[test]
     fn test_aes128_key_expansion() {