aes: consolidate backend configuration under aes_backend (#541)

Consolidates the previous `cfg` options `aes_force_soft`, `aes_avx256`,
and `aes_avx512` as `aes_backend` values:

- `avx256`
- `avx512`
- `soft`

The `aes_compact` option has been retained as-is so it can be used in
conjunction with the other options, though perhaps we can find some
other solution for it.

This does have the effect of preventing `avx256` and `avx512` from being
simultaneously enabled, although I'm not sure that would ever actually
make sense?

Author: tarcieri

.github/workflows/aes.yml

@@ -49,17 +49,17 @@ jobs:
           cargo build --target ${{ matrix.target }}
           cargo build --target ${{ matrix.target }} --features hazmat
       - env:
-          RUSTFLAGS: "-Dwarnings --cfg aes_force_soft"
+          RUSTFLAGS: '-Dwarnings --cfg aes_backend="soft"'
         run: |
           cargo build --target ${{ matrix.target }}
           cargo build --target ${{ matrix.target }} --features hazmat
       - env:
-          RUSTFLAGS: "-Dwarnings --cfg aes_compact"
+          RUSTFLAGS: '-Dwarnings --cfg aes_compact'
         run: |
           cargo build --target ${{ matrix.target }}
           cargo build --target ${{ matrix.target }} --features hazmat
       - env:
-          RUSTFLAGS: "-Dwarnings --cfg aes_force_soft --cfg aes_compact"
+          RUSTFLAGS: '-Dwarnings --cfg aes_backend="soft" --cfg aes_compact'
         run: |
           cargo build --target ${{ matrix.target }}
           cargo build --target ${{ matrix.target }} --features hazmat
@@ -112,7 +112,7 @@ jobs:
         include:
           - target: x86_64-unknown-linux-gnu
             rust: stable
-            RUSTFLAGS: "-Dwarnings --cfg aes_avx256"
+            RUSTFLAGS: '-Dwarnings --cfg aes_backend="avx256"'
     env:
       CARGO_INCREMENTAL: 0
       RUSTFLAGS: ${{ matrix.RUSTFLAGS }}
@@ -150,10 +150,7 @@ jobs:
         include:
           - target: x86_64-unknown-linux-gnu
             rust: stable
-            RUSTFLAGS: "-Dwarnings --cfg aes_avx512"
-          - target: x86_64-unknown-linux-gnu
-            rust: stable
-            RUSTFLAGS: "-Dwarnings --cfg aes_avx256 --cfg aes_avx512"
+            RUSTFLAGS: '-Dwarnings --cfg aes_backend="avx512"'
     env:
       CARGO_INCREMENTAL: 0
       RUSTFLAGS: ${{ matrix.RUSTFLAGS }}
@@ -214,11 +211,11 @@ jobs:
       - run: cargo test --target ${{ matrix.target }} --features hazmat
       - run: cargo test --target ${{ matrix.target }} --all-features
 
-  # Tests for the portable software backend (i.e. `aes_force_soft`-only)
+  # Tests for the portable software backend (i.e. `aes_backend="soft"`-only)
   soft:
     runs-on: ubuntu-latest
     env:
-      RUSTFLAGS: "-Dwarnings --cfg aes_force_soft"
+      RUSTFLAGS: '-Dwarnings --cfg aes_backend="soft"'
     strategy:
       matrix:
         include:
@@ -280,17 +277,17 @@ jobs:
           cross test --package aes --target ${{ matrix.target }}
           cross test --package aes --target ${{ matrix.target }} --features hazmat
       - env:
-          RUSTFLAGS: "-Dwarnings --cfg aes_force_soft"
+          RUSTFLAGS: '-Dwarnings --cfg aes_backend="soft"'
         run: |
           cross test --package aes --target ${{ matrix.target }}
           cross test --package aes --target ${{ matrix.target }} --features hazmat
       - env:
-          RUSTFLAGS: "-Dwarnings --cfg aes_compact"
+          RUSTFLAGS: '-Dwarnings --cfg aes_compact'
         run: |
           cross test --package aes --target ${{ matrix.target }}
           cross test --package aes --target ${{ matrix.target }} --features hazmat
       - env:
-          RUSTFLAGS: "-Dwarnings --cfg aes_force_soft --cfg aes_compact"
+          RUSTFLAGS: '-Dwarnings --cfg aes_backend="soft" --cfg aes_compact'
         run: |
           cross test --package aes --target ${{ matrix.target }}
           cross test --package aes --target ${{ matrix.target }} --features hazmat
@@ -322,7 +319,7 @@ jobs:
 
   clippy:
     env:
-      RUSTFLAGS: "-Dwarnings --cfg aes_compact"
+      RUSTFLAGS: '-Dwarnings --cfg aes_compact'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4

aes/Cargo.toml

@@ -31,9 +31,7 @@ hazmat = [] # Expose cryptographically hazardous APIs
 level = "warn"
 check-cfg = [
     'cfg(aes_compact)',
-    'cfg(aes_force_soft)',
-    'cfg(aes_avx256)',
-    'cfg(aes_avx512)',
+    'cfg(aes_backend, values("soft", "avx256", "avx512"))',
     'cfg(cpubits, values("16", "32", "64"))'
 ]
 

aes/src/hazmat.rs

@@ -17,15 +17,18 @@ pub use crate::Block;
 /// Eight 128-bit AES blocks
 pub type Block8 = cipher::array::Array<Block, cipher::consts::U8>;
 
-#[cfg(all(target_arch = "aarch64", not(aes_force_soft)))]
+#[cfg(all(target_arch = "aarch64", not(aes_backend = "soft")))]
 use crate::armv8::hazmat as intrinsics;
 
-#[cfg(all(any(target_arch = "x86_64", target_arch = "x86"), not(aes_force_soft)))]
+#[cfg(all(
+    any(target_arch = "x86", target_arch = "x86_64"),
+    not(aes_backend = "soft")
+))]
 use crate::x86::ni::hazmat as intrinsics;
 
 #[cfg(all(
     any(target_arch = "x86", target_arch = "x86_64", target_arch = "aarch64"),
-    not(aes_force_soft)
+    not(aes_backend = "soft")
 ))]
 cpufeatures::new!(aes_intrinsics, "aes");
 
@@ -35,7 +38,7 @@ macro_rules! if_intrinsics_available {
     ($body:expr) => {{
         #[cfg(all(
             any(target_arch = "x86", target_arch = "x86_64", target_arch = "aarch64"),
-            not(aes_force_soft)
+            not(aes_backend = "soft")
         ))]
         if aes_intrinsics::get() {
             unsafe { $body }

aes/src/lib.rs

@@ -46,7 +46,7 @@
 //! will ensure that AESNI and VAES are always used.
 //!
 //! Note: Enabling VAES256 or VAES512 still requires specifying `--cfg
-//! aes_avx256` or `--cfg aes_avx512` explicitly.
+//! aes_backend = "avx256"` or `--cfg aes_backend = "avx512"` explicitly.
 //!
 //! Programs built in this manner will crash with an illegal instruction on
 //! CPUs which do not have AES-NI and VAES enabled.
@@ -102,7 +102,10 @@
 //!
 //! You can modify crate using the following configuration flags:
 //!
-//! - `aes_force_soft`: force software implementation.
+//! - `aes_backend`: explicitly select one of the following backends:
+//!   `"soft"`: force software backend
+//!   `"avx256"`: force AVX2 backend
+//!   `"avx512"`: force AVX-512 backend
 //! - `aes_compact`: reduce code size at the cost of slower performance
 //!   (affects only software backend).
 //!
@@ -130,13 +133,13 @@ mod macros;
 mod soft;
 
 cpubits::cfg_if! {
-    if #[cfg(all(target_arch = "aarch64", not(aes_force_soft)))] {
+    if #[cfg(all(target_arch = "aarch64", not(aes_backend = "soft")))] {
         mod armv8;
         mod autodetect;
         pub use autodetect::*;
     } else if #[cfg(all(
         any(target_arch = "x86", target_arch = "x86_64"),
-        not(aes_force_soft)
+        not(aes_backend = "soft")
     ))] {
         mod x86;
         mod autodetect;
@@ -188,7 +191,10 @@ mod tests {
         test_for(soft::Aes256Enc::new(&key_256));
         test_for(soft::Aes256Dec::new(&key_256));
 
-        #[cfg(all(any(target_arch = "x86", target_arch = "x86_64"), not(aes_force_soft)))]
+        #[cfg(all(
+            any(target_arch = "x86", target_arch = "x86_64"),
+            not(aes_backend = "soft")
+        ))]
         {
             use super::x86;
 
@@ -206,7 +212,7 @@ mod tests {
             }
         }
 
-        #[cfg(all(target_arch = "aarch64", not(aes_force_soft)))]
+        #[cfg(all(target_arch = "aarch64", not(aes_backend = "soft")))]
         {
             use super::armv8;