fix: build.rs now selects accelerated backend for xous

curve25519-dalek/Cargo.toml

@@ -58,9 +58,9 @@ zeroize = { version = "1", default-features = false, optional = true }
 
 # Betrusted/Precursor dependency set
 [target.'cfg(curve25519_dalek_backend = "u32e_backend")'.dependencies]
-engine25519-as = {git = "https://github.com/betrusted-io/engine25519-as.git", rev = "d249c967556b02ab5439eacb5078fa00c60b93d6", default-features = false, features = [], optional = true}
+engine25519-as = {git = "https://github.com/betrusted-io/engine25519-as.git", rev = "d249c967556b02ab5439eacb5078fa00c60b93d6", default-features = false, features = []}
-engine-25519 = { git = "https://github.com/betrusted-io/xous-engine-25519.git", rev = "63d3d1f30736022e791deaacf4dd62c00b42fe2e", optional = true}
+engine-25519 = { git = "https://github.com/betrusted-io/xous-engine-25519.git", rev = "63d3d1f30736022e791deaacf4dd62c00b42fe2e"}
-utralib = {version = "0.1.0", optional = true} # this is bogus -- must be patched in the invoking build environment TODO: if this builds, it seems a crate has been released as version 0.1.23 that could replace this
+utralib = {version = "0.1.0"} # this is bogus -- must be patched in the invoking build environment TODO: if this builds, it seems a crate has been released as version 0.1.23 that could replace this
 
 [target.'cfg(target_arch = "x86_64")'.dependencies]
 cpufeatures = "0.2.6"
@@ -76,5 +76,5 @@ legacy_compatibility = []
 group = ["dep:group", "rand_core"]
 group-bits = ["group", "ff/bits"]
 
-[target.'cfg(all(not(curve25519_dalek_backend = "fiat"), not(curve25519_dalek_backend = "serial"), target_arch = "x86_64"))'.dependencies]
+[target.'cfg(all(not(curve25519_dalek_backend = "fiat"), not(curve25519_dalek_backend = "serial"), target_arch = "x86_64", not(curve25519_dalek_backend = "u32e_backend")))'.dependencies]
 curve25519-dalek-derive = { version = "0.1", path = "../curve25519-dalek-derive" }

curve25519-dalek/build.rs

@@ -2,6 +2,9 @@
 
 #![deny(clippy::unwrap_used, dead_code)]
 
+use platforms::Platform;
+use platforms::target;
+
 #[allow(non_camel_case_types)]
 #[derive(PartialEq, Debug)]
 enum DalekBits {
@@ -10,6 +13,9 @@ enum DalekBits {
 }
 
 fn main() {
+    let target_triplet = std::env::var("TARGET").unwrap();
+    let platform = platforms::Platform::find(&target_triplet).unwrap();
+    //Xous running on 
     let curve25519_dalek_bits = match std::env::var("CARGO_CFG_CURVE25519_DALEK_BITS").as_deref() {
         Ok("32") => DalekBits::Dalek32,
         Ok("64") => DalekBits::Dalek64,
@@ -54,12 +60,22 @@ fn main() {
                     // See: issues/532
                     false => panic!("Could not override curve25519_dalek_backend to simd"),
                 }
-            }
-            // default between serial / simd (if potentially capable)
-            _ => match is_capable_simd(&target_arch, curve25519_dalek_bits) {
-                true => "simd",
-                false => "serial",
             },
+            //coprocessor for Precursor
+            Ok("u32e_backend") => {
+                if curve25519_dalek_bits != DalekBits::Dalek64{
+                    panic!("u32e_backend only supports 32 bit bits");
+                }
+                "u32e_backend"
+            },
+            // default between serial / simd (if potentially capable)
+            _ => match is_precursor(platform) {
+                true => "u32e_backend",
+                false => match is_capable_simd(&target_arch, curve25519_dalek_bits) {
+                    true => "simd",
+                    false => "serial",
+                },
+            }
         };
     println!("cargo:rustc-cfg=curve25519_dalek_backend=\"{curve25519_dalek_backend}\"");
 }
@@ -68,6 +84,10 @@ fn main() {
 fn is_capable_simd(arch: &str, bits: DalekBits) -> bool {
     arch == "x86_64" && bits == DalekBits::Dalek64
 }
+// Is the target the Precursor?
+fn is_precursor(platform: &Platform) -> bool {
+    platform.target_os == target::OS::Xous && platform.target_arch == target::Arch::Riscv32
+}
 
 // Deterministic cfg(curve25519_dalek_bits) when this is not explicitly set.
 mod deterministic {

curve25519-dalek/src/backend/serial/u32e/constants.rs

@@ -11,11 +11,11 @@
 
 //! This module contains backend-specific constant values, such as the 64-bit limbs of curve constants.
 
-use backend::serial::curve_models::AffineNielsPoint;
+use crate::backend::serial::curve_models::AffineNielsPoint;
 use super::field::Engine25519;
 use super::scalar::Scalar29;
-use edwards::{EdwardsBasepointTable, EdwardsPoint};
+use crate::edwards::{EdwardsBasepointTable, EdwardsPoint};
-use window::{LookupTable, NafLookupTable8};
+use crate::window::{LookupTable, NafLookupTable8};
 
 /// The value of minus one, equal to `-&FieldElement::one()`
 pub(crate) const MINUS_ONE: Engine25519 = Engine25519([

curve25519-dalek/src/backend/serial/u32e/scalar.rs

@@ -14,7 +14,7 @@ use core::ops::{Index, IndexMut};
 
 use zeroize::Zeroize;
 
-use constants;
+use crate::constants;
 
 /// The `Scalar29` struct represents an element in ℤ/lℤ as 9 29-bit limbs
 #[derive(Copy,Clone)]

curve25519-dalek/src/scalar.rs

@@ -159,7 +159,7 @@ cfg_if! {
         /// module.
         //TODO: this should be the same as the u32 backend such that we don't even need to have
         //backend/serial/scalar.rs defined. Double check that to simplify the code. 
-        type UnpackedScalar = backend::serial::u32::scalar::Scalar29;
+        type UnpackedScalar = backend::serial::u32e::scalar::Scalar29;
     }
     else if #[cfg(curve25519_dalek_backend = "fiat")] {
         /// An `UnpackedScalar` represents an element of the field GF(l), optimized for speed.