use overlay instead of passing llvm/rustc/cargo around

Run:
qemu-system-riscv32 -nographic -machine sifive_u -kernel target/riscv32imc-unknown-none-elf/release/helloworld

derivations.nix

@@ -16,18 +16,5 @@ rec {
   heavycomps = pkgs.callPackage ./heavycomps.nix { inherit nmigen; };
 
   binutils-riscv = pkgs.callPackage ./compilers/binutils.nix { platform = "riscv32"; };
-  llvm_7 = pkgs.llvm_7.overrideAttrs(oa: {
-    name = oa.name + "-riscv";
-    cmakeFlags = oa.cmakeFlags ++ ["-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=RISCV"];
-  });
-  rustc = (pkgs.rustc.overrideAttrs(oa: {
-    name = "${oa.pname}-${oa.version}-riscv";
-  })).override {
-    inherit llvm_7;
-    pkgsBuildBuild = pkgs.pkgsBuildBuild // { inherit llvm_7; };
-    pkgsBuildHost = pkgs.pkgsBuildHost // { inherit llvm_7; };
-    pkgsBuildTarget = pkgs.pkgsBuildTarget // { inherit llvm_7; };
-  };
-  rust-riscv32imc-crates = pkgs.callPackage ./compilers/rust-riscv32imc-crates.nix { inherit rustc; };
-  cargo = pkgs.cargo.override { inherit rustc; };
+  rust-riscv32imc-crates = pkgs.callPackage ./compilers/rust-riscv32imc-crates.nix { };
 }

firmware/memory.x

@@ -1,5 +1,5 @@
 MEMORY
 {
-  FLASH : ORIGIN = 0x20000000, LENGTH = 16M
-  RAM : ORIGIN = 0x80000000, LENGTH = 16K
+  FLASH : ORIGIN = 0x80000000, LENGTH = 16M
+  RAM : ORIGIN = 0x81000000, LENGTH = 16K
 }

firmware/src/main.rs

@@ -8,5 +8,11 @@ use riscv_rt::entry;
 
 #[entry]
 fn main() -> ! {
-    loop {}
+    let foo = "hello world\n";
+    loop {
+        for c in foo.chars() {
+            let mem = 0x1001_3000 as *mut u8;
+            unsafe { *mem = c as u8 }
+        }
+    }
 }

overlay.nix

@@ -0,0 +1,7 @@
+self: super:
+{
+  llvm_7 = super.llvm_7.overrideAttrs(oa: {
+    name = oa.name + "-riscv";
+    cmakeFlags = oa.cmakeFlags ++ ["-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=RISCV"];
+  });
+}

release.nix

@@ -1,7 +1,12 @@
-{ pkgs ? import <nixpkgs> {}}:
+{ }:
 let
+  pkgs = import <nixpkgs> { overlays = [ import ./overlay.nix ]; };
   derivations = import ./derivations.nix { inherit pkgs; };
   jobs = derivations // {
+    rustc = pkgs.rustc;
+    cargo = pkgs.cargo;
+    cargo-vendor = pkgs.cargo-vendor;
+
     helloworld_ecp5 = import ./examples/helloworld_ecp5.nix { inherit pkgs; };
     helloworld_kintex7 = import ./examples/helloworld_kintex7.nix { inherit pkgs; };
     simplesoc_ecp5 = import ./examples/simplesoc_ecp5.nix { inherit pkgs; };

shell-firmware.nix

@@ -1,5 +1,6 @@
-{ pkgs ? import <nixpkgs> {}}:
+{ }:
 let
+  pkgs = import <nixpkgs> { overlays = [ import ./overlay.nix ]; };
   hx = import ./derivations.nix { inherit pkgs; };
 in
   pkgs.mkShell {