diff --git a/flake.lock b/flake.lock
index 99b33d00..14a262b1 100644
--- a/flake.lock
+++ b/flake.lock
@@ -35,42 +35,27 @@
         "type": "github"
       }
     },
-    "flake-utils_2": {
-      "inputs": {
-        "systems": "systems_2"
-      },
-      "locked": {
-        "lastModified": 1701680307,
-        "narHash": "sha256-kAuep2h5ajznlPMD9rnQyffWG8EM/C73lejGofXvdM8=",
-        "owner": "numtide",
-        "repo": "flake-utils",
-        "rev": "4022d587cbbfd70fe950c1e2083a02621806a725",
-        "type": "github"
-      },
-      "original": {
-        "owner": "numtide",
-        "repo": "flake-utils",
-        "type": "github"
-      }
-    },
     "lowrisc-nix": {
       "inputs": {
-        "flake-utils": "flake-utils_2",
+        "flake-utils": [
+          "flake-utils"
+        ],
         "nixpkgs": [
           "nixpkgs"
         ],
         "poetry2nix": "poetry2nix"
       },
       "locked": {
-        "lastModified": 1703264099,
-        "narHash": "sha256-sgSNitlXAMblPTsV8uCguIn1LD0zeANRHv2BjZx5THo=",
+        "lastModified": 1703159561,
+        "narHash": "sha256-EFLITT8uzdCRsaW0FL+fgDLgQzJlyemJUOkjtnOKlfM=",
         "owner": "lowRISC",
         "repo": "lowrisc-nix",
-        "rev": "81a1467706e01077ee60cba8448594a7ea672b35",
+        "rev": "f12db37b69b4fc531c047636b2a1e7882bea7de4",
         "type": "github"
       },
       "original": {
         "owner": "lowRISC",
+        "ref": "pull/4/merge",
         "repo": "lowrisc-nix",
         "type": "github"
       }
@@ -124,7 +109,7 @@
           "lowrisc-nix",
           "nixpkgs"
         ],
-        "systems": "systems_3",
+        "systems": "systems_2",
         "treefmt-nix": "treefmt-nix"
       },
       "locked": {
@@ -165,21 +150,6 @@
       }
     },
     "systems_2": {
-      "locked": {
-        "lastModified": 1681028828,
-        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
-        "owner": "nix-systems",
-        "repo": "default",
-        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nix-systems",
-        "repo": "default",
-        "type": "github"
-      }
-    },
-    "systems_3": {
       "locked": {
         "lastModified": 1681028828,
         "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
diff --git a/flake.nix b/flake.nix
index aaefab95..bb45aba8 100644
--- a/flake.nix
+++ b/flake.nix
@@ -5,8 +5,9 @@
     nixpkgs.url = "github:nixos/nixpkgs/nixos-23.11";
     flake-utils.url = "github:numtide/flake-utils";
     lowrisc-nix = {
-      url = "github:lowRISC/lowrisc-nix";
+      url = "github:lowRISC/lowrisc-nix/pull/4/merge";
       inputs.nixpkgs.follows = "nixpkgs";
+      inputs.flake-utils.follows = "flake-utils";
     };
     deps = {
       url = "path:./dependencies";
@@ -30,6 +31,9 @@
             # Add extra packages we might need
             # Currently this contains the lowrisc riscv-toolchain, and spike
             deps.overlay_pkgs
+            (final: prev: {
+              inherit (inputs.lowrisc-nix.packages.${system}) lowrisc-toolchain-gcc-rv32imcb;
+            })
           ];
         };
 
@@ -62,7 +66,15 @@
             zlib
             # vivado
           ]);
+
+        rules = import ./rules {inherit pkgs;};
       in {
+        legacyPackages.sw = let
+          common = pkgs.callPackage sw/c/common {inherit rules;};
+          demo = pkgs.callPackage sw/c/demo {inherit rules common;};
+        in {
+          inherit common demo;
+        };
         devShells.default = pkgs.mkShell {
           name = "labenv";
           buildInputs = project_deps;
diff --git a/rules/cc.nix b/rules/cc.nix
new file mode 100644
index 00000000..b5c55756
--- /dev/null
+++ b/rules/cc.nix
@@ -0,0 +1,175 @@
+{
+  pkgs,
+  lib,
+  stdenv,
+  toolchain ? {
+    cc = "/no-toolchain-defined";
+    cflags = [];
+    ld = "/no-toolchain-defined";
+    ldflags = [];
+    asm = "/no-toolchain-defined";
+    asmflags = [];
+  },
+}: let
+  include = {
+    src,
+    deps ? [],
+  }:
+    pkgs.runCommandLocal (builtins.baseNameOf src) {} ''
+      mkdir -p $out/include
+
+      ARGS=()
+      for dep in $deps; do
+        if [ -d $dep/include ]; then
+          ln -s $src/include/* $out/include/
+        fi
+      done
+
+      ln -s ${src} $out/include/${builtins.baseNameOf src}
+    '';
+
+  # If a raw file path is specified, turn that into a header derivation.
+  autowrap_header = f:
+    if !(builtins.isPath f)
+    then f
+    else if lib.hasSuffix ".h" f
+    then include {src = f;}
+    else throw "unknown file type: ${f}";
+
+  # Turn all raw file paths into derivations.
+  # Files will be grouped so that source files can depend on header files.
+  autowrap_deps = deps: let
+    src = builtins.filter (f: builtins.isPath f && !(lib.hasSuffix ".h" f)) deps;
+    other = builtins.filter (f: !(builtins.isPath f) || lib.hasSuffix ".h" f) deps;
+    wrapped = map autowrap_header other;
+    src_drv =
+      map (
+        f:
+          if lib.hasSuffix ".S" f
+          then
+            asm {
+              src = f;
+              deps = wrapped;
+            }
+          else if lib.hasSuffix ".c" f
+          then
+            object {
+              src = f;
+              deps = wrapped;
+            }
+          else throw "unknown file type: ${f}"
+      )
+      src;
+  in
+    src_drv ++ wrapped;
+
+  asm = {
+    src,
+    deps ? [],
+    extra-asmflags ? [],
+    asmflags ? toolchain.asmflags ++ extra-asmflags,
+  }:
+    stdenv.mkDerivation {
+      name = (lib.removeSuffix ".S" (builtins.baseNameOf src)) + ".o";
+      inherit src asmflags;
+      inherit (toolchain) asm;
+      deps = autowrap_deps deps;
+      dontUnpack = true;
+      buildPhase = ''
+        ARGS=()
+        for dep in $deps; do
+          if [ -d $dep/include ]; then
+            ARGS+=(-I$dep/include)
+          fi
+        done
+
+        mkdir -p $out/obj
+        $asm $asmflags -c -o $out/obj/$name $src ''${ARGS[@]}
+      '';
+    };
+
+  object = {
+    src,
+    deps ? [],
+    extra-cflags ? [],
+    cflags ? toolchain.cflags ++ extra-cflags,
+  }:
+    stdenv.mkDerivation {
+      name = (lib.removeSuffix ".c" (builtins.baseNameOf src)) + ".o";
+      inherit src cflags;
+      inherit (toolchain) cc;
+      deps = autowrap_deps deps;
+      dontUnpack = true;
+      buildPhase = ''
+        ARGS=()
+        for dep in $deps; do
+          if [ -d $dep/include ]; then
+            ARGS+=(-I$dep/include)
+          fi
+        done
+
+        mkdir -p $out/obj
+        $cc $cflags -c -o $out/obj/$name $src ''${ARGS[@]}
+      '';
+    };
+
+  static = {
+    name,
+    deps,
+  }:
+    stdenv.mkDerivation {
+      inherit name;
+      srcs = autowrap_deps deps;
+      dontUnpack = true;
+      buildPhase = ''
+        ARGS=()
+        for src in $srcs; do
+          if [ -d $src/obj ]; then
+            ARGS+=($src/obj/*)
+          fi
+          if [ -d $src/include ]; then
+            mkdir -p $out/include
+            ln -s $src/include/* $out/include/
+          fi
+        done
+
+        mkdir -p $out/lib
+        ar rcs $out/lib/$name ''${ARGS[@]}
+      '';
+    };
+
+  binary = {
+    name,
+    deps ? [],
+    extra-ldflags ? [],
+    ldflags ? toolchain.ldflags ++ extra-ldflags,
+  }:
+    stdenv.mkDerivation {
+      inherit name ldflags;
+      inherit (toolchain) ld;
+      srcs = autowrap_deps deps;
+      dontUnpack = true;
+      buildPhase = ''
+        ARGS=()
+        for src in $srcs; do
+          if [ -d $src/obj ]; then
+            ARGS+=($src/obj/*)
+          fi
+          if [ -d $src/lib ]; then
+            ARGS+=($src/lib/*)
+          fi
+        done
+
+        mkdir -p $out/bin
+        $ld $ldflags -o $out/bin/$name ''${ARGS[@]}
+      '';
+    };
+
+  set = deps:
+    pkgs.symlinkJoin {
+      name = "";
+      paths = autowrap_deps deps;
+    };
+in {
+  inherit asm include object static binary set;
+}
diff --git a/rules/default.nix b/rules/default.nix
new file mode 100644
index 00000000..48982fe1
--- /dev/null
+++ b/rules/default.nix
@@ -0,0 +1,3 @@
+{pkgs}: {
+  cc = pkgs.callPackage ./cc.nix {};
+}
diff --git a/sw/c/common/default.nix b/sw/c/common/default.nix
new file mode 100644
index 00000000..75548ac2
--- /dev/null
+++ b/sw/c/common/default.nix
@@ -0,0 +1,64 @@
+{
+  rules,
+  pkgs,
+  lowrisc-toolchain-gcc-rv32imcb,
+}: let
+  toolchain = rec {
+    cc = "${lowrisc-toolchain-gcc-rv32imcb}/bin/riscv32-unknown-elf-gcc";
+    cflags = ["-march=rv32imc" "-mabi=ilp32" "-mcmodel=medany" "-Wall" "-fvisibility=hidden" "-ffreestanding"];
+    ld = cc;
+    ldflags = ["-nostartfiles" "-T" "${../../common/link.ld}"];
+    asm = cc;
+    asmflags = ["-march=rv32imc"];
+  };
+
+  rules_cc = rules.cc.override {
+    inherit toolchain;
+  };
+
+  passthru = with rules_cc; rec {
+    inherit toolchain rules_cc;
+
+    crt0 = asm {
+      src = ./crt0.S;
+      deps = [./demo_system_regs.h];
+    };
+
+    gpio = object {
+      src = ./gpio.c;
+      deps = [./gpio.h ./uart.h ./dev_access.h ./demo_system.h ./demo_system_regs.h];
+      extra-cflags = ["-O3"];
+    };
+
+    uart = object {
+      src = ./uart.c;
+      deps = [./gpio.h ./uart.h ./dev_access.h ./demo_system.h ./demo_system_regs.h];
+    };
+
+    pwm = object {
+      src = ./pwm.c;
+      deps = [./gpio.h ./uart.h ./pwm.h ./dev_access.h ./demo_system.h ./demo_system_regs.h];
+    };
+
+    spi = object {
+      src = ./spi.c;
+      deps = [./gpio.h ./uart.h ./spi.h ./dev_access.h ./demo_system.h ./demo_system_regs.h];
+    };
+
+    timer = object {
+      src = ./timer.c;
+      deps = [./gpio.h ./uart.h ./timer.h ./dev_access.h ./demo_system.h ./demo_system_regs.h];
+    };
+
+    demo_system = object {
+      src = ./demo_system.c;
+      deps = [./gpio.h ./uart.h ./dev_access.h ./demo_system.h ./demo_system_regs.h];
+    };
+
+    common = static {
+      name = "common.a";
+      deps = [crt0 gpio uart pwm spi timer ./demo_system.c] ++ [./gpio.h ./uart.h ./timer.h ./spi.h ./pwm.h ./dev_access.h ./demo_system.h ./demo_system_regs.h];
+    };
+  };
+in
+  passthru.common // passthru
diff --git a/sw/c/demo/default.nix b/sw/c/demo/default.nix
new file mode 100644
index 00000000..1d8a2158
--- /dev/null
+++ b/sw/c/demo/default.nix
@@ -0,0 +1,11 @@
+{
+  rules,
+  common,
+  lowrisc-toolchain-gcc-rv32imcb,
+}:
+with common.rules_cc; {
+  hello_world = binary {
+    name = "hello_world";
+    deps = [hello_world/main.c common];
+  };
+}