Add support for Nix

Author: emilhem

Makefile

@@ -16,15 +16,15 @@ INCLUDE=include
 # own device app* you just need to include tkey/debug.h and define
 # either of them. You don't need to recompile tkey-libs.
 
-CFLAGS = -target riscv32-unknown-none-elf -march=rv32iczmmul -mabi=ilp32 \
+CFLAGS = $(EXTRA_CFLAGS) -target riscv32-unknown-none-elf -march=rv32iczmmul -mabi=ilp32 \
 	-mcmodel=medany -static -std=gnu99 -O2 -ffast-math -fno-common \
 	-fno-builtin-printf -fno-builtin-putchar -nostdlib -mno-relax -flto \
 	-Wall -Werror=implicit-function-declaration \
 	-I $(INCLUDE) -I .
 
 AS = clang
 AR = llvm-ar
-ASFLAGS = -target riscv32-unknown-none-elf -march=rv32iczmmul -mabi=ilp32 \
+ASFLAGS = $(EXTRA_ASFLAGS) -target riscv32-unknown-none-elf -march=rv32iczmmul -mabi=ilp32 \
 	-mcmodel=medany -mno-relax
 
 LDFLAGS=-T app.lds -L libcommon/ -lcommon -L libcrt0/ -lcrt0

shell.nix

@@ -0,0 +1,25 @@
+with import <nixpkgs> {};
+let
+  # Use unwrapped clang to avoid hardening flags
+  unwrappedClang = clang_multi.cc;
+in
+mkShell {
+  nativeBuildInputs = [
+    gnumake
+    unwrappedClang
+    unwrappedClang.lib
+    llvm
+    lld
+    go
+    pre-commit
+  ];
+
+  # Override CC/AS to use unwrapped clang (avoids Nix hardening wrapper)
+  # Set resource directory for built-in headers (stddef.h, stdint.h, etc.)
+  shellHook = ''
+    export CC="${unwrappedClang}/bin/clang"
+    export AS="${unwrappedClang}/bin/clang"
+    export EXTRA_CFLAGS="-resource-dir ${unwrappedClang.lib}/lib/clang/19"
+    export EXTRA_ASFLAGS="-resource-dir ${unwrappedClang.lib}/lib/clang/19"
+  '';
+}