From c9fc4a420ccbda8fa01787da751685802556ee85 Mon Sep 17 00:00:00 2001
From: Konstantin Nazarov <mail@knazarov.com>
Date: Fri, 6 Dec 2024 22:40:52 +0000
Subject: [PATCH] Add an example program in C

---
 .gitignore        |  3 ++-
 example/Makefile  |  2 ++
 example/example.c |  9 +++++++++
 example/linker.ld | 19 +++++++++++++++++++
 flake.nix         | 14 ++++++++++----
 rve.nix           | 12 ++++++++++--
 src/rve.cpp       |  2 +-
 7 files changed, 53 insertions(+), 8 deletions(-)
 create mode 100644 example/Makefile
 create mode 100644 example/example.c
 create mode 100644 example/linker.ld

diff --git a/.gitignore b/.gitignore
index 2b050c3..6b7083d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,4 +17,5 @@ CMakeCache.txt
 CTestTestfile.cmake
 Testing
 result
-build
\ No newline at end of file
+build
+example/example
\ No newline at end of file
diff --git a/example/Makefile b/example/Makefile
new file mode 100644
index 0000000..57666ed
--- /dev/null
+++ b/example/Makefile
@@ -0,0 +1,2 @@
+example: example.c
+	riscv32-none-elf-gcc -fno-builtin -fvisibility=hidden -nostdlib -nostartfiles -march=rv32im -mabi=ilp32 -o example example.c -T linker.ld
diff --git a/example/example.c b/example/example.c
new file mode 100644
index 0000000..460520c
--- /dev/null
+++ b/example/example.c
@@ -0,0 +1,9 @@
+static int mem;
+
+int main() {
+  int a = 42;
+  int b = 5;
+  mem = a*b + 3;
+
+  return 0;
+}
diff --git a/example/linker.ld b/example/linker.ld
new file mode 100644
index 0000000..a5ea337
--- /dev/null
+++ b/example/linker.ld
@@ -0,0 +1,19 @@
+ENTRY(_start)
+
+SECTIONS {
+    . = 0x1000;  /* Start address of the program */
+
+    .text : {
+        *(.text)   /* Place all .text sections (code) here */
+    }
+
+    .data : {
+        *(.data)   /* Place all .data sections (initialized data) here */
+    }
+
+    .bss : {
+        *(.bss)    /* Place all .bss sections (uninitialized data) here */
+    }
+
+    /DISCARD/ : { *(.note.GNU-stack) }  /* Discard stack section */
+}
diff --git a/flake.nix b/flake.nix
index 9e06636..6e2312b 100644
--- a/flake.nix
+++ b/flake.nix
@@ -21,16 +21,22 @@
       forAllSystems = f: nixpkgs.lib.genAttrs allSystems (system: f {
         pkgs = import nixpkgs { inherit system; };
       });
+      riscv-pkgs = import nixpkgs {
+        localSystem = "x86_64-linux";
+        crossSystem = {
+          config = "riscv32-unknown-linux-gnu";
+        };
+      };
     in
       {
-        packages = forAllSystems( {pkgs }:
+        packages = forAllSystems( {pkgs}:
           {
-            lisp = (pkgs.callPackage ./rve.nix {});
-            default = (pkgs.callPackage ./rve.nix {});
+            lisp = (pkgs.callPackage ./rve.nix {riscv-pkgs=riscv-pkgs;});
+            default = (pkgs.callPackage ./rve.nix {riscv-pkgs=riscv-pkgs;});
           }
         );
         overlays.default = final: prev: {
-          lisp = (prev.callPackage ./rve.nix {});
+          lisp = (prev.callPackage ./rve.nix {riscv-pkgs=riscv-pkgs;});
         };
       };
 }
diff --git a/rve.nix b/rve.nix
index 0608629..6be2130 100644
--- a/rve.nix
+++ b/rve.nix
@@ -1,4 +1,4 @@
-{ pkgs, stdenv }:
+{ pkgs, stdenv, riscv-pkgs }:
 pkgs.gcc13Stdenv.mkDerivation rec {
   pname = "rve";
   version = "0.1.0";
@@ -13,7 +13,15 @@ pkgs.gcc13Stdenv.mkDerivation rec {
 
   nativeBuildInputs = with pkgs; [ pkg-config cmake ninja ];
 
-  buildInputs = with pkgs; [ gdb linuxPackages.perf jq lcov ];
+  buildInputs = with pkgs; [
+    gdb
+    linuxPackages.perf
+    jq
+    lcov
+    #riscv-pkgs.buildPackages.gcc
+    pkgsCross.riscv32-embedded.buildPackages.gcc
+    pkgsCross.riscv32-embedded.buildPackages.binutils
+  ];
 
   hardeningDisable = [ "all" ];
   cmakeFlags = [
diff --git a/src/rve.cpp b/src/rve.cpp
index 92be719..d179de5 100644
--- a/src/rve.cpp
+++ b/src/rve.cpp
@@ -5,7 +5,7 @@
 #include <cstring>
 
 int main() {
-  const size_t MEMORY_SIZE = 1024;
+  const size_t MEMORY_SIZE = 128*1024;
   uint8_t memory[MEMORY_SIZE] = {0};
 
   uint32_t program[] = {