commit 13bc0fc2f9f9d5e59922fd7c4960b0303316ccc1
Author: Michael Zhang <mail@mzhang.io>
Date:   Sat Feb 4 03:13:22 2023 -0600

    Initial

diff --git a/.envrc b/.envrc
new file mode 100644
index 0000000..3550a30
--- /dev/null
+++ b/.envrc
@@ -0,0 +1 @@
+use flake
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..0673277
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+/target
+.direnv
+
+result*
+*.o
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..5510e9d
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,390 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "anyhow"
+version = "1.0.68"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2cb2f989d18dd141ab8ae82f64d1a8cdd37e0840f73a406896cf5e99502fab61"
+
+[[package]]
+name = "bitflags"
+version = "1.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
+
+[[package]]
+name = "cc"
+version = "1.0.79"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "50d30906286121d95be3d479533b458f87493b30a4b5f79a607db8f5d11aa91f"
+
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
+[[package]]
+name = "clap"
+version = "4.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f13b9c79b5d1dd500d20ef541215a6423c75829ef43117e1b4d17fd8af0b5d76"
+dependencies = [
+ "bitflags",
+ "clap_derive",
+ "clap_lex",
+ "is-terminal",
+ "once_cell",
+ "strsim",
+ "termcolor",
+]
+
+[[package]]
+name = "clap_derive"
+version = "4.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "684a277d672e91966334af371f1a7b5833f9aa00b07c84e92fbce95e00208ce8"
+dependencies = [
+ "heck",
+ "proc-macro-error",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "clap_lex"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "783fe232adfca04f90f56201b26d79682d4cd2625e0bc7290b95123afe558ade"
+dependencies = [
+ "os_str_bytes",
+]
+
+[[package]]
+name = "errno"
+version = "0.2.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f639046355ee4f37944e44f60642c6f3a7efa3cf6b78c78a0d989a8ce6c396a1"
+dependencies = [
+ "errno-dragonfly",
+ "libc",
+ "winapi",
+]
+
+[[package]]
+name = "errno-dragonfly"
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa68f1b12764fab894d2755d2518754e71b4fd80ecfb822714a1206c2aab39bf"
+dependencies = [
+ "cc",
+ "libc",
+]
+
+[[package]]
+name = "goblin"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "572564d6cba7d09775202c8e7eebc4d534d5ae36578ab402fb21e182a0ac9505"
+dependencies = [
+ "log",
+ "plain",
+ "scroll",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
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+
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+
+[[package]]
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+checksum = "1abeb7a0dd0f8181267ff8adc397075586500b81b28a73e8a0208b00fc170fb3"
+dependencies = [
+ "libc",
+ "windows-sys",
+]
+
+[[package]]
+name = "is-terminal"
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+checksum = "22e18b0a45d56fe973d6db23972bf5bc46f988a4a2385deac9cc29572f09daef"
+dependencies = [
+ "hermit-abi",
+ "io-lifetimes",
+ "rustix",
+ "windows-sys",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
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+
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+
+[[package]]
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+dependencies = [
+ "cfg-if",
+]
+
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+ "syn",
+ "version_check",
+]
+
+[[package]]
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+dependencies = [
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+ "quote",
+ "version_check",
+]
+
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+]
+
+[[package]]
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+ "bitflags",
+ "errno",
+ "io-lifetimes",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys",
+]
+
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+ "winapi-i686-pc-windows-gnu",
+ "winapi-x86_64-pc-windows-gnu",
+]
+
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+name = "winapi-i686-pc-windows-gnu"
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+dependencies = [
+ "windows_aarch64_gnullvm",
+ "windows_aarch64_msvc",
+ "windows_i686_gnu",
+ "windows_i686_msvc",
+ "windows_x86_64_gnu",
+ "windows_x86_64_gnullvm",
+ "windows_x86_64_msvc",
+]
+
+[[package]]
+name = "windows_aarch64_gnullvm"
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+
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+
+[[package]]
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+
+[[package]]
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+version = "0.42.1"
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+checksum = "628bfdf232daa22b0d64fdb62b09fcc36bb01f05a3939e20ab73aaf9470d0463"
+
+[[package]]
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+version = "0.42.1"
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diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..9ecf27e
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "riscv64-emulator"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+anyhow = "1.0.68"
+clap = { version = "4.1.4", features = ["derive"] }
+goblin = "0.6.0"
+scroll = "0.11.0"
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..4ca9bb7
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,4 @@
+CC := riscv64-unknown-linux-gnu-gcc
+
+main.o: main.c
+	$(CC) -o $@ $<
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..2dd3492
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,93 @@
+{
+  "nodes": {
+    "fenix": {
+      "inputs": {
+        "nixpkgs": "nixpkgs",
+        "rust-analyzer-src": "rust-analyzer-src"
+      },
+      "locked": {
+        "lastModified": 1675405418,
+        "narHash": "sha256-5Tvd/8kFl+jQ+uYqam/Q1ZRWLNrkF97zRX/l0pUitpU=",
+        "owner": "nix-community",
+        "repo": "fenix",
+        "rev": "8d7682dba94f6a3ad9370d17a4092addcbb23544",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "fenix",
+        "type": "github"
+      }
+    },
+    "flake-utils": {
+      "locked": {
+        "lastModified": 1667395993,
+        "narHash": "sha256-nuEHfE/LcWyuSWnS8t12N1wc105Qtau+/OdUAjtQ0rA=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "5aed5285a952e0b949eb3ba02c12fa4fcfef535f",
+        "type": "github"
+      },
+      "original": {
+        "id": "flake-utils",
+        "type": "indirect"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1675183161,
+        "narHash": "sha256-Zq8sNgAxDckpn7tJo7V1afRSk2eoVbu3OjI1QklGLNg=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "e1e1b192c1a5aab2960bf0a0bd53a2e8124fa18e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs_2": {
+      "locked": {
+        "lastModified": 1667629849,
+        "narHash": "sha256-P+v+nDOFWicM4wziFK9S/ajF2lc0N2Rg9p6Y35uMoZI=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "3bacde6273b09a21a8ccfba15586fb165078fb62",
+        "type": "github"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "fenix": "fenix",
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs_2"
+      }
+    },
+    "rust-analyzer-src": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1675345086,
+        "narHash": "sha256-Y7VnQlwTckCG4ia1zHSxF1mYKfNjfWUlzRyoLTbLn5U=",
+        "owner": "rust-lang",
+        "repo": "rust-analyzer",
+        "rev": "04850a192cd82f94ddbd3f4b202d0e4ea3e62daa",
+        "type": "github"
+      },
+      "original": {
+        "owner": "rust-lang",
+        "ref": "nightly",
+        "repo": "rust-analyzer",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..6c85168
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,33 @@
+{
+  inputs = { fenix.url = "github:nix-community/fenix"; };
+
+  outputs = { self, nixpkgs, flake-utils, fenix }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+          overlays = [ fenix.overlays.default ];
+        };
+
+        toolchain = pkgs.fenix.stable;
+
+        targetPkgs = pkgs.pkgsCross.riscv64;
+      in rec {
+        legacyPackages = pkgs;
+
+        devShell = pkgs.mkShell {
+          inputsFrom = [ ];
+
+          packages = (with pkgs; [
+            cargo-watch
+            cargo-deny
+            cargo-edit
+
+            targetPkgs.stdenv.cc
+            (qemu.override {
+              hostCpuTargets = [ "${targetPkgs.system}-user" ];
+            })
+          ]) ++ (with toolchain; [ cargo rustc rustfmt clippy ]);
+        };
+      });
+}
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..9b216a5
--- /dev/null
+++ b/main.c
@@ -0,0 +1,5 @@
+#include <stdio.h>
+
+int main() {
+    printf("Hello, world!\n");
+}
diff --git a/rustfmt.toml b/rustfmt.toml
new file mode 100644
index 0000000..4c1eefa
--- /dev/null
+++ b/rustfmt.toml
@@ -0,0 +1,2 @@
+max_width = 80
+tab_spaces = 2
diff --git a/src/emulator.rs b/src/emulator.rs
new file mode 100644
index 0000000..97766d9
--- /dev/null
+++ b/src/emulator.rs
@@ -0,0 +1,102 @@
+use std::collections::HashMap;
+
+use anyhow::Result;
+use goblin::elf::Elf;
+use scroll::{Endian, Pread};
+
+// IMPORTANT PAGES IN THE RISC-V SPEC
+// https://riscv.org/wp-content/uploads/2017/05/riscv-spec-v2.2.pdf
+//
+// - 103 (Ch. 19) - Instruction Set Listings (Opcodes)
+
+use crate::instruction::Instruction;
+
+pub type Address = u64;
+
+pub struct Emulator<'a> {
+  contents: &'a [u8],
+  elf: Elf<'a>,
+  endianness: Endian,
+
+  program_counter: u64,
+  registers: [u64; 32],
+  memory_map: HashMap<Address, &'a [u8]>,
+}
+
+impl<'a> Emulator<'a> {
+  pub fn new(contents: &'a [u8]) -> Result<Self> {
+    let elf = Elf::parse(&contents)?;
+    let endianness = elf.header.endianness()?;
+    Ok(Emulator {
+      contents,
+      elf,
+      endianness,
+
+      program_counter: 0,
+      registers: [0; 32],
+      memory_map: HashMap::new(),
+    })
+  }
+
+  pub fn run(&mut self) -> Result<()> {
+    // Set up memory segments
+    for program_header in self.elf.program_headers.iter() {
+      let start = program_header.p_offset as usize;
+      let end = start + program_header.p_memsz as usize;
+      let memory_slice = &self.contents[start..end];
+      self.memory_map.insert(program_header.p_vaddr, memory_slice);
+    }
+
+    println!("Elf entrypoint: 0x{:x?}", self.elf.entry);
+    self.program_counter = self.elf.entry;
+
+    self.step()?;
+    self.step()?;
+
+    Ok(())
+  }
+
+  fn step(&mut self) -> Result<()> {
+    let instruction = self.decode_instruction_at(self.program_counter)?;
+    self.program_counter += instruction.len as u64;
+    Ok(())
+  }
+
+  fn decode_instruction_at(&self, addr: Address) -> Result<Instruction> {
+    let data = self.read_memory_at(addr, 2).unwrap();
+    let data_num = data.pread_with::<u16>(0, self.endianness)?;
+
+    // If the instruction has 11 at the end, it's longer
+    if data_num & 0b11 == 0b11 {
+      let data = self.read_memory_at(addr, 4).unwrap();
+      let data_num = data.pread_with::<u32>(0, self.endianness)?;
+      println!("{:b}", data_num);
+
+      // TODO: If the instruction ends with 11111, it's longer
+
+      // JAL
+      if data_num & 0b1111111 == 0b1101111 {
+        return Ok(Instruction { len: 4 });
+      }
+    } else {
+      println!("{:b}", data_num);
+    }
+
+    todo!()
+  }
+
+  /// Read n bytes from addr
+  // TODO: Could speed this up massively
+  fn read_memory_at(&self, addr: Address, n: usize) -> Option<&[u8]> {
+    for (memory_addr, memory_slice) in self.memory_map.iter() {
+      if addr >= *memory_addr && addr < memory_addr + memory_slice.len() as u64
+      {
+        let start = (addr - *memory_addr) as usize;
+        let end = (start + n) as usize;
+        return Some(&memory_slice[start..end]);
+      }
+    }
+
+    None
+  }
+}
diff --git a/src/instruction.rs b/src/instruction.rs
new file mode 100644
index 0000000..73eb71b
--- /dev/null
+++ b/src/instruction.rs
@@ -0,0 +1,8 @@
+#[derive(Debug)]
+pub struct Instruction {
+  /// The number of bytes in this instruction
+  pub len: usize,
+}
+
+#[derive(Debug)]
+pub enum Op {}
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..04c93ef
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,34 @@
+mod emulator;
+mod instruction;
+
+use std::fs::File;
+use std::io::Read;
+use std::path::PathBuf;
+
+use anyhow::Result;
+use clap::Parser;
+
+use crate::emulator::Emulator;
+
+#[derive(Debug, Parser)]
+struct Opt {
+  input_path: PathBuf,
+}
+
+fn main() -> Result<()> {
+  let opt = Opt::parse();
+
+  println!("Hello, world! {opt:?}");
+
+  let contents = {
+    let mut contents = Vec::new();
+    let mut file = File::open(&opt.input_path)?;
+    file.read_to_end(&mut contents)?;
+    contents
+  };
+
+  let mut emulator = Emulator::new(&contents)?;
+  emulator.run()?;
+
+  Ok(())
+}