9 files changed, 1052 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..dd251ec
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,8 @@
+cmake_minimum_required(VERSION 3.0)
+
+set(CMAKE_C_STANDARD 11)
+set(CMAKE_C_STANDARD_REQUIRED On)
+set(CMAKE_C_EXTENSIONS Off)
+
+add_subdirectory(vm)
+add_subdirectory(vmrun)
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..4f259c4
--- /dev/null
+++ b/README.md
@@ -0,0 +1,14 @@
+# Lang Project
+
+## VM
+
+- Add support for type information in a separate stack.
+- Add understanding for record types so that we can view and debug rich types.
+- Add understanding of functions, or at least labels, so that we can hot-reload
+  them.
+
+## VM Runner
+
+- Text protocol over stdout -> websocketd -> web UI
+- Render stack view with type info, VM state view, etc.
+- Ability to step through code and view all information.
diff --git a/vm/CMakeLists.txt b/vm/CMakeLists.txt
new file mode 100644
index 0000000..3199ce6
--- /dev/null
+++ b/vm/CMakeLists.txt
@@ -0,0 +1,19 @@
+cmake_minimum_required(VERSION 3.0)
+
+project(vm)
+
+# Library
+add_library(vm
+  src/vm.c)
+
+target_include_directories(vm PUBLIC
+  ${CMAKE_CURRENT_SOURCE_DIR}/src)
+
+# Tests
+add_executable(vmtest
+  test/vm_test.c)
+
+target_link_libraries(vmtest
+  vm)
+
+target_compile_options(vmtest PRIVATE -DUNIT_TEST -Wall -Wextra)
diff --git a/vm/src/vm.c b/vm/src/vm.c
new file mode 100644
index 0000000..559ad5e
--- /dev/null
+++ b/vm/src/vm.c
@@ -0,0 +1,402 @@
+#include "vm.h"
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+// TODO: Make all these arguments of vm_new().
+
+// Program's main memory stack size.
+#define PROGRAM_STACK_SIZE (64 * 1024)
+
+// Locals stack size.
+#define LOCALS_STACK_SIZE 1024
+
+// Frame stack size.
+#define FRAME_STACK_SIZE (16 * 1024)
+
+// Block stack size.
+#define BLOCK_STACK_SIZE 1024
+
+#define IMPLICIT_LABEL -1
+
+// Locals index.
+typedef size_t Index;
+
+// Bools are internally I32s. 0 = false, non-zero = true.
+static Type     Bool = I32;
+typedef int32_t bool_t;
+
+/// Function frame.
+///
+/// Every Frame implicitly starts a Block. The function's locals are inside this
+/// implicit block.
+typedef struct Frame {
+  Label label;
+} Frame;
+
+/// A block of code, used for control flow.
+///
+/// Blocks have a label that the machine can jump to. Jumps are constrained to
+/// the block labels that are in scope.
+///
+/// Block termination automatically frees the block's locals.
+typedef struct Block {
+  Label  label;
+  size_t addr;         // Address (saved program counter) of the block.
+  size_t locals_start; // Offset into the locals stack.
+  size_t locals_size;  // Total size in bytes of local variables.
+} Block;
+
+typedef struct Vm {
+  struct {
+    bool exit : 1;
+  } flags;
+  int32_t  exit_code;
+  size_t   pc;     // Program instruction counter.
+  size_t   sp;     // Program stack pointer. Points to next available slot.
+  size_t   lsp;    // Locals stack pointer. Points to next available slot.
+  size_t   fsp;    // Frame stack pointer.
+  size_t   bsp;    // Block stack pointer. Points to current Block.
+  uint8_t* stack;  // Program stack. Program's main memory.
+  uint8_t* locals; // Locals stack. Stores locals for each Block.
+  Frame*   frames; // Frame stack for function calls.
+  Block*   blocks; // Block stack for control flow.
+} Vm;
+
+Vm* vm_new() {
+  Vm* vm = calloc(1, sizeof(Vm));
+  if (!vm) {
+    goto cleanup;
+  }
+  if (!(vm->stack = calloc(1, PROGRAM_STACK_SIZE))) {
+    goto cleanup;
+  }
+  if (!(vm->locals = calloc(1, LOCALS_STACK_SIZE))) {
+    goto cleanup;
+  }
+  if (!(vm->frames = calloc(FRAME_STACK_SIZE, sizeof(Frame)))) {
+    goto cleanup;
+  }
+  if (!(vm->blocks = calloc(BLOCK_STACK_SIZE, sizeof(Block)))) {
+    goto cleanup;
+  }
+  return vm;
+
+cleanup:
+  vm_del(&vm);
+  return 0;
+}
+
+void vm_del(Vm** pVm) {
+  if (pVm && *pVm) {
+    Vm* vm = *pVm;
+    if (vm->stack) {
+      free(vm->stack);
+    }
+    if (vm->locals) {
+      free(vm->locals);
+    }
+    if (vm->frames) {
+      free(vm->frames);
+    }
+    if (vm->blocks) {
+      free(vm->blocks);
+    }
+    free(vm);
+    *pVm = 0;
+  }
+}
+
+// static size_t get_size(Type type) {
+//   switch (type) {
+//   case I32:
+//     return sizeof(int32_t);
+//   }
+//   assert(false);
+//   return 0;
+// }
+
+// TODO: Not used?
+#define VM_ASSERT(expr) \
+  {}
+
+#define TOP(vm, type)              \
+  (assert(vm->sp >= sizeof(type)), \
+   *((const type*)&vm->stack[vm->sp - sizeof(type)]))
+
+#define PUSH(vm, value, type)                          \
+  assert(vm->sp + sizeof(type) <= PROGRAM_STACK_SIZE); \
+  *((type*)(&vm->stack[vm->sp])) = value;              \
+  vm->sp += sizeof(type);
+
+#define POP(vm, type)                                      \
+  (assert(vm->sp >= sizeof(type)), vm->sp -= sizeof(type), \
+   *((type*)(&vm->stack[vm->sp])))
+
+#define BLOCK_PUSH(vm, block)         \
+  assert(vm->bsp < BLOCK_STACK_SIZE); \
+  vm->blocks[++vm->bsp] = block;
+
+#define BLOCK_POP(vm)                            \
+  assert(vm->bsp > 0);                           \
+  vm->locals -= vm->blocks[vm->bsp].locals_size; \
+  vm->bsp--;
+
+#define PUSH_LOCAL(vm, type)                           \
+  assert(vm->lsp + sizeof(type) <= LOCALS_STACK_SIZE); \
+  /* Auto-initialize locals to 0. */                   \
+  *((type*)(&vm->locals[vm->lsp])) = 0;                \
+  vm->lsp += sizeof(type);                             \
+  vm->blocks[vm->bsp].locals_size += sizeof(type);
+
+#define POP_LOCAL(vm, type)                                  \
+  (assert(vm->lsp >= sizeof(type)), vm->lsp -= sizeof(type), \
+   vm->blocks[vm->bsp].locals -= sizeof(type),               \
+   *((type*)(&vm->locals[vm->lsp])))
+
+// TODO: Should be an offset from the current frame, not block.
+#define GET_LOCAL_PTR(vm, idx, type) \
+  ((const type*)(&vm->locals[vm->blocks[vm->bsp].locals_start + idx]))
+// TODO: Same here.
+#define GET_LOCAL_PTR_MUT(vm, idx, type) \
+  ((type*)(&vm->locals[vm->blocks[vm->bsp].locals_start + idx]))
+
+#define LOCAL_RD(vm, idx, type) (*GET_LOCAL_PTR(vm, idx, type))
+
+#define LOCAL_WR(vm, idx, val, type) (*GET_LOCAL_PTR_MUT(vm, idx, type) = val)
+
+static void push(Vm* vm, Inst inst) {
+  switch (inst.type) {
+  case I32:
+    PUSH(vm, inst.payload.i32, int32_t);
+    break;
+  case F32:
+    PUSH(vm, inst.payload.f32, float);
+    break;
+  }
+}
+
+static Value pop(Vm* vm, Type type) {
+  Value val;
+  switch (type) {
+  case I32:
+    val.i32 = POP(vm, int32_t);
+    break;
+  case F32:
+    val.f32 = POP(vm, float);
+    break;
+  }
+  return val;
+}
+
+static void vm_exit(Vm* vm, Inst inst) {
+  vm->exit_code  = vm->sp == 0 ? 0 : POP(vm, int32_t);
+  vm->flags.exit = true;
+}
+
+#define ADD(vm, a, b, field, type)         \
+  {                                        \
+    type result = ((a.field) + (b.field)); \
+    PUSH(vm, result, type);                \
+  }
+
+static void add(Vm* vm, Type type) {
+  Value opr1 = pop(vm, type);
+  Value opr2 = pop(vm, type);
+  switch (type) {
+  case I32:
+    ADD(vm, opr1, opr2, i32, int32_t);
+    break;
+
+  case F32:
+    ADD(vm, opr1, opr2, f32, float);
+    break;
+  }
+}
+
+static void dec(Vm* vm, Type type) {
+  Value top = pop(vm, type);
+  switch (type) {
+  case I32:
+    PUSH(vm, top.i32 - 1, int32_t);
+    break;
+  case F32:
+    PUSH(vm, top.f32 - 1.0f, float);
+    break;
+  }
+}
+
+static void empty(Vm* vm) { PUSH(vm, vm->sp == 0, bool_t); }
+
+#define CMP(vm, val, type) (POP(vm, type) == val)
+
+static void cmp(Vm* vm, Inst inst) {
+  switch (inst.type) {
+  case I32:
+    PUSH(vm, CMP(vm, inst.payload.i32, int32_t), bool_t);
+    break;
+  case F32:
+    PUSH(vm, CMP(vm, inst.payload.f32, float), bool_t);
+    break;
+  }
+}
+
+static void end(Vm* vm) { BLOCK_POP(vm); }
+
+static void loop(Vm* vm, Inst inst) {
+  const Block block = (Block){.label = inst.payload.i32, .addr = vm->pc};
+  BLOCK_PUSH(vm, block);
+}
+
+static void br(Vm* vm, Inst inst) {
+  const Branch  branch         = inst.payload.branch;
+  const int32_t label          = branch.label;
+  const bool    value          = branch.expected;
+  const bool    is_conditional = branch.conditional;
+  bool should_branch = is_conditional ? POP(vm, bool_t) == value : true;
+  // printf("is conditional: %d\n", is_conditional);
+  // printf("value: %d\n", value);
+  // printf("should branch: %d\n", should_branch);
+  if (should_branch) {
+    while (vm->bsp > 0) {
+      const Block block = vm->blocks[vm->bsp];
+      if (block.label == label) {
+        vm->pc = block.addr;
+        vm->pc--; // Account for increment at every step of the VM loop.
+        return;
+      }
+      vm->bsp--;
+    }
+    // We should be able to find the label in the block stack.
+    assert(false);
+  }
+}
+
+static void vm_break(Vm* vm, Inst inst) {
+  // TODO.
+  // Step over instructions until an End instruction is found.
+}
+
+static void local(Vm* vm, Type type) {
+  switch (type) {
+  case I32:
+    PUSH_LOCAL(vm, int32_t);
+    break;
+  case F32:
+    PUSH_LOCAL(vm, float);
+    break;
+  }
+}
+
+static void local_rd(Vm* vm, Inst inst) {
+  const Index idx = (Index)inst.payload.u64;
+  switch (inst.type) {
+  case I32:
+    PUSH(vm, LOCAL_RD(vm, idx, int32_t), int32_t);
+    break;
+  case F32:
+    PUSH(vm, LOCAL_RD(vm, idx, float), float);
+    break;
+  }
+}
+
+static void local_wr(Vm* vm, Inst inst) {
+  const Index idx = (Index)inst.payload.u64;
+  const Value top = pop(vm, inst.type);
+  switch (inst.type) {
+  case I32:
+    LOCAL_WR(vm, idx, top.i32, int32_t);
+    break;
+  case F32:
+    LOCAL_WR(vm, idx, top.f32, float);
+    break;
+  }
+}
+
+static void exec(Vm* vm, Inst inst) {
+  switch (inst.op) {
+  case Exit:
+    vm_exit(vm, inst);
+    break;
+  case Push:
+    push(vm, inst);
+    break;
+  case Pop:
+    pop(vm, inst.type);
+    break;
+  case Add:
+    add(vm, inst.type);
+    break;
+  case Sub:
+    break;
+  case Mul:
+    break;
+  case Div:
+    break;
+  case Dec:
+    dec(vm, inst.type);
+    break;
+  case Empty:
+    empty(vm);
+    break;
+  case Cmp:
+    cmp(vm, inst);
+    break;
+  case End:
+    end(vm);
+    break;
+  case Break:
+    vm_break(vm, inst);
+    break;
+  case Loop:
+    loop(vm, inst);
+    break;
+  case Br:
+    br(vm, inst);
+    break;
+  case Func: // TODO
+    break;
+  case Arg: // TODO
+    break;
+  case Call: // TODO
+    break;
+  case Local:
+    local(vm, inst.type);
+    break;
+  case LocalRd:
+    local_rd(vm, inst);
+    break;
+  case LocalWr:
+    local_wr(vm, inst);
+    break;
+  }
+}
+
+static void init(Vm* vm) {
+  // Create an implicit frame for the start of the program.
+  vm->frames[0] = (Frame){.label = IMPLICIT_LABEL};
+  vm->blocks[0] = (Block){.label = IMPLICIT_LABEL};
+  // TODO: Reset all Vm state.
+}
+
+int vm_run(Vm* vm, const Inst instructions[], size_t count) {
+  assert(vm);
+  init(vm);
+  for (vm->pc = 0; !vm->flags.exit && vm->pc < count; vm->pc++) {
+    const Inst inst = instructions[vm->pc];
+    exec(vm, inst);
+  }
+  // printf("exit code: %d\n", vm->exit_code);
+  return vm->exit_code;
+}
+
+void vm_print_stack(const Vm* vm) {
+  printf("stack start\n");
+  for (size_t i = 0; i < vm->sp; ++i) {
+    const char sep = (i == vm->sp - 1) ? '\n' : ' ';
+    printf("%x%c", vm->stack[i], sep);
+  }
+  printf("stack end\n");
+}
diff --git a/vm/src/vm.h b/vm/src/vm.h
new file mode 100644
index 0000000..03dfc88
--- /dev/null
+++ b/vm/src/vm.h
@@ -0,0 +1,166 @@
+#pragma once
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+typedef enum Op {
+  Exit, // Pop value from the stack and return as exit code. Return 0 if the
+        // stack is empty.
+  Push,
+  Pop,
+  Add,
+  Sub,
+  Mul,
+  Div,
+  Dec,   // Decrement the top of the stack by 1.
+  Empty, // Check whether the stack is empty. Pushes a bool.
+  Cmp,   // Pop the top of the stack and compare it with the payload. Pushes a
+         // bool.
+  /* Blocks */
+  End,   // Marks the end of a block.
+  Break, // Exit the current block.
+  Loop,  // Push a loop block. Payload (i32): label.
+  /* Branches */
+  Br, // Branch. Payload (i64): [(i32) conditional? | (i32) label].
+      // A condtional branch pops a bool from the stack and branches if true.
+      // The condition can also be negated. See br_if().
+  /* Functions */
+  Func,
+  Arg,
+  Call,
+  /* Locals */
+  Local,   // Create a local variable.
+  LocalRd, // Load a local variable into the top of the stack.
+  LocalWr, // Pop the top of the stack and store it in a local variable.
+} Op;
+
+typedef enum Type {
+  I32,
+  F32,
+} Type;
+
+// Label type for blocks and locals.
+typedef uint32_t Label;
+
+typedef struct Branch {
+  Label label;
+  bool  conditional : 1; // True for conditional branches.
+  bool  expected    : 1; // Comparison value for conditional branches.
+} Branch;
+
+typedef struct Function {
+  Label label;
+} Function;
+
+typedef struct Value {
+  union {
+    uint64_t u64;
+    int32_t  i32;
+    float    f32;
+    Branch   branch;
+    Label    label;
+  };
+} Value;
+
+typedef struct Inst {
+  Op    op   : 5;
+  Type  type : 2;
+  Value payload;
+} Inst;
+
+typedef struct Vm Vm;
+
+// -----------------------------------------------------------------------------
+// VM API
+
+/// Create a new virtual machine.
+Vm* vm_new();
+
+/// Destroy the virtual machine.
+void vm_del(Vm**);
+
+/// Execute code on the virtual machine.
+///
+/// Returns the program exit code if an exit operation is executed, 0 otherwise.
+int vm_run(Vm*, const Inst[], size_t count);
+
+/// Prints the virtual machine's stack to stdout.
+void vm_print_stack(const Vm*);
+
+// -----------------------------------------------------------------------------
+// Programming API
+
+/// Exit the program.
+static inline Inst vmExit() { return (Inst){.op = Exit}; }
+
+/// Push a value.
+static inline Inst vmPushI32(int32_t value) {
+  return (Inst){.op = Push, .type = I32, .payload = (Value){.i32 = value}};
+}
+
+/// Pop a value.
+static inline Inst vmPop(Type type) { return (Inst){.op = Pop, .type = type}; }
+
+/// Add two values.
+static inline Inst vmAdd(Type type) { return (Inst){.op = Add, .type = type}; }
+
+/// Decrement a value.
+static inline Inst vmDec(Type type) { return (Inst){.op = Dec, .type = type}; }
+
+/// Compare a value.
+static inline Inst vmCmpI32(int32_t value) {
+  return (Inst){.op = Cmp, .type = I32, .payload = (Value){.i32 = value}};
+}
+
+/// End the current block.
+static inline Inst vmEnd() { return (Inst){.op = End}; }
+
+/// Create a loop.
+static inline Inst vmLoop(Label label) {
+  return (Inst){.op = Loop, .payload = (Value){.label = label}};
+}
+
+/// Create the payload of a conditional branch.
+static inline Inst vmBr_if(bool value, Label label) {
+  return (Inst){
+      .op      = Br,
+      .payload = (Value){
+          .branch = {
+              .label       = label,
+              .conditional = 1,
+              .expected    = value,
+          }}};
+}
+
+/// Create a function.
+static inline Inst vmFunc(Label label) {
+  return (Inst){.op = Func, .payload = (Value){.label = label}};
+}
+
+/// Create a function argument.
+static inline Inst vmArg(Type type, Label label) {
+  return (Inst){.op = Arg, .type = type, .payload = (Value){.label = label}};
+}
+
+/// Call a function.
+static inline Inst vmCall(Label label) {
+  return (Inst){.op = Call, .payload = (Value){.label = label}};
+}
+
+/// Create a local variable.
+static inline Inst vmLocal(Type type, Label label) {
+  return (Inst){.op = Local, .type = type, .payload = (Value){.label = label}};
+}
+
+/// Read a local variable.
+static inline Inst vmLocalRd(Type type, Label label) {
+  return (Inst){
+      .op = LocalRd, .type = type, .payload = (Value){.label = label}};
+}
+
+/// Write a local variable.
+static inline Inst vmLocalWr(Type type, Label label) {
+  return (Inst){
+      .op = LocalWr, .type = type, .payload = (Value){.label = label}};
+}
diff --git a/vm/test/test.h b/vm/test/test.h
new file mode 100644
index 0000000..fd8dc22
--- /dev/null
+++ b/vm/test/test.h
@@ -0,0 +1,185 @@
+// SPDX-License-Identifier: MIT
+#pragma once
+
+#ifdef UNIT_TEST
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#if defined(__DragonFly__) || defined(__FreeBSD__) || defined(__FreeBSD_kernel__) ||     \
+    defined(__NetBSD__) || defined(__OpenBSD__)
+#define USE_SYSCTL_FOR_ARGS 1
+// clang-format off
+#include <sys/types.h>
+#include <sys/sysctl.h>
+// clang-format on
+#include <unistd.h>        // getpid
+#endif
+
+struct test_file_metadata;
+
+struct test_failure {
+        bool present;
+        const char *message;
+        const char *file;
+        int line;
+};
+
+struct test_case_metadata {
+        void (*fn)(struct test_case_metadata *, struct test_file_metadata *);
+        struct test_failure failure;
+        const char *name;
+        struct test_case_metadata *next;
+};
+
+struct test_file_metadata {
+        bool registered;
+        const char *name;
+        struct test_file_metadata *next;
+        struct test_case_metadata *tests;
+};
+
+struct test_file_metadata __attribute__((weak)) * test_file_head;
+
+#define SET_FAILURE(_message)                                                             \
+        metadata->failure = (struct test_failure) {                                       \
+                .message = _message, .file = __FILE__, .line = __LINE__, .present = true, \
+        }
+
+#define TEST_EQUAL(a, b)                                                                 \
+        do {                                                                             \
+                if ((a) != (b)) {                                                        \
+                        SET_FAILURE(#a " != " #b);                                       \
+                        return;                                                          \
+                }                                                                        \
+        } while (0)
+
+#define TEST_TRUE(a)                                                                     \
+        do {                                                                             \
+                if (!(a)) {                                                              \
+                        SET_FAILURE(#a " is not true");                                  \
+                        return;                                                          \
+                }                                                                        \
+        } while (0)
+
+#define TEST_STREQUAL(a, b)                                                              \
+        do {                                                                             \
+                if (strcmp(a, b) != 0) {                                                 \
+                        SET_FAILURE(#a " != " #b);                                       \
+                        return;                                                          \
+                }                                                                        \
+        } while (0)
+
+#define TEST_CASE(_name)                                                                  \
+        static void __test_h_##_name(struct test_case_metadata *,                         \
+                                     struct test_file_metadata *);                        \
+        static struct test_file_metadata __test_h_file;                                   \
+        static struct test_case_metadata __test_h_meta_##_name = {                        \
+            .name = #_name,                                                               \
+            .fn = __test_h_##_name,                                                       \
+        };                                                                                \
+        static void __attribute__((constructor(101))) __test_h_##_name##_register(void) { \
+                __test_h_meta_##_name.next = __test_h_file.tests;                         \
+                __test_h_file.tests = &__test_h_meta_##_name;                             \
+                if (!__test_h_file.registered) {                                          \
+                        __test_h_file.name = __FILE__;                                    \
+                        __test_h_file.next = test_file_head;                              \
+                        test_file_head = &__test_h_file;                                  \
+                        __test_h_file.registered = true;                                  \
+                }                                                                         \
+        }                                                                                 \
+        static void __test_h_##_name(                                                     \
+            struct test_case_metadata *metadata __attribute__((unused)),                  \
+            struct test_file_metadata *file_metadata __attribute__((unused)))
+
+extern void __attribute__((weak)) (*test_h_unittest_setup)(void);
+/// Run defined tests, return true if all tests succeeds
+/// @param[out] tests_run if not NULL, set to whether tests were run
+static inline void __attribute__((constructor(102))) run_tests(void) {
+        bool should_run = false;
+#ifdef USE_SYSCTL_FOR_ARGS
+        int mib[] = {
+                CTL_KERN,
+#if defined(__NetBSD__) || defined(__OpenBSD__)
+                KERN_PROC_ARGS,
+                getpid(),
+                KERN_PROC_ARGV,
+#else
+                KERN_PROC,
+                KERN_PROC_ARGS,
+                getpid(),
+#endif
+        };
+        char *arg = NULL;
+        size_t arglen;
+        sysctl(mib, sizeof(mib) / sizeof(mib[0]), NULL, &arglen, NULL, 0);
+        arg = malloc(arglen);
+        sysctl(mib, sizeof(mib) / sizeof(mib[0]), arg, &arglen, NULL, 0);
+#else
+        FILE *cmdlinef = fopen("/proc/self/cmdline", "r");
+        char *arg = NULL;
+        int arglen;
+        fscanf(cmdlinef, "%ms%n", &arg, &arglen);
+        fclose(cmdlinef);
+#endif
+        for (char *pos = arg; pos < arg + arglen; pos += strlen(pos) + 1) {
+                if (strcmp(pos, "--unittest") == 0) {
+                        should_run = true;
+                        break;
+                }
+        }
+        free(arg);
+
+        if (!should_run) {
+                return;
+        }
+
+        if (&test_h_unittest_setup) {
+                test_h_unittest_setup();
+        }
+
+        struct test_file_metadata *i = test_file_head;
+        int failed = 0, success = 0;
+        while (i) {
+                fprintf(stderr, "Running tests from %s:\n", i->name);
+                struct test_case_metadata *j = i->tests;
+                while (j) {
+                        fprintf(stderr, "\t%s ... ", j->name);
+                        j->failure.present = false;
+                        j->fn(j, i);
+                        if (j->failure.present) {
+                                fprintf(stderr, "failed (%s at %s:%d)\n", j->failure.message,
+                                        j->failure.file, j->failure.line);
+                                failed++;
+                        } else {
+                                fprintf(stderr, "passed\n");
+                                success++;
+                        }
+                        j = j->next;
+                }
+                fprintf(stderr, "\n");
+                i = i->next;
+        }
+        int total = failed + success;
+        fprintf(stderr, "Test results: passed %d/%d, failed %d/%d\n", success, total,
+                failed, total);
+        exit(failed == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
+}
+
+#else
+
+#include <stdbool.h>
+
+#define TEST_CASE(name) static void __attribute__((unused)) __test_h_##name(void)
+
+#define TEST_EQUAL(a, b)                                                                 \
+        (void)(a);                                                                       \
+        (void)(b)
+#define TEST_TRUE(a) (void)(a)
+#define TEST_STREQUAL(a, b)                                                              \
+        (void)(a);                                                                       \
+        (void)(b)
+
+#endif
diff --git a/vm/test/vm_test.c b/vm/test/vm_test.c
new file mode 100644
index 0000000..2d1a91f
--- /dev/null
+++ b/vm/test/vm_test.c
@@ -0,0 +1,182 @@
+#include "vm.h"
+
+#include "test.h"
+
+#include <stdio.h>
+
+/// Create and destroy a vm.
+TEST_CASE(vm_create_destroy) {
+  Vm* vm = vm_new();
+  TEST_TRUE(vm != 0);
+  vm_del(&vm);
+}
+
+// Exit with an implicit 0 exit code.
+TEST_CASE(vm_exit_implicit) {
+  // clang-format off
+  const Inst instructions[] = {
+    vmExit(),
+  };
+  // clang-format on
+
+  Vm* vm = vm_new();
+  TEST_TRUE(vm != 0);
+  const int exit_code =
+      vm_run(vm, instructions, sizeof(instructions) / sizeof(Inst));
+  TEST_TRUE(exit_code == 0);
+  vm_del(&vm);
+}
+
+// Exit with an explicit exit code.
+TEST_CASE(vm_exit_explicit) {
+  const int32_t expected = 17;
+
+  // clang-format off
+  const Inst instructions[] = {
+    vmPushI32(expected),
+    vmExit(),
+  };
+  // clang-format on
+
+  Vm* vm = vm_new();
+  TEST_TRUE(vm != 0);
+  const int exit_code =
+      vm_run(vm, instructions, sizeof(instructions) / sizeof(Inst));
+  TEST_TRUE(exit_code == expected);
+  vm_del(&vm);
+}
+
+/// Add two i32 numbers.
+TEST_CASE(vm_add_i32) {
+  const int n1 = 2;
+  const int n2 = 3;
+
+  // clang-format off
+  const Inst instructions[] = {
+      vmPushI32(n1),
+      vmPushI32(n2),
+      vmAdd(I32),
+      vmExit(),
+  };
+  // clang-format on
+
+  Vm* vm = vm_new();
+  TEST_TRUE(vm != 0);
+  const int exit_code =
+      vm_run(vm, instructions, sizeof(instructions) / sizeof(Inst));
+  TEST_EQUAL(exit_code, n1 + n2);
+  vm_del(&vm);
+}
+
+/// Sum an array of numbers with 4 add instructions.
+TEST_CASE(vm_sum_array_i32_explicit) {
+  const int vals[5] = {1, 2, 3, 4, 5};
+
+  // clang-format off
+  const Inst instructions[] = {
+      vmPushI32(vals[0]),
+      vmPushI32(vals[1]),
+      vmPushI32(vals[2]),
+      vmPushI32(vals[3]),
+      vmPushI32(vals[4]),
+      vmAdd(I32),
+      vmAdd(I32),
+      vmAdd(I32),
+      vmAdd(I32),
+      vmExit(),
+  };
+  // clang-format on
+
+  int sum = 0;
+  for (size_t i = 0; i < sizeof(vals) / sizeof(vals[0]); ++i) {
+    sum += vals[i];
+  }
+
+  Vm* vm = vm_new();
+  TEST_TRUE(vm != 0);
+  const int exit_code =
+      vm_run(vm, instructions, sizeof(instructions) / sizeof(Inst));
+  TEST_EQUAL(exit_code, sum);
+  vm_del(&vm);
+}
+
+/// Sum an array of numbers with a loop.
+TEST_CASE(vm_sum_array_i32_loop) {
+  const int vals[5] = {1, 2, 3, 4, 5};
+
+  const Label loop_label    = 0;
+  const Label counter_index = 0;
+
+  // clang-format off
+  const Inst instructions[] = {
+      vmPushI32(vals[0]),
+      vmPushI32(vals[1]),
+      vmPushI32(vals[2]),
+      vmPushI32(vals[3]),
+      vmPushI32(vals[4]),
+      vmLocal(I32, counter_index),
+      vmPushI32(sizeof(vals) / sizeof(vals[0]) - 1),
+      vmLocalWr(I32, counter_index),
+      vmLoop(loop_label),
+      vmAdd(I32),
+      vmLocalRd(I32, counter_index),
+      vmDec(I32),
+      // TODO: Could be useful to have a function that writes the local but
+      // leaves its value on the stack.
+      vmLocalWr(I32, counter_index),
+      vmLocalRd(I32, counter_index),
+      // TODO: Perhaps we should expect the comparison value to also be pushed
+      // to the stack.
+      vmCmpI32(0),
+      vmBr_if(false, loop_label),
+      vmEnd(),
+      vmExit(),
+  };
+  // clang-format on
+
+  int sum = 0;
+  for (size_t i = 0; i < sizeof(vals) / sizeof(vals[0]); ++i) {
+    sum += vals[i];
+  }
+
+  Vm* vm = vm_new();
+  TEST_TRUE(vm != 0);
+  const int exit_code =
+      vm_run(vm, instructions, sizeof(instructions) / sizeof(Inst));
+  TEST_EQUAL(exit_code, sum);
+  vm_del(&vm);
+}
+
+// Call a function to add two numbers.
+TEST_CASE(vm_function_call) {
+  const Label   func     = 0;
+  const Label   a        = 0;
+  const Label   b        = 1;
+  const int32_t a_val    = 3;
+  const int32_t b_val    = 5;
+  const int32_t expected = a + b;
+
+  // clang-format off
+  const Inst instructions[] = {
+    /* Function definition */
+    vmFunc(func),
+    vmArg(I32, b),
+    vmArg(I32, a),
+    vmAdd(I32),
+    vmEnd(),
+    /* Main program */
+    vmPushI32(a_val),
+    vmPushI32(b_val),
+    vmCall(func),
+    vmExit(),
+  };
+  // clang-format on
+
+  Vm* vm = vm_new();
+  TEST_TRUE(vm != 0);
+  // const int exit_code =
+  //     vm_run(vm, instructions, sizeof(instructions) / sizeof(Inst));
+  vm_del(&vm);
+}
+
+int main() { return 0; }
diff --git a/vmrun/CMakeLists.txt b/vmrun/CMakeLists.txt
new file mode 100644
index 0000000..1a81995
--- /dev/null
+++ b/vmrun/CMakeLists.txt
@@ -0,0 +1,11 @@
+cmake_minimum_required(VERSION 3.0)
+
+project(vmrun)
+
+add_executable(vmrun
+  src/main.c)
+
+target_link_libraries(vmrun
+  vm)
+
+target_compile_options(vmrun PRIVATE -Wall -Wextra)
diff --git a/vmrun/src/main.c b/vmrun/src/main.c
new file mode 100644
index 0000000..0bdd16f
--- /dev/null
+++ b/vmrun/src/main.c
@@ -0,0 +1,65 @@
+#include <vm.h>
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+
+typedef enum CommandType {
+  ExitSession,
+  PrintStack,
+} CommandType;
+
+typedef struct Command {
+  CommandType type;
+} Command;
+
+static bool read_command(char line[], Command* pCmd) {
+  static const char* delim = " \n";
+
+  const char* cmd = strtok(line, delim);
+  if (strcmp(cmd, "exit") == 0) {
+    *pCmd = (Command){.type = ExitSession};
+    return true;
+  } else if (strcmp(cmd, "print_stack") == 0) {
+    *pCmd = (Command){.type = PrintStack};
+    return true;
+  }
+  return false;
+}
+
+/// Runs a command.
+///
+/// Returns true unless on ExitSession.
+static bool run_command(Vm* vm, Command cmd) {
+  switch (cmd.type) {
+  case ExitSession:
+    return false;
+  case PrintStack:
+    vm_print_stack(vm);
+    break;
+  }
+  return true;
+}
+
+int main() {
+  Vm* vm = vm_new();
+  if (!vm) {
+    fprintf(stderr, "Failed to create VM\n");
+    return 1;
+  }
+
+  Command cmd;
+  bool    should_continue = true;
+  char    line[128];
+
+  while (should_continue && fgets(line, sizeof(line), stdin)) {
+    if (read_command(line, &cmd)) {
+      should_continue = run_command(vm, cmd);
+    } else {
+      fprintf(stderr, "Unknown command\n");
+    }
+  }
+
+  vm_del(&vm);
+  return 0;
+}