5 files changed, 775 insertions, 0 deletions

diff --git a/mem/CMakeLists.txt b/mem/CMakeLists.txt
new file mode 100644
index 0000000..233d2be
--- /dev/null
+++ b/mem/CMakeLists.txt
@@ -0,0 +1,26 @@
+cmake_minimum_required(VERSION 3.0)
+
+project(mem)
+
+# Library
+
+add_library(mem
+  src/mem.c)
+
+target_include_directories(mem PUBLIC
+  include)
+
+target_link_libraries(mem
+  list)
+
+target_compile_options(mem PRIVATE -Wall -Wextra)
+
+# Test
+
+add_executable(mem_test
+  test/mem_test.c)
+
+target_link_libraries(mem_test
+  mem)
+
+target_compile_options(mem_test PRIVATE -DUNIT_TEST -DNDEBUG -Wall -Wextra)
diff --git a/mem/include/mem.h b/mem/include/mem.h
new file mode 100644
index 0000000..30c24fc
--- /dev/null
+++ b/mem/include/mem.h
@@ -0,0 +1,149 @@
+/*
+ * Block-based Memory Allocator.
+ *
+ * Clients should use the macros to define and use allocators. They make the API
+ * type-safe.
+ *
+ * Like a pool/block-based allocator, this allocator stores data in fixed-size
+ * blocks. However, this allocator also supports allocation of contiguous chunks
+ * of a variable number of blocks.
+ *
+ * Chunk information is stored in a separate array so that client data is
+ * contiguous in the main pool of memory and better cached.
+ */
+#pragma once
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+/// Define a typed memory allocator backed by a statically-allocated array.
+#define DEF_MEM(MEM, TYPE, NUM_BLOCKS) \
+  typedef struct MEM {                 \
+    Memory mem;                        \
+    Chunk  chunks[NUM_BLOCKS];         \
+    TYPE   blocks[NUM_BLOCKS];         \
+  } MEM;
+
+/// Define a typed memory allocator backed by a dynamically-allocated array.
+#define DEF_MEM_DYN(MEM, TYPE) \
+  typedef struct MEM {         \
+    Memory mem;                \
+    Chunk* chunks;             \
+    TYPE*  blocks;             \
+  } MEM;
+
+/// Initialize a statically-backed memory allocator.
+#define mem_make(MEM)                                                       \
+  {                                                                         \
+    assert(MEM);                                                            \
+    const size_t block_size = sizeof((MEM)->blocks[0]);                     \
+    const size_t num_blocks = sizeof((MEM)->blocks) / block_size;           \
+    mem_make_(                                                              \
+        &(MEM)->mem, (MEM)->chunks, (MEM)->blocks, num_blocks, block_size); \
+  }
+
+/// Initialize a dynamically-backed memory allocator.
+#define mem_make_dyn(MEM, num_blocks, block_size) \
+  mem_make_(&(MEM)->mem, 0, 0, num_blocks, block_size)
+
+/// Destroy the allocator.
+///
+/// If the allocator is dynamically-backed, then this function frees the
+/// underlying memory.
+#define mem_del(MEM) mem_del_(&(MEM)->mem)
+
+/// Clear the allocator.
+///
+/// This function frees all of the allocator's blocks. The resulting allocator
+/// is as if it were newly created.
+#define mem_clear(MEM) mem_clear_(&(MEM)->mem)
+
+/// Allocate a new chunk of N blocks.
+/// Return a pointer to the first block of the chunk, or 0 if there is no memory
+/// left.
+/// New chunks are conveniently zeroed out.
+#define mem_alloc(MEM, num_blocks) mem_alloc_(&(MEM)->mem, num_blocks)
+
+/// Free the chunk.
+/// The chunk pointer is conveniently set to 0.
+#define mem_free(MEM, CHUNK) mem_free_(&(MEM)->mem, (void**)CHUNK)
+
+/// Return a pointer to a chunk given the chunk's handle.
+/// The chunk must have been allocated.
+#define mem_get_chunk(MEM, HANDLE) \
+  ((__typeof__((MEM)->blocks[0])*)mem_get_chunk_(&(MEM)->mem, HANDLE))
+
+/// Get the handle to the given chunk.
+#define mem_get_chunk_handle(MEM, CHUNK_PTR) \
+  mem_get_chunk_handle_(&(MEM)->mem, CHUNK_PTR)
+
+/// Iterate over the used chunks of the allocator.
+///
+/// The caller can use 'i' as the index of the current chunk.
+///
+/// It is valid to mem_free() the chunk at each step of the iteration.
+#define mem_foreach(MEM, ITER, BODY)                          \
+  size_t i = 0;                                               \
+  do {                                                        \
+    if ((MEM)->chunks[i].used) {                              \
+      __typeof__((MEM)->blocks[0])* ITER = &(MEM)->blocks[i]; \
+      (void)ITER;                                             \
+      BODY;                                                   \
+    }                                                         \
+    i = (MEM)->chunks[i].next;                                \
+  } while (i);
+
+// -----------------------------------------------------------------------------
+
+/// Chunk information.
+///
+/// Every chunk represents a contiguous array of some number of blocks. The
+/// allocator begins as one big unused chunk.
+///
+/// Allocation looks for a free chunk large enough to hold to requested number
+/// of blocks. If the free chunk is larger than the requested chunk size, then
+/// the requested chunk is carved out of the larger block.
+///
+/// Deallocation frees the chunk back and merges it with free neighbouring
+/// chunks. Two free chunks are never contiguous in memory.
+///
+/// 'next' and 'prev' always point to a valid chunk (e.g., 0). Allocation stops
+/// looking for free chunks when it loops over.
+typedef struct Chunk {
+  size_t num_blocks;
+  size_t prev;
+  size_t next;
+  bool   used;
+} Chunk;
+
+typedef struct Memory {
+  size_t   block_size_bytes;
+  size_t   num_blocks;
+  size_t   next_free_chunk;
+  bool     dynamic; /// True if blocks and chunks are dynamically-allocated.
+  Chunk*   chunks;  /// Array of chunk information.
+  uint8_t* blocks;  /// Array of blocks;
+} Memory;
+
+/// Create a memory allocator.
+///
+/// 'chunks' and 'blocks' may be user-provided (statically-backed allocator) or
+/// null (dynamically-backed allocator).
+/// - If null, the allocator malloc()s the memory for them.
+/// - If given:
+///   - `chunks` must be at least `num_blocks` chunks.
+///   - `blocks` must be at least `num_blocks` * `block_size_bytes` bytes.
+///
+/// All blocks are zeroed out for convenience.
+bool mem_make_(
+    Memory* mem, Chunk* chunks, void* blocks, size_t num_blocks,
+    size_t block_size_bytes);
+
+void   mem_del_(Memory*);
+void   mem_clear_(Memory*);
+void*  mem_alloc_(Memory*, size_t num_blocks);
+void   mem_free_(Memory*, void** chunk_ptr);
+void*  mem_get_chunk_(const Memory*, size_t chunk_handle);
+size_t mem_get_chunk_handle_(const Memory*, const void* chunk);
diff --git a/mem/src/mem.c b/mem/src/mem.c
new file mode 100644
index 0000000..ff97f0f
--- /dev/null
+++ b/mem/src/mem.c
@@ -0,0 +1,183 @@
+#include "mem.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+bool mem_make_(
+    Memory* mem, Chunk* chunks, void* blocks, size_t num_blocks,
+    size_t block_size_bytes) {
+  assert(mem);
+  assert((chunks && blocks) || (!chunks && !blocks));
+  assert(num_blocks >= 1);
+
+  mem->block_size_bytes = block_size_bytes;
+  mem->num_blocks       = num_blocks;
+  mem->next_free_chunk  = 0;
+
+  // Allocate chunks and blocks if necessary and zero them out.
+  if (!chunks) {
+    chunks       = calloc(num_blocks, sizeof(Chunk));
+    blocks       = calloc(num_blocks, block_size_bytes);
+    mem->dynamic = true;
+    if (!chunks || !blocks) {
+      return false;
+    }
+  } else {
+    memset(blocks, 0, num_blocks * block_size_bytes);
+    memset(chunks, 0, num_blocks * sizeof(Chunk));
+    mem->dynamic = false;
+  }
+  mem->chunks = chunks;
+  mem->blocks = blocks;
+
+  // Initialize the head as one large free chunk.
+  Chunk* head      = &mem->chunks[0];
+  head->num_blocks = num_blocks;
+
+  return true;
+}
+
+void mem_del_(Memory* mem) {
+  assert(mem);
+  if (mem->dynamic) {
+    if (mem->chunks) {
+      free(mem->chunks);
+      mem->chunks = 0;
+    }
+    if (mem->blocks) {
+      free(mem->blocks);
+      mem->blocks = 0;
+    }
+  }
+}
+
+void mem_clear_(Memory* mem) {
+  assert(mem);
+  mem->next_free_chunk = 0;
+  memset(mem->blocks, 0, mem->num_blocks * mem->block_size_bytes);
+  memset(mem->chunks, 0, mem->num_blocks * sizeof(Chunk));
+
+  // Initialize the head as one large free chunk.
+  Chunk* head      = &mem->chunks[0];
+  head->num_blocks = mem->num_blocks;
+}
+
+void* mem_alloc_(Memory* mem, size_t num_blocks) {
+  assert(mem);
+  assert(num_blocks >= 1);
+
+  // Search for the first free chunk that can accommodate num_blocks.
+  const size_t start     = mem->next_free_chunk;
+  size_t       chunk_idx = start;
+  bool         found     = false;
+  do {
+    Chunk* chunk = &mem->chunks[chunk_idx];
+    if (!chunk->used) {
+      if (chunk->num_blocks > num_blocks) {
+        // Carve out a smaller chunk when the found chunk is larger than
+        // requested.
+        // [prev] <--> [chunk] <--> [new next] <--> [next]
+        const size_t new_next_idx = chunk_idx + num_blocks;
+        Chunk*       new_next     = &mem->chunks[new_next_idx];
+        if (chunk->next) {
+          mem->chunks[chunk->next].prev = new_next_idx;
+        }
+        new_next->prev = chunk_idx;
+        new_next->next = chunk->next;
+        chunk->next    = new_next_idx;
+
+        new_next->num_blocks = chunk->num_blocks - num_blocks;
+        chunk->num_blocks    = num_blocks;
+
+        chunk->used = true;
+        found       = true;
+        break;
+      } else if (chunk->num_blocks == num_blocks) {
+        chunk->used = true;
+        found       = true;
+        break;
+      }
+    }
+    chunk_idx = chunk->next; // Last chunk points back to 0, which is always the
+                             // start of some chunk. 'next' and 'prev' are
+                             // always valid pointers.
+  } while (chunk_idx != start);
+
+  if (found) {
+    mem->next_free_chunk = mem->chunks[chunk_idx].next;
+    return &mem->blocks[chunk_idx * mem->block_size_bytes];
+  } else {
+    return 0; // Large-enough free chunk not found.
+  }
+}
+
+// The given pointer is a pointer to this first block of the chunk.
+void mem_free_(Memory* mem, void** chunk_ptr) {
+  assert(mem);
+  assert(chunk_ptr);
+
+  const size_t chunk_idx =
+      ((uint8_t*)*chunk_ptr - mem->blocks) / mem->block_size_bytes;
+  assert(chunk_idx < mem->num_blocks);
+  Chunk* chunk = &mem->chunks[chunk_idx];
+
+  // Disallow double-frees.
+  assert(chunk->used);
+
+  // Zero out the chunk so that we don't get stray values the next time it is
+  // allocated.
+  memset(&mem->blocks[chunk_idx], 0, chunk->num_blocks * mem->block_size_bytes);
+
+  // Free the chunk. If it is contiguous with other free chunks, then merge.
+  // We only need to look at the chunk's immediate neighbours because no two
+  // free chunks are left contiguous after merging.
+  chunk->used = false;
+  if (chunk->next) {
+    Chunk* next = &mem->chunks[chunk->next];
+    if (!next->used) {
+      // Pre:  [chunk] <--> [next] <--> [next next]
+      // Post: [  chunk + next   ] <--> [next next]
+      chunk->num_blocks += mem->chunks[chunk->next].num_blocks;
+      chunk->next = next->next;
+      if (next->next) {
+        Chunk* next_next = &mem->chunks[next->next];
+        next_next->prev  = chunk_idx;
+      }
+      next->prev = next->next = next->num_blocks = 0;
+    }
+  }
+  if (chunk->prev) {
+    Chunk* prev = &mem->chunks[chunk->prev];
+    if (!prev->used) {
+      // Pre:  [prev] <--> [chunk] <--> [next]
+      // Post: [  prev + chunk   ] <--> [next]
+      prev->num_blocks += chunk->num_blocks;
+      prev->next = chunk->next;
+      if (chunk->next) {
+        Chunk* next = &mem->chunks[chunk->next];
+        next->prev  = chunk->prev;
+      }
+      chunk->prev = chunk->next = chunk->num_blocks = 0;
+    }
+  }
+
+  *chunk_ptr = 0;
+}
+
+// The handle is the chunk's index. We don't call it an index in the public API
+// because from the user's perspective, two chunks allocated back-to-back need
+// not be +1 away (the offset depends on how large the first chunk is).
+void* mem_get_chunk_(const Memory* mem, size_t chunk_handle) {
+  assert(mem);
+  assert(chunk_handle < mem->num_blocks);
+  assert(mem->chunks[chunk_handle].used);
+  return &mem->blocks[chunk_handle * mem->block_size_bytes];
+}
+
+// The given chunk pointer is a pointer to the blocks array.
+size_t mem_get_chunk_handle_(const Memory* mem, const void* chunk) {
+  assert(mem);
+  const size_t block_byte_index = (const uint8_t*)chunk - mem->blocks;
+  assert(block_byte_index % mem->block_size_bytes == 0);
+  return block_byte_index / mem->block_size_bytes;
+}
diff --git a/mem/test/mem_test.c b/mem/test/mem_test.c
new file mode 100644
index 0000000..6ab4c7c
--- /dev/null
+++ b/mem/test/mem_test.c
@@ -0,0 +1,232 @@
+#include "mem.h"
+
+#include "test.h"
+
+#define NUM_BLOCKS 10
+
+DEF_MEM(test_mem, int, NUM_BLOCKS);
+
+static int count(test_mem* mem) {
+  int count = 0;
+  mem_foreach(mem, n, { count++; });
+  return count;
+}
+
+static int sum(test_mem* mem) {
+  int sum = 0;
+  mem_foreach(mem, n, { sum += *n; });
+  return sum;
+}
+
+// Create a statically-backed allocator.
+TEST_CASE(mem_create) {
+  test_mem mem;
+  mem_make(&mem);
+}
+
+// Create a dynamically-backed allocator.
+TEST_CASE(mem_create_dyn) {
+  DEF_MEM_DYN(dyn_mem, int);
+  
+  dyn_mem mem;
+  mem_make_dyn(&mem, NUM_BLOCKS, sizeof(int));
+}
+
+// Allocate N chunks of 1 block each.
+TEST_CASE(mem_fully_allocate) {
+  test_mem mem;
+  mem_make(&mem);
+
+  for (int i = 0; i < NUM_BLOCKS; ++i) {
+    const int* block = mem_alloc(&mem, 1);
+    TEST_TRUE(block != 0);
+  }
+}
+
+// Allocate N chunks of 1 block each, then free them.
+TEST_CASE(mem_fill_then_free) {
+  test_mem mem;
+  mem_make(&mem);
+
+  int* blocks[NUM_BLOCKS] = {0};
+  for (int i = 0; i < NUM_BLOCKS; i++) {
+    blocks[i] = mem_alloc(&mem, 1);
+    TEST_TRUE(blocks[i] != 0);
+  }
+
+  for (int i = 0; i < NUM_BLOCKS; i++) {
+    mem_free(&mem, &blocks[i]);
+    TEST_EQUAL(blocks[i], 0); // Pointer should be set to 0 on free.
+  }
+
+  TEST_EQUAL(count(&mem), 0);
+}
+
+// Attempt to allocate blocks past the maximum allocator size.
+// The allocator should handle the failed allocations gracefully.
+TEST_CASE(mem_allocate_beyond_max_size) {
+  test_mem mem;
+  mem_make(&mem);
+
+  // Fully allocate the mem.
+  for (int i = 0; i < NUM_BLOCKS; ++i) {
+    TEST_TRUE(mem_alloc(&mem, 1) != 0);
+  }
+
+  // Past the end.
+  for (int i = 0; i < NUM_BLOCKS; ++i) {
+    TEST_EQUAL(mem_alloc(&mem, 1), 0);
+  }
+}
+
+// Free blocks should always remain zeroed out.
+// This tests the invariant right after creating the allocator.
+TEST_CASE(mem_zero_free_blocks_after_creation) {
+  test_mem mem;
+  mem_make(&mem);
+
+  const int zero = 0;
+  for (int i = 0; i < NUM_BLOCKS; ++i) {
+    const int* block = (const int*)(mem.blocks) + i;
+    TEST_EQUAL(memcmp(block, &zero, sizeof(int)), 0);
+  }
+}
+
+// Free blocks should always remain zeroed out.
+// This tests the invariant after freeing a block.
+TEST_CASE(mem_zero_free_block_after_free) {
+  test_mem mem;
+  mem_make(&mem);
+
+  int* val = mem_alloc(&mem, 1);
+  TEST_TRUE(val != 0);
+  *val = 177;
+
+  int* old_val = val;
+  mem_free(&mem, &val);    // val pointer is set to 0.
+  TEST_EQUAL(*old_val, 0); // Block is zeroed out after free.
+}
+
+// Traverse an empty allocator.
+TEST_CASE(mem_traverse_empty) {
+  test_mem mem;
+  mem_make(&mem);
+
+  TEST_EQUAL(count(&mem), 0);
+}
+
+// Traverse a partially full allocator.
+TEST_CASE(mem_traverse_partially_full) {
+  const int N = NUM_BLOCKS / 2;
+
+  test_mem mem;
+  mem_make(&mem);
+
+  for (int i = 0; i < N; ++i) {
+    int* val = mem_alloc(&mem, 1);
+    TEST_TRUE(val != 0);
+    *val = i + 1;
+  }
+
+  TEST_EQUAL(sum(&mem), (N) * (N + 1) / 2);
+}
+
+// Traverse a full allocator.
+TEST_CASE(mem_traverse_full) {
+  test_mem mem;
+  mem_make(&mem);
+
+  for (int i = 0; i < NUM_BLOCKS; ++i) {
+    int* val = mem_alloc(&mem, 1);
+    TEST_TRUE(val != 0);
+    *val = i + 1;
+  }
+
+  TEST_EQUAL(sum(&mem), (NUM_BLOCKS) * (NUM_BLOCKS + 1) / 2);
+}
+
+// Get the ith (allocated) chunk.
+TEST_CASE(mem_get_block) {
+  test_mem mem;
+  mem_make(&mem);
+
+  for (int i = 0; i < NUM_BLOCKS; ++i) {
+    int* block = mem_alloc(&mem, 1);
+    TEST_TRUE(block != 0);
+    *block = i;
+    TEST_EQUAL(mem_get_chunk_handle(&mem, block), (size_t)i);
+  }
+
+  for (int i = 0; i < NUM_BLOCKS; ++i) {
+    TEST_EQUAL(*mem_get_chunk(&mem, i), i);
+  }
+}
+
+// Test merging.
+// 1. Allocate chunks of variable sizes.
+// 2. Free them in a different order.
+// 3. Then we should be able to allocate 1 chunk of N blocks.
+TEST_CASE(mem_fragmentation) {
+  test_mem mem;
+  mem_make(&mem);
+
+  int* blocks[NUM_BLOCKS] = {0};
+  int  next_block         = 0;
+
+#define ALLOC(num_blocks)                           \
+  blocks[next_block] = mem_alloc(&mem, num_blocks); \
+  TEST_TRUE(blocks[next_block] != 0);               \
+  next_block++;
+
+#define FREE(block_idx) mem_free(&mem, &blocks[block_idx])
+
+  // 5 total allocations of variable chunk sizes.
+  ALLOC(2); // 2;  idx = 0
+  ALLOC(3); // 5;  idx = 1
+  ALLOC(1); // 6;  idx = 2
+  ALLOC(3); // 9;  idx = 3
+  ALLOC(1); // 10; idx = 4
+
+  // Free the 5 allocations in a different order.
+  FREE(1);
+  FREE(3);
+  FREE(4);
+  FREE(2);
+  FREE(0);
+
+  // Should be able to allocate 1 chunk of N blocks.
+  const void* chunk = mem_alloc(&mem, NUM_BLOCKS);
+  TEST_TRUE(chunk != 0);
+}
+
+// Clear and re-use an allocator.
+TEST_CASE(mem_clear_then_reuse) {
+  test_mem mem;
+  mem_make(&mem);
+
+  // Allocate chunks, contents not important.
+  for (int i = 0; i < NUM_BLOCKS; ++i) {
+    int* chunk = mem_alloc(&mem, 1);
+    TEST_TRUE(chunk != 0);
+  }
+
+  mem_clear(&mem);
+
+  // Allocate chunks and assign values 0..N.
+  for (int i = 0; i < NUM_BLOCKS; ++i) {
+    int* chunk = mem_alloc(&mem, 1);
+    TEST_TRUE(chunk != 0);
+    *chunk = i + 1;
+  }
+
+  TEST_EQUAL(sum(&mem), NUM_BLOCKS * (NUM_BLOCKS + 1) / 2);
+}
+
+// Stress test.
+//
+// 1. Allocate the mem, either fully or partially. If fully, attempt to
+//    allocate some items past the end.
+//
+// 2. Free all allocated items in some random order.
+
+int main() { return 0; }
diff --git a/mem/test/test.h b/mem/test/test.h
new file mode 100644
index 0000000..fd8dc22
--- /dev/null
+++ b/mem/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