feat: expand user mode, add DOOM game, add manpages

programs/include/zenith/heap.h

@@ -0,0 +1,133 @@
+/*
+    * heap.h
+    * Userspace heap allocator for ZenithOS programs
+    * Free-list allocator backed by SYS_ALLOC page requests.
+    * Adapted from the kernel HeapAllocator.
+    * Copyright (c) 2025 Daniel Hammer
+*/
+
+#pragma once
+#include <zenith/syscall.h>
+
+namespace zenith {
+namespace heap_detail {
+
+    static constexpr uint64_t HEADER_MAGIC = 0x5A484541;  // "ZHEA"
+
+    struct Header {
+        uint64_t magic;
+        uint64_t size;     // user-requested size
+    } __attribute__((packed));
+
+    struct FreeNode {
+        uint64_t  size;    // total size of this free block (including node)
+        FreeNode* next;
+    };
+
+    // Per-process heap state (single TU per program, so static is fine)
+    static FreeNode  g_head{0, nullptr};
+    static bool      g_initialized = false;
+
+    static inline Header* get_header(void* block) {
+        return (Header*)((uint8_t*)block - sizeof(Header));
+    }
+
+    static inline void insert_free(void* ptr, uint64_t size) {
+        auto* node  = (FreeNode*)ptr;
+        node->size  = size;
+        node->next  = g_head.next;
+        g_head.next = node;
+    }
+
+    static inline void grow(uint64_t bytes) {
+        uint64_t pages = (bytes + 0xFFF) / 0x1000;
+        if (pages < 4) pages = 4;          // grow at least 16 KiB at a time
+
+        void* mem = zenith::alloc(pages * 0x1000);
+        if (mem != nullptr)
+            insert_free(mem, pages * 0x1000);
+    }
+
+} // namespace heap_detail
+
+    // ---- Public API ----
+
+    inline void* malloc(uint64_t size) {
+        using namespace heap_detail;
+
+        if (!g_initialized) {
+            grow(16 * 0x1000);             // seed with 64 KiB
+            g_initialized = true;
+        }
+
+        uint64_t needed = size + sizeof(Header);
+        needed = (needed + 15) & ~15ULL;   // 16-byte alignment
+
+        FreeNode* prev    = &g_head;
+        FreeNode* current = g_head.next;
+
+        while (current != nullptr) {
+            if (current->size >= needed) {
+                uint64_t blockSize = current->size;
+
+                // Unlink
+                prev->next = current->next;
+
+                // Split if worthwhile
+                if (blockSize > needed + sizeof(FreeNode) + 16) {
+                    void*    rest     = (void*)((uint8_t*)current + needed);
+                    uint64_t restSize = blockSize - needed;
+                    insert_free(rest, restSize);
+                }
+
+                // Write allocation header
+                Header* header = (Header*)current;
+                header->magic  = HEADER_MAGIC;
+                header->size   = size;
+
+                return (void*)((uint8_t*)header + sizeof(Header));
+            }
+
+            prev    = current;
+            current = current->next;
+        }
+
+        // No fit — grow and retry
+        grow(needed);
+        return malloc(size);
+    }
+
+    inline void mfree(void* ptr) {
+        using namespace heap_detail;
+
+        if (ptr == nullptr) return;
+
+        Header* header = get_header(ptr);
+
+        uint64_t blockSize = header->size + sizeof(Header);
+        blockSize = (blockSize + 15) & ~15ULL;
+
+        insert_free((void*)header, blockSize);
+    }
+
+    inline void* realloc(void* ptr, uint64_t size) {
+        if (ptr == nullptr) return malloc(size);
+
+        auto* header  = heap_detail::get_header(ptr);
+        uint64_t  old = header->size;
+
+        void* newBlock = malloc(size);
+        if (newBlock == nullptr) return nullptr;
+
+        // Copy the smaller of old/new sizes
+        uint64_t copySize = (old < size) ? old : size;
+        uint8_t* dst = (uint8_t*)newBlock;
+        uint8_t* src = (uint8_t*)ptr;
+        for (uint64_t i = 0; i < copySize; i++)
+            dst[i] = src[i];
+
+        mfree(ptr);
+        return newBlock;
+    }
+
+} // namespace zenith