build: Track header dependencies, fix default goal, and repair the font table comment

Three build-correctness fixes plus README coverage of the new kernel core.

The Makefile had no header dependency tracking, so editing a header left every
unrebuilt caller linked against the old layout. That is how the desktop's
window paint callbacks silently landed at the wrong struct offset after
gui_window_t grew: gui_apps.o was never recompiled. Compiles now emit .d files
via -MMD -MP and the build pulls them in.

The include has to sit at the end of the file with .DEFAULT_GOAL pinned to
`all` -- a .d file's first rule would otherwise become make's default goal and
turn a bare `make` into a silent no-op.

drivers/video/canvas.c carried the same font table defect gui_gfx.c did: the
`// \` comment on the backslash glyph continues onto the next line, swallowing
the `]` entry and shifting every glyph from ']' onward by one, so all lowercase
text rendered one letter off.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01L5yKJT4Wo2cV3rfPrwY5MP

Makefile

@@ -283,7 +283,8 @@ ifeq ($(CONFIG_USERLAND_LAZYBOX), y)
     CONFIG_SRCS-y += userland/lazybox/lazybox.c userland/lazybox/shell.c userland/lazybox/sh.c userland/lazybox/nano.c userland/lazybox/snake.c userland/lazybox/tree.c userland/lazybox/coreutils.c
 endif
 
-CONFIG_SRCS-y += gui/gui.c gui/gui_gfx.c gui/gui_cursor.c gui/gui_wm.c gui/gui_desktop.c gui/gui_apps.c
+CONFIG_SRCS-y += gui/gui.c gui/gui_gfx.c gui/gui_cursor.c gui/gui_wm.c gui/gui_desktop.c gui/gui_apps.c \
+                 gui/gui_widgets.c gui/gui_icons.c gui/gui_dialog.c gui/gui_apps_ext.c
 
 # Deduplicate
 CONFIG_SRCS-y := $(sort $(CONFIG_SRCS-y))
@@ -312,6 +313,13 @@ else
     OTHER_OBJS = $(filter-out $(ENTRY_OBJ), $(S_OBJS) $(C_OBJS))
 endif
 
+# Generated dependency files, one per object. The include lives at the very
+# end of this file: a .d file's first rule would otherwise become make's
+# default goal and turn a bare `make` into a no-op.
+DEPS = $(C_OBJS:.o=.d) $(CPP_OBJS:.o=.d) $(S_OBJS:.o=.d)
+
+.DEFAULT_GOAL := all
+
 .PHONY: all clean run debug info configure menuconfig config tui nconfig defconfig x86_64_defconfig aarch64_defconfig armv8_defconfig armv8i_defconfig armv81_defconfig arm32_defconfig qemu help
 
 all: $(TARGET)
@@ -337,15 +345,19 @@ armv8_defconfig armv8i_defconfig armv81_defconfig arm32_defconfig:
 # -----------------------------------------------------------------------------
 # Compilation Rules
 # -----------------------------------------------------------------------------
+# Header dependency tracking: without this a header change leaves stale objects
+# behind, and a struct layout edit silently corrupts every unrebuilt caller.
+DEPFLAGS = -MMD -MP
+
 # C Source Files
 $(BUILD_DIR)/%.o: %.c include/config/autoconf.h
 	@mkdir -p $(dir $@)
-	$(CC) $(CFLAGS) -c $< -o $@
+	$(CC) $(CFLAGS) $(DEPFLAGS) -c $< -o $@
 
 # C++ Source Files
 $(BUILD_DIR)/%.o: %.cpp include/config/autoconf.h
 	@mkdir -p $(dir $@)
-	$(CXX) $(CXXFLAGS) -c $< -o $@
+	$(CXX) $(CXXFLAGS) $(DEPFLAGS) -c $< -o $@
 
 # x86_64 NASM Assembly Files
 $(BUILD_DIR)/%.o: %.asm
@@ -355,7 +367,7 @@ $(BUILD_DIR)/%.o: %.asm
 # ARM/AArch64 GNU Assembly Files (.S)
 $(BUILD_DIR)/%.o: %.S
 	@mkdir -p $(dir $@)
-	$(CC) $(CFLAGS) -c $< -o $@
+	$(CC) $(CFLAGS) $(DEPFLAGS) -c $< -o $@
 
 # Rust Source Compilation
 $(RUST_LIB): rust/src/lib.rs $(RUST_SRCS)
@@ -462,3 +474,5 @@ help:
 
 clean:
 	rm -rf $(BUILD_DIR) $(IMAGE)
+
+-include $(DEPS)

README.md

@@ -27,6 +27,20 @@
 
 ## 🌟 Key Architecture & Capabilities
 
+- 🧵 **Kernel Concurrency Core (`kernel/wait.c`, `kernel/futex.c`, `kernel/rcu.c`)**:
+  - **Wait Queues & Completions**: Sleeper parking with timed waits, one-shot completion barriers, and a static entry pool so a blocking path never re-enters the allocator (`waitinfo`).
+  - **Futex Hash Table**: 32 buckets with value re-check on the slow path, requeue support, and an `fmutex_t` sleeping mutex built on the uncontended-fastpath protocol (`futexinfo`).
+  - **Tiny RCU**: Lock-free readers with nesting depth tracking, deferred `call_rcu`/`kfree_rcu` callbacks, grace-period accounting, and `rcu_assign_pointer`/`rcu_dereference` publish barriers (`rcuinfo`).
+- 🧱 **Core Data Structures (`lib/rbtree.c`, `lib/kfifo.c`, `lib/hashtable.c`)**:
+  - **Red-Black Tree**: Linux-compatible parent-pointer rbtree with full insert/erase rebalancing, forward and reverse in-order iteration, and a black-height invariant validator.
+  - **kfifo Ring Buffer**: Power-of-two byte ring with free-running indices, so the wrap path costs one mask instead of a branch per byte.
+  - **Hash Table**: Separately-chained FNV-1a table with string or `u64` keys and rehash-on-growth at a 3/4 load factor.
+- 💾 **Block Page Cache (`mm/page_cache.c`)**:
+  - Write-back cache of 4 KB pages keyed by `(device, page index)`, indexed through the kernel hash table.
+  - CLOCK second-chance eviction with dirty write-back, pinning, per-device flush and invalidate, and live hit-rate telemetry (`pagecache`).
+- 🧪 **In-Kernel Test Harness (`kernel/ktest.c`)**:
+  - KUnit-style suites with assertion macros, per-case pass/fail reporting and timing.
+  - **6 built-in suites, 21 cases, 735 assertions** covering rbtree, kfifo, hashtable, RCU, futex, wait queues, page cache and libcore — runnable from the shell (`ktest`) or the desktop KTest Runner.
 - ⚡ **Freestanding C++17 OOP Kernel Engine (`kernel/cpp/`)**:
   - **Bare-Metal C++ Runtime**: `operator new`/`delete`, sized deallocation, placement `new`, pure virtual handlers (`__cxa_pure_virtual`), and `.init_array` global constructor dispatcher.
   - **Modern Generic Containers**: Pure freestanding `Vector<T>`, `UniquePtr<T>` (with polymorphic converting constructors and custom deleters), dynamic `String`, and move semantics (`kernel::move`, `kernel::forward`).
@@ -85,6 +99,8 @@
 - 🧰 **LazyBox Userland Suite (85+ Linux, Rust, C++ & SUB-Lang Applets)**:
   - Interactive shell with history, quote-aware tokenization, tab autocompletion, ANSI cursor editing, and script runner (`sh`).
   - GNU-compatible **Nano** visual text editor.
+  - **Text Processing Suite (`userland/lazybox/coreutils.c`)**: `sort`, `uniq`, `cut`, `tr`, `rev`, `tac`, `nl`, `seq`, `diff`, `xxd`, `du`, `factor`, `sum` and `truncate`, all reading through the VFS and handling the zero-length synthetic nodes procfs and sysfs expose.
+  - **Kernel Diagnostics**: `ktest`, `rcuinfo`, `futexinfo`, `waitinfo` and `pagecache`.
   - Full utilities: `ls`, `cat`, `touch`, `mkdir`, `rm`, `cp`, `pwd`, `cd`, `tree`, `find`, `wc`, `head`, `tail`, `stat`, `df`, `mkfs.vfat`, `hexdump`, `neofetch`, `uname`, `free`, `uptime`, `top`, `ps`, `pstree`, `kill`, `dmesg`, `netstat`, `ifconfig`, `ping`, `traceroute`, `curl`, `ssh`, `tts`, `alsamixer`, `sensors`, `rustinfo`, `chacha20`, `sha3sum`, `base64`, `cryptobench`, `fdisk`, `rfilter`, `dcache`, `watchdog`, `jsonquery`, `subinfo`, `subi`, `subpower`, `subbench`, `subquote`, `cppinfo`, `cpptest`, `snake`, and more.
 
 ---

drivers/video/canvas.c

@@ -70,7 +70,7 @@ static const uint8_t font8x8_basic[96][8] = {
     {0x66,0x66,0x66,0x3c,0x18,0x18,0x3c,0x00}, // Y
     {0xfe,0x06,0x0c,0x18,0x30,0x60,0xfe,0x00}, // Z
     {0x3c,0x30,0x30,0x30,0x30,0x30,0x3c,0x00}, // [
-    {0xc0,0x60,0x30,0x18,0x0c,0x06,0x02,0x00}, // \
+    {0xc0,0x60,0x30,0x18,0x0c,0x06,0x02,0x00}, // backslash
     {0x3c,0x0c,0x0c,0x0c,0x0c,0x0c,0x3c,0x00}, // ]
     {0x10,0x38,0x6c,0xc6,0x00,0x00,0x00,0x00}, // ^
     {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0xff}, // _