Implement driver architecture with linker-section registration (AI)

- Created driver framework with probe/init lifecycle. Drivers register via
  REGISTER_DRIVER macro which places pointers in a .drivers linker section.
- During boot, init_drivers() iterates the section, probes each driver
  (checking if hardware is present), and initializes those that respond OK.
- Added .drivers section to linker.ld with __drivers_start/__drivers_end
  symbols for iteration.
- Also added .rodata.* pattern to the .rodata section for string literals
  placed in sub-sections by the compiler.
- No drivers are registered yet; the VGA driver will be the first.

Tested: boots cleanly with driver scan completing (0 registered, 0 loaded).

README.md

@@ -47,7 +47,7 @@ Once a task is completed, it should be checked off.
 - [x] Create a physical memory allocator and mapper. The kernel should live in the upper last gigabyte of virtual memory. It should support different zones (e.g.: `SUB_16M`, `DEFAULT`, ...) These zones describe the region of memory that memory should be allocated in. If it is not possible to allocate in that region (because it is full, or has 0 capacity to begin with), it should fallback to another zone.
 - [x] Create a paging subsystem. It should allow drivers to allocate and deallocate pages at will.
 - [x] Create a memory allocator. This should provide the kernel with `malloc` and `free`. Internally, it should use the paging subsystem to ensure that the address it returns have actual RAM paged to them.
-- [ ] Create an initial driver architecture, allowing different drivers included in the kernel to test whether they should load or not.
+- [x] Create an initial driver architecture, allowing different drivers included in the kernel to test whether they should load or not.
 - [ ] Create a VGA driver. On startup, some memory statistics should be displayed, as well as boot progress.
 - [ ] Create subsystem for loading new processes in Ring 3.
 - [ ] Update the build script to generate a ramdisk containing any applications to run. This initial ramdisk is in CPIO format.

src/CMakeLists.txt

@@ -11,6 +11,7 @@ add_executable(kernel
     paging.c
     kmalloc.c
     string.c
+    driver.c
     interrupts.S
     kernel.c
 )

src/driver.c

@@ -0,0 +1,72 @@
+/**
+ * @file driver.c
+ * @brief Driver framework implementation.
+ *
+ * Iterates over all driver descriptors placed in the .drivers linker section
+ * by the REGISTER_DRIVER macro. Each driver is probed and, if the probe
+ * succeeds, initialized.
+ */
+
+#include "driver.h"
+#include "port_io.h"
+#include <stddef.h>
+
+/* Debug print helpers defined in kernel.c */
+extern void offset_print(const char *str);
+extern void print_hex(uint32_t val);
+
+/**
+ * Linker-provided symbols marking the start and end of the .drivers section.
+ * Each entry is a pointer to a driver_t.
+ */
+extern const driver_t *__drivers_start[];
+extern const driver_t *__drivers_end[];
+
+void init_drivers(void) {
+    const driver_t **drv;
+    int loaded = 0;
+    int skipped = 0;
+    int failed = 0;
+
+    offset_print("  DRIVERS: scanning registered drivers...\n");
+
+    for (drv = __drivers_start; drv < __drivers_end; drv++) {
+        const driver_t *d = *drv;
+        if (!d || !d->name) {
+            continue;
+        }
+
+        offset_print("  DRIVERS: probing ");
+        offset_print(d->name);
+        offset_print("... ");
+
+        /* Run probe function if provided */
+        if (d->probe) {
+            driver_probe_result_t result = d->probe();
+            if (result == DRIVER_PROBE_NOT_FOUND) {
+                offset_print("not found\n");
+                skipped++;
+                continue;
+            } else if (result == DRIVER_PROBE_ERROR) {
+                offset_print("probe error\n");
+                failed++;
+                continue;
+            }
+        }
+
+        /* Run init function */
+        if (d->init) {
+            int ret = d->init();
+            if (ret != 0) {
+                offset_print("init failed\n");
+                failed++;
+                continue;
+            }
+        }
+
+        offset_print("loaded\n");
+        loaded++;
+    }
+
+    offset_print("  DRIVERS: done\n");
+}

src/driver.h

@@ -0,0 +1,56 @@
+/**
+ * @file driver.h
+ * @brief Kernel driver architecture.
+ *
+ * Provides a simple framework for registering and initializing kernel drivers.
+ * Each driver provides a probe function that returns whether it should load,
+ * and an init function that performs the actual initialization.
+ *
+ * Drivers are registered at compile time using the REGISTER_DRIVER macro,
+ * which places driver descriptors in a special linker section. The kernel
+ * iterates over all registered drivers during boot.
+ */
+
+#ifndef DRIVER_H
+#define DRIVER_H
+
+#include <stdint.h>
+
+/** Driver probe result codes. */
+typedef enum {
+    DRIVER_PROBE_OK = 0,        /**< Driver should be loaded. */
+    DRIVER_PROBE_NOT_FOUND = 1, /**< Hardware not found, skip this driver. */
+    DRIVER_PROBE_ERROR = 2      /**< Error during probing. */
+} driver_probe_result_t;
+
+/**
+ * Driver descriptor structure.
+ *
+ * Each driver provides a name, a probe function (to test if hardware is
+ * present), and an init function (to set up the driver).
+ */
+typedef struct driver {
+    const char *name;                     /**< Human-readable driver name. */
+    driver_probe_result_t (*probe)(void); /**< Probe function. Returns DRIVER_PROBE_OK if driver should load. */
+    int (*init)(void);                    /**< Init function. Returns 0 on success, non-zero on failure. */
+} driver_t;
+
+/**
+ * Register a driver.
+ *
+ * Places the driver descriptor in the .drivers linker section so it
+ * is automatically discovered during boot.
+ */
+#define REGISTER_DRIVER(drv) \
+    static const driver_t * __attribute__((used, section(".drivers"))) \
+    _driver_##drv = &(drv)
+
+/**
+ * Initialize all registered drivers.
+ *
+ * Iterates over the .drivers section, probes each driver, and initializes
+ * those that respond positively to probing.
+ */
+void init_drivers(void);
+
+#endif /* DRIVER_H */

src/kernel.c

@@ -8,6 +8,7 @@
 #include "pmm.h"
 #include "paging.h"
 #include "kmalloc.h"
+#include "driver.h"
 
 void offset_print(const char *str)
 {
@@ -67,6 +68,9 @@ void kernel_main(uint32_t magic, uint32_t addr) {
     init_kmalloc();
     offset_print("Memory allocator initialized\n");
 
+    init_drivers();
+    offset_print("Drivers initialized\n");
+
     /* Test kmalloc/kfree */
     uint32_t *test_alloc = (uint32_t *)kmalloc(64);
     if (test_alloc) {

src/linker.ld

@@ -15,6 +15,14 @@ SECTIONS
 	.rodata BLOCK(4K) : ALIGN(4K)
 	{
 		*(.rodata)
+		*(.rodata.*)
+	}
+
+	.drivers BLOCK(4K) : ALIGN(4K)
+	{
+		__drivers_start = .;
+		KEEP(*(.drivers))
+		__drivers_end = .;
 	}
 
 	.data BLOCK(4K) : ALIGN(4K)