kalloc.[ch] from xv6, memory.[ch] containing memory probing algorithm and constants

lib/memory.c

@@ -0,0 +1,29 @@
+#include <memory.h>
+#include <string.h>
+#include <uart.h>
+
+#define MAX_PROBE_SIZE (256 * 1024 * 1024) // Probe up to 256 MiB max
+#define PROBE_STEP     0x1000              // Probe every 4 KiB page
+
+size_t probe_memory(void) {
+    volatile u32 *addr;
+    u32           test_pattern = 0xA5A5A5A5;
+    size_t        detected = 0;
+
+    for (size_t offset = 4096 * 16; offset < MAX_PROBE_SIZE;
+         offset += PROBE_STEP) {
+        addr = (volatile u32 *)(KERNBASE + offset);
+
+        u32 old = *addr;
+        *addr = test_pattern;
+
+        if (*addr != test_pattern) {
+            break; // Memory not readable/writable here, stop probing
+        }
+
+        *addr = old; // restore original data
+        detected = offset + PROBE_STEP;
+    }
+
+    return detected;
+}

lib/memory.h

@@ -0,0 +1,16 @@
+#ifndef MEMORY_KERNEL_H
+#define MEMORY_KERNEL_H
+
+#include <types.h>
+
+/* These are hardcoded for now */
+#define KERNBASE 0x80000000L
+#define PHYSTOP  (KERNBASE + 128 * 1024 * 1024)
+
+/**
+ * Returns size in bytes of detected RAM In qemu, it requires a trap handler to
+ * handle the interrupt when accessing unavailable memory.
+ */
+size_t probe_memory(void);
+
+#endif