From c36e1b5e5e069ce1735dcc2a94aa45ba72ea2441 Mon Sep 17 00:00:00 2001
From: Richard Qin <richard.qin.x@gmail.com>
Date: Tue, 9 Dec 2025 00:57:38 +0800
Subject: feat: Initial PMM implementation Introduce the foundational Physical
 Memory Manager (PMM) and restructure the project for modularity. Implemented
 basic PMM and related memory management headers (mm/pmm.h, mm/vm.h). Updated
 Makefile and build process to support new modular structure.

---
 src/kernel/mm/pmm.cc | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 src/kernel/mm/pmm.cc

(limited to 'src/kernel/mm/pmm.cc')

diff --git a/src/kernel/mm/pmm.cc b/src/kernel/mm/pmm.cc
new file mode 100644
index 0000000..9b68fcd
--- /dev/null
+++ b/src/kernel/mm/pmm.cc
@@ -0,0 +1,71 @@
+#include "kernel/pmm.h"
+#include "drivers/uart.h"
+
+extern "C" char kernel_end[];
+
+namespace PMM
+{
+    struct Run
+    {
+        struct Run *next;
+    };
+
+    struct
+    {
+        struct Run *freelist;
+    } kmem;
+
+    inline uint64_t PGROUNDUP(uint64_t a)
+    {
+        return (a + PGSIZE - 1) & ~(PGSIZE - 1);
+    }
+
+    void init()
+    {
+        uint64_t start = PGROUNDUP((uint64_t)kernel_end);
+
+        Drivers::uart_puts("PMM: Initializing from");
+
+        for (uint64_t p = start; p + PGSIZE <= PHYSTOP; p += PGSIZE)
+        {
+            free_page((void *)p);
+        }
+    }
+
+    void free_page(void* pa)
+    {
+        struct Run *r;
+        if (((uint64_t)pa % PGSIZE) != 0 || (uint64_t)pa < (uint64_t)kernel_end || (uint64_t)pa >= PHYSTOP)
+        {
+            Drivers::uart_puts("PMM: Error - Invalid free address\n");
+            return;
+        }
+        r = (struct Run*)pa;
+
+        r->next = kmem.freelist;
+        kmem.freelist = r;
+        
+    }
+
+    void* alloc_page()
+    {
+        struct Run* r;
+
+        r = kmem.freelist;
+        if (r)
+        {
+            kmem.freelist = r->next;
+
+            uint64_t *p = (uint64_t *)r;
+            for (int i = 0; i < PGSIZE / 8; i++)
+            {
+                p[i] = 0;
+            }
+        }
+        else
+        {
+            Drivers::uart_puts("PMM: Out of memory!\n");
+        }
+        return (void *)r;
+    }
+}
\ No newline at end of file
-- 
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