From e301006c1494674d94e1bcedcd3c3a638af7ec00 Mon Sep 17 00:00:00 2001
From: Danny Holman <dholman@gymli.org>
Date: Sun, 26 Nov 2023 18:49:11 -0600
Subject: arch: i386: alloc: add a physical memory manager

Add a simple, bitmap-based physical memory management system.

Signed-off-by: Danny Holman <dholman@gymli.org>
---
 arch/i386/include/kernel/alloc.h | 13 ++++++++++++
 arch/i386/kernel/alloc.c         | 43 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)
 create mode 100644 arch/i386/include/kernel/alloc.h
 create mode 100644 arch/i386/kernel/alloc.c

(limited to 'arch')

diff --git a/arch/i386/include/kernel/alloc.h b/arch/i386/include/kernel/alloc.h
new file mode 100644
index 0000000..986bcc5
--- /dev/null
+++ b/arch/i386/include/kernel/alloc.h
@@ -0,0 +1,13 @@
+#ifndef I386_ALLOC_H
+#define I386_ALLOC_H
+
+#include <kernel/multiboot.h>
+#include <stdint.h>
+#include <stddef.h>
+
+int alloc_init(struct mboot_info *info);
+void mark_bitmap(uint32_t paddr, int present);
+uint32_t pfa_alloc_frame(void);
+void pfa_free(uint32_t paddr, int num_frames);
+
+#endif
diff --git a/arch/i386/kernel/alloc.c b/arch/i386/kernel/alloc.c
new file mode 100644
index 0000000..d2ddf79
--- /dev/null
+++ b/arch/i386/kernel/alloc.c
@@ -0,0 +1,43 @@
+#include <kernel/alloc.h>
+#include <kernel/paging.h>
+#include <kernel/io.h>
+#include <stdint.h>
+
+extern uint32_t _bitmap_start;
+static uint32_t *bm_start = &_bitmap_start;
+
+static struct mboot_info *info;
+
+int alloc_init(struct mboot_info *info) {
+        struct mboot_mmap_entry *mme;
+        for (uint32_t i = 0; i < info->mmap_length; i += sizeof(struct mboot_mmap_entry)) {
+                mme = (struct mboot_mmap_entry*)(info->mmap_addr + i);
+                if (mme->type != MBOOT_MEM_AVAILABLE)
+                        mark_bitmap(mme->addr_low, 1);
+        }
+        return 0;
+}
+
+void mark_bitmap(uint32_t paddr, int present) {
+        uint32_t index = (paddr & 0xFFFFF000) / 4096 / 32;
+        uint32_t bit = (paddr & 0xFFFFF000) / 4096 % 32;
+        bm_start[index] |= (present << bit);
+}
+
+uint32_t pfa_alloc_frame(void) {
+        for (uint32_t i = 0; i < 4096; i++) {
+                uint32_t index = i / 32;
+                uint32_t bit = i % 32;
+                if ((bm_start[index] & (1 << bit)) == 0) {
+                        mark_bitmap(i*4096, 1);
+                        return i * 4096;
+                }
+        }
+        __asm__ volatile("hlt");
+        return 0xFFFFFFFF;
+}
+
+void pfa_free(uint32_t paddr, int num_frames) {
+        for (int i = 0; i < num_frames; i++)
+                mark_bitmap(paddr + (i*4096), 0);
+}
-- 
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