From 3b66779d9a8325c77c6cfbf1565885f98da5378f Mon Sep 17 00:00:00 2001
From: Danny Holman <dholman@gymli.org>
Date: Thu, 28 Mar 2024 21:55:33 -0500
Subject: arch: i386: kernel: implement a kmalloc function

Add a basic kmalloc implementation. This allows the kernel to allocate
blocks smaller than a whole page.

Signed-off-by: Danny Holman <dholman@gymli.org>
---
 arch/i386/kernel/kmalloc.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++
 arch/i386/make.config      |  1 +
 2 files changed, 67 insertions(+)
 create mode 100644 arch/i386/kernel/kmalloc.c

(limited to 'arch')

diff --git a/arch/i386/kernel/kmalloc.c b/arch/i386/kernel/kmalloc.c
new file mode 100644
index 0000000..183545a
--- /dev/null
+++ b/arch/i386/kernel/kmalloc.c
@@ -0,0 +1,66 @@
+#include <kernel/kmalloc.h>
+#include <kernel/paging.h>
+#include <kernel/pmem.h>
+#include <kernel/asm.h>
+#include <kernel/errno.h>
+#include <kernel/panic.h>
+#include <stdint.h>
+
+static uintptr_t heap_start = KEND + 0xC0001000;
+static uintptr_t heap_end = 0xFFFFF000;
+
+static void *kbrk = NULL;
+static struct mem_block *first = NULL;
+
+void _request_page(void) {
+        uintptr_t paddr = pfa_alloc();
+        if (paddr == PFA_ALLOC_ERR)
+                panic("Out of physical memory");
+
+        uintptr_t vaddr = PGROUNDDN((uintptr_t)kbrk + PAGE_SIZE);
+        kbrk += PAGE_SIZE;
+        map_page(NULL, paddr, vaddr, PD_PRES | PD_RW);
+}
+
+void kmalloc_init(void) {
+        kbrk = (void*)(heap_start & 0xFFFFF000);
+        _request_page();
+        first = (struct mem_block*)kbrk;
+        first->start = (uintptr_t)kbrk + sizeof(struct mem_block);
+        first->size = 0;
+        first->alloc = 1;
+        first->next = NULL;
+}
+
+void* kmalloc(size_t sz) {
+        if (kbrk == NULL)
+                panic("Attmpted to malloc before initialization");
+        if ((uintptr_t)kbrk >= heap_end)
+                return NULL;
+
+        struct mem_block *temp = first;
+        while (temp->next != NULL) {
+                if (temp->size <= sz && temp->alloc == 0)
+                        return (void*)temp->start;
+                temp = temp->next;
+        }
+
+        temp->next = (struct mem_block*)((uintptr_t)temp + sizeof(struct mem_block) + temp->size);
+        temp = temp->next;
+        temp->start = (uintptr_t)(temp + sizeof(struct mem_block));
+        temp->size = sz;
+        temp->alloc = 1;
+        temp->next = NULL;
+        return (void*)temp->start;
+}
+
+void kfree(void *ptr) {
+        struct mem_block *temp = first;
+        while (temp->next != NULL) {
+                if (temp->start == (uintptr_t)ptr) {
+                        temp->alloc = 0;
+                        return;
+                }
+        }
+        panic("Attempted to free memory not alloc'd");
+}
diff --git a/arch/i386/make.config b/arch/i386/make.config
index 1ffe8be..8499f1a 100644
--- a/arch/i386/make.config
+++ b/arch/i386/make.config
@@ -16,3 +16,4 @@ KERNEL_ARCH_OBJS=$(ARCHDIR)/boot/boot.o \
                  $(ARCHDIR)/kernel/syscall.o \
                  $(ARCHDIR)/kernel/paging.o \
                  $(ARCHDIR)/kernel/pmem.o \
+                 $(ARCHDIR)/kernel/kmalloc.o \
-- 
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