Remove original kalloc free-list memory allocator entirely for now

Makefile

@@ -55,7 +55,6 @@ quickstart:
 KERNEL_OBJ := \
 	kern/entry.o \
 	kern/start.o \
-	kern/kalloc.o \
 	kern/libkern/string.o \
 	kern/libkern/proc.o \
 	kern/libkern/uart.o \
@@ -64,6 +63,7 @@ KERNEL_OBJ := \
 	kern/libkern/spinlock.o \
 	kern/libkern/mini-printf.o \
 	kern/libkern/stdio.o \
+	kern/libkern/buddy.o \
 	kern/libkern/badrand.o
 
 kern/kernel.elf: $(KERNEL_OBJ)

kern/kalloc.c

@@ -1,77 +0,0 @@
-#include <kalloc.h>
-#include <memory.h>
-#include <panic.h>
-#include <riscv.h>
-#include <spinlock.h>
-#include <stdint.h>
-#include <string.h>
-
-// Physical memory allocator, for user processes,
-// kernel stacks, page-table pages,
-// and pipe buffers. Allocates whole 4096-byte pages.
-
-/** Free list of physical pages. */
-void freerange(void *physaddr_start, void *physaddr_end);
-
-/** First address after kernel. Provided kernel.ld */
-extern char kernel_end[];
-
-/** A run is a node in the free list. */
-struct Run {
-    struct Run *next;
-};
-
-/** Kernel memory allocator. */
-struct {
-    spinlock_t  lock;
-    struct Run *freelist;
-} kmem;
-
-void kalloc_init() {
-    spinlock_init(&kmem.lock);
-    freerange(kernel_end, (void *)PHYSTOP);
-}
-
-void freerange(void *physaddr_start, void *physaddr_end) {
-    char *p;
-    p = (char *)PGROUNDUP((u64)physaddr_start);
-    for (; p + PGSIZE <= (char *)physaddr_end; p += PGSIZE) kfree(p);
-}
-
-void kfree(void *pa) {
-    struct Run *r;
-
-    // Assert that page is a ligned to a page boundary and that its correctly
-    // sized
-    if (((u64)pa % PGSIZE) != 0 || (char *)pa < kernel_end || (u64)pa >= PHYSTOP)
-        PANIC("kfree");
-
-    // TODO: Kconfig this
-    // Fill with junk to catch dangling refs.
-    memset(pa, 1, PGSIZE);
-
-    r = (struct Run *)pa;
-
-    spin_lock(&kmem.lock);
-    r->next = kmem.freelist;
-    kmem.freelist = r;
-    spin_unlock(&kmem.lock);
-}
-
-void *kalloc(void) {
-    struct Run *r;
-
-    spin_lock(&kmem.lock);
-
-    r = kmem.freelist;
-
-    if (r)
-        kmem.freelist = r->next;
-
-    spin_unlock(&kmem.lock);
-
-    if (r)
-        memset((char *)r, 5, PGSIZE); // fill with junk
-
-    return (void *)r;
-}

kern/kalloc.h

@@ -1,33 +0,0 @@
-#ifndef KALLOC_KERNEL_H
-#define KALLOC_KERNEL_H
-
-/**
- * Kernel memory allocator
- *
- * Allocate one 4096-byte page of physical memory.
- * Returns a pointer that the kernel can use.
- * Returns 0 if the memory cannot be allocated.
- * See: kalloc.c
- */
-void *kalloc(void);
-
-/**
- * Kernel memory allocator
- *
- * Free the page of physical memory pointed at by pa,
- * which normally should have been returned by a
- * call to kalloc().  (The exception is when
- * initializing the allocator; see kinit above.)
- * See: kalloc.c
- */
-void kfree(void *);
-
-/**
- * Initialize kernel memory allocator
- *
- * Called by main() on the way to the kernel's main loop.
- * See: kalloc.c
- */
-void kalloc_init(void);
-
-#endif // KALLOC_KERNEL_H

kern/kernel.ld

@@ -1,14 +1,13 @@
 OUTPUT_ARCH( "riscv" )
 ENTRY( _entry ) /* See: entry.S */
 
+MEMORY
+{
+  RAM (rwx) : ORIGIN = 0x80000000, LENGTH = 128M
+}
+
 SECTIONS
 {
-  /*
-   * ensure that entry.S / _entry is at 0x80000000,
-   * where qemu's -kernel jumps.
-   */
-  . = 0x80000000;
-
   /*
    * This section contains the code. This is, the machine language instructions
    * that will be executed by the processor. In here we will find symbols
@@ -35,7 +34,7 @@ SECTIONS
 
     /* Define symbol etext to be the current location. */
     PROVIDE(etext = .);
-  } :text
+  } > RAM :text
 
   /*
    * This contains any data that is marked as read only.
@@ -47,7 +46,7 @@ SECTIONS
     *(.srodata*) /* do not need to distinguish this from .rodata */
     . = ALIGN(16);
     *(.rodata*)
-  }
+  } > RAM
 
   /*
    * This section contains initialized global and static variables.
@@ -58,7 +57,7 @@ SECTIONS
     *(.sdata*) /* do not need to distinguish this from .data */
     . = ALIGN(16);
     *(.data*)
-  }
+  } > RAM
 
   /*
    * Contains all uninitialized global and static var iables. These are usually
@@ -71,10 +70,12 @@ SECTIONS
     *(.sbss*) /* do not need to distinguish this from .bss */
     . = ALIGN(16);
     *(.bss*)
-  }
+  } > RAM
 
   /* Define symbol end as current location, note that this is not aligned, see vm.c */
   PROVIDE(kernel_end = .);
+  PROVIDE(__heap_start = ALIGN(32));
+  PROVIDE(__heap_end = ORIGIN(RAM) + LENGTH(RAM));
 }
 
 PHDRS {

kern/libkern/assert.h

@@ -1,4 +1,5 @@
 #include <panic.h>
+#include <stdio.h>
 
 #define assert(cond)                                                                                                   \
     do {                                                                                                               \

kern/libkern/buddy.c

@@ -0,0 +1,139 @@
+#include <assert.h>
+#include <buddy.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+
+#define MAX_ORDER      22 // 2^22 * min_block_size = max allocatable block
+#define MIN_BLOCK_SIZE 32 // Smallest allocatable block
+
+typedef struct free_block {
+    struct free_block *next;
+} free_block_t;
+
+typedef struct {
+    uint8_t order;
+} block_header_t;
+
+static free_block_t *free_lists[MAX_ORDER + 1];
+
+uintptr_t heap_start = (uintptr_t)&__heap_start;
+uintptr_t heap_end = (uintptr_t)&__heap_end;
+
+// Utility: round up to next power of two
+static size_t next_pow2(size_t x) {
+    if (x <= 1)
+        return 1;
+    x--;
+    x |= x >> 1;
+    x |= x >> 2;
+    x |= x >> 4;
+    x |= x >> 8;
+    x |= x >> 16;
+#if UINTPTR_MAX > 0xffffffff
+    x |= x >> 32;
+#endif
+    return x + 1;
+}
+
+// Find order for size
+static int size_to_order(size_t size) {
+    size_t needed = (size < MIN_BLOCK_SIZE) ? MIN_BLOCK_SIZE : size;
+    size_t block_size = next_pow2(needed);
+    int    order = 0;
+    while ((MIN_BLOCK_SIZE << order) < block_size) {
+        order++;
+    }
+    return order;
+}
+
+// Initialize allocator
+void buddy_init(uintptr_t start, uintptr_t end) {
+    heap_start = (start + MIN_BLOCK_SIZE - 1) & ~(MIN_BLOCK_SIZE - 1);
+    heap_end = end & ~(MIN_BLOCK_SIZE - 1);
+
+    // Clear free lists
+    for (int i = 0; i <= MAX_ORDER; i++) free_lists[i] = NULL;
+
+    // Put the whole region as one big block
+    size_t total_size = heap_end - heap_start;
+    int    order = MAX_ORDER;
+    while ((MIN_BLOCK_SIZE << order) > total_size && order > 0) order--;
+
+    free_block_t *block = (free_block_t *)heap_start;
+    block->next = NULL;
+    free_lists[order] = block;
+}
+
+// Allocate memory
+void *buddy_alloc(size_t size) {
+    int order = size_to_order(size);
+
+    for (int i = order; i <= MAX_ORDER; i++) {
+        if (free_lists[i]) {
+            // Remove block from this list
+            free_block_t *block = free_lists[i];
+            free_lists[i] = block->next;
+
+            // Split down to requested order
+            while (i > order) {
+                i--;
+                uintptr_t     buddy_addr = (uintptr_t)block + (MIN_BLOCK_SIZE << i);
+                free_block_t *buddy = (free_block_t *)buddy_addr;
+                buddy->next = free_lists[i];
+                free_lists[i] = buddy;
+            }
+
+            /*
+             * Here, we install a header into the block. This will allow us to use free, without
+             * specifying size, since it can read the order from one byte before the block start.
+             */
+            {
+                block_header_t *hdr = (block_header_t *)block;
+                hdr->order = order;
+                return (void *)(hdr + 1); // return pointer after header
+                // return (void *)block; // Regular block return for reference
+            }
+        }
+    }
+    return NULL; // Out of memory
+}
+
+// Free memory
+int buddy_free(void *ptr) {
+    block_header_t *hdr = (block_header_t *)ptr - 1;
+    int             order = hdr->order;
+
+    assert_msg(order != MAX_ORDER, "The buddy freelist header seems to have been corrupted.");
+
+    uintptr_t addr = (uintptr_t)ptr;
+
+    while (order < MAX_ORDER) {
+        uintptr_t buddy_addr = addr ^ (MIN_BLOCK_SIZE << order);
+
+        // Check if buddy is in free list
+        free_block_t **prev = &free_lists[order];
+        free_block_t  *cur = free_lists[order];
+        while (cur) {
+            if ((uintptr_t)cur == buddy_addr) {
+                // Remove buddy from list
+                *prev = cur->next;
+                // Merge
+                if (buddy_addr < addr)
+                    addr = buddy_addr;
+                order++;
+                goto try_merge;
+            }
+            prev = &cur->next;
+            cur = cur->next;
+        }
+        break; // Buddy not free, stop
+    try_merge:;
+    }
+
+    free_block_t *block = (free_block_t *)addr;
+    block->next = free_lists[order];
+    free_lists[order] = block;
+
+    return order;
+}

kern/libkern/buddy.h

@@ -0,0 +1,22 @@
+#ifndef BUDDY_H
+#define BUDDY_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+extern uintptr_t heap_start;
+extern uintptr_t heap_end;
+
+extern char __heap_start;
+extern char __heap_end;
+
+void  buddy_init(uintptr_t start, uintptr_t end);
+void *buddy_alloc(size_t size);
+int   buddy_free(void *ptr);
+
+/* Returns total heap memory managed by buddy allocator in bytes */
+static inline size_t buddy_total_bytes(void) {
+    return (uintptr_t)&__heap_end - (uintptr_t)&__heap_start;
+}
+
+#endif // BUDDY_H

kern/libkern/memory.c

@@ -1,28 +1,21 @@
+#include <assert.h>
 #include <memory.h>
-#include <string.h>
-#include <uart.h>
+#include <stdlib.h>
 
-#define MAX_PROBE_SIZE (256 * 1024 * 1024) // Probe up to 256 MiB max
-#define PROBE_STEP     0x1000              // Probe every 4 KiB page
+int memory_sweep(const uintptr_t start, const uintptr_t end) {
+    assert_msg(start < end, "Start needs to be before end.");
+    uintptr_t sweeper = start;
 
-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
+    while (sweeper < end) {
+        *(uint64_t *)sweeper = 0xFAFAFAFABCBCBCBC;
+        sweeper += sizeof(uint64_t);
     }
 
-        *addr = old; // restore original data
-        detected = offset + PROBE_STEP;
+    sweeper -= sizeof(uint64_t);
+    while (sweeper != start) {
+        assert(*(uint64_t *)sweeper == 0xFAFAFAFABCBCBCBC);
+        sweeper -= sizeof(uint64_t);
     }
 
-    return detected;
+    return EXIT_SUCCESS;
 }

kern/libkern/memory.h

@@ -8,9 +8,8 @@
 #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.
+ * Set and fetch routine for checking memory.
  */
-size_t probe_memory(void);
+int memory_sweep(const uintptr_t start, const uintptr_t end);
 
-#endif // MEMORY_KARNEL_H
+#endif // MEMORY_KERNEL_H

kern/libkern/panic.h

@@ -1,7 +1,7 @@
 #ifndef KERNEL_PANIC_H
 #define KERNEL_PANIC_H
 
-#define PANIC(fmt, ...) __panic("[Panic @ %s:%d %s] " fmt, __FILE__, __LINE__, __func__, ##__VA_ARGS__)
+#define PANIC(fmt, ...) __panic("[Panic @ %s:%d %s] " fmt "\n", __FILE__, __LINE__, __func__, ##__VA_ARGS__)
 
 void __panic(const char *restrict fmt, ...);
 

kern/start.c

@@ -1,6 +1,7 @@
+#include <assert.h>
 #include <banner.h>
+#include <buddy.h>
 #include <config.h>
-#include <kalloc.h>
 #include <memory.h>
 #include <panic.h>
 #include <proc.h>
@@ -8,6 +9,7 @@
 #include <spinlock.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <string.h>
 #include <uart.h>
 
 /**
@@ -39,7 +41,8 @@ void start() {
 
     if (id == 0) {
         /* Here we will do a bunch of initialization steps */
-        kalloc_init();
+        memory_sweep(heap_start, heap_end);
+        buddy_init(heap_start, heap_end);
         spinlock_init(&sl);
         for (int i = 0; i < banner_len; i++) uart_putc(banner[i]);
         __sync_synchronize();