basic malloc() implementation

1 files changed, 68 insertions, 1 deletions

diff --git a/src/mapalloc.c b/src/mapalloc.c
index bde39f9..00af064 100644
--- a/src/mapalloc.c
+++ b/src/mapalloc.c
@@ -1,9 +1,37 @@
 #define _POSIX_C_SOURCE 200809L
-#include <sys/mman.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdint.h>
 #include <string.h>
+#include <sys/mman.h>
+#include <unistd.h>
 
 #include "mapalloc.h"
 
+#ifndef PAGESIZE
+static size_t get_pagesize(void)
+{
+	static size_t pagesize = 0;
+	if (pagesize == 0) {
+		pagesize = (size_t)sysconf(_SC_PAGESIZE);
+	}
+	return pagesize;
+}
+
+#define PAGESIZE get_pagesize()
+#endif
+
+struct bucket {
+	size_t used;
+	size_t allocated;
+};
+
+static struct bucket *get_bucket(void *ptr)
+{
+	uintptr_t addr = (uintptr_t)ptr;
+	return NULL;
+}
+
 void *map_calloc(size_t nelem, size_t elsize)
 {
 	size_t n = nelem * elsize;
@@ -18,6 +46,39 @@ void *map_calloc(size_t nelem, size_t elsize)
 
 void *map_malloc(size_t n)
 {
+	int fd = -1;
+	int prot = PROT_READ | PROT_WRITE;
+	int flags = MAP_PRIVATE;
+
+	/* round up to PAGESIZE, add 2 * PAGESIZE */
+	size_t alloc = n;
+	if (n % PAGESIZE != 0) {
+		alloc += n % PAGESIZE;
+	}
+	alloc += 2 * PAGESIZE;
+
+	#ifdef MAP_ANONYMOUS
+	flags = MAP_ANONYMOUS;
+	#else
+	fd = open("/dev/null", O_RDONLY);
+	#endif
+
+	void *ptr = mmap(NULL, alloc, prot, flags, fd, 0);
+
+	if (fd != -1) {
+		close(fd);
+	}
+
+	mprotect(ptr, PAGESIZE, PROT_NONE);
+	mprotect((char*)ptr + alloc - (2 * PAGESIZE), PAGESIZE, PROT_NONE);
+
+	/*
+	struct bucket *b = get_bucket(ptr);
+	b->used = n;
+	b->allocated = alloc;
+	*/
+
+	return ptr;
 }
 
 void *map_realloc(void *ptr, size_t n)
@@ -25,6 +86,7 @@ void *map_realloc(void *ptr, size_t n)
 	if (ptr == NULL) {
 		return map_malloc(n);
 	}
+	return NULL;
 }
 
 void map_free(void *ptr)
@@ -32,4 +94,9 @@ void map_free(void *ptr)
 	if (ptr == NULL) {
 		return;
 	}
+
+	struct bucket *b = get_bucket(ptr);
+	if (b == NULL) {
+		/* attempting to free() an invalid pointer */
+	}
 }