add memory allocation functions

Signed-off-by: Mattias Andrée <maandree@operamail.com>

1 files changed, 143 insertions, 6 deletions

diff --git a/src/slibc-alloc.c b/src/slibc-alloc.c
index a29b188..0cbf623 100644
--- a/src/slibc-alloc.c
+++ b/src/slibc-alloc.c
@@ -18,6 +18,13 @@
 #include <slibc-alloc.h>
 #include <stdlib.h>
 #include <strings.h>
+#include <errno.h>
+#include <sys/mman.h>
+
+
+
+#define PURE_ALLOC(p)  (((char*)(p)) - sizeof(size_t))
+#define PURE_SIZE(z)  ((z) + sizeof(size_t))
 
 
 
@@ -29,7 +36,9 @@
  */
 void fast_free(void* segment)
 {
-  free(segment);
+  if (segument == NULL)
+    return;
+  munmap(PURE_ALLOC(segment), PURE_SIZE(*(size_t*)segment));
 }
 
 
@@ -41,10 +50,138 @@ void fast_free(void* segment)
  */
 void secure_free(void* segment)
 {
-  if (segment)
-    {
-      explicit_bzero(segment, allocsize(segment));
-      free(segment);
-    }
+  if (segument == NULL)
+    return;
+  explicit_bzero(PURE_ALLOC(segment), PURE_SIZE(allocsize(segment)));
+  fast_free(segment);
+}
+
+
+/**
+ * This function returns the allocation size of
+ * a memory segment.
+ * 
+ * `p = malloc(n), allocsize(p)` will return `n`.
+ * 
+ * @param   segment  The memory segment.
+ * @return           The size of the memory segment, 0 on error.
+ * 
+ * @throws  EINVAL  If `segment` is `NULL`.
+ * @throws  EFAULT  If `segment` is not a pointer to an allocation
+ *                  on the heap, or was not allocated with a function
+ *                  implemented in slibc. It is however not guaranteed
+ *                  that this will happen, undefined behaviour may be
+ *                  invoked instead.
+ */
+size_t allocsize(void* segment)
+{
+  if (segment == NULL)
+    return errno = EINVAL, 0;
+  return *(size_t*)PURE_ALLOC(segment);
+}
+
+
+/**
+ * Common code for realloc-functions, apart from `naive_realloc`.
+ */
+#define REALLOC(ptr, size, CLEAR_OLD, CLEAR_NEW, CLEAR_FREE)	\
+  size_t old_size;						\
+  void* new_ptr;						\
+								\
+  if (size == 0)						\
+    return secure_free(ptr), NULL;				\
+			   					\
+  if (ptr == NULL)	   					\
+    return CLEAR_NEW ? malloc(size) : calloc(1, size);		\
+			   					\
+  old_size = allocsize(ptr);					\
+  if (old_size == size)						\
+    return ptr;							\
+								\
+  if (CLEAR_OLD ? (old_size > size) : 0)			\
+    explicit_bzero(((char*)ptr) + size, old_size - size);	\
+								\
+  new_ptr = naive_realloc(ptr);					\
+  if (new_ptr != ptr)						\
+    {								\
+      if (CLEAR_FREE)						\
+	explicit_bzero(PURE_ALLOC(ptr), PURE_SIZE(old_size));	\
+      fast_free(new_ptr);					\
+    }								\
+								\
+  if (CLEAR_NEW ? (old_size < size) : 0)			\
+    explicit_bzero(((char*)new_ptr) + old, size - old_size);	\
+								\
+  return new_ptr
+
+
+/**
+ * Variant of `realloc` that overrides newly allocated space
+ * with zeroes. Additionally, it will override any freed space
+ * with zeroes, including the old allocation if it creates a
+ * new allocation.
+ * 
+ * @param   ptr   The old allocation, see `realloc` for more details.
+ * @param   size  The new allocation size, see `realloc` for more details.
+ * @return        The new allocation, see `realloc` for more details.
+ * 
+ * @throws  ENOMEM  The process cannot allocate more memory.
+ */
+void* crealloc(void* ptr, size_t size)
+{
+  REALLOC(ptr, size, 1, 1, 1);
+}
+
+
+/**
+ * This function behaves exactly like `realloc`, except it is
+ * guaranteed to never initialise or errors data.
+ * 
+ * @param   ptr   The old allocation, see `realloc` for more details.
+ * @param   size  The new allocation size, see `realloc` for more details.
+ * @return        The new allocation, see `realloc` for more details.
+ * 
+ * @throws  ENOMEM  The process cannot allocate more memory.
+ */
+void* fast_realloc(void* ptr, size_t size)
+{
+  REALLOC(ptr, size, 0, 0, 0);
+}
+
+
+/**
+ * This function behaves exactly like `crealloc`, except it
+ * does not initialise newly allocated size.
+ * 
+ * @param   ptr   The old allocation, see `realloc` for more details.
+ * @param   size  The new allocation size, see `realloc` for more details.
+ * @return        The new allocation, see `realloc` for more details.
+ * 
+ * @throws  ENOMEM  The process cannot allocate more memory.
+ */
+void* secure_realloc(void* ptr, size_t size)
+{
+  REALLOC(ptr, size, 1, 0, 1);
+}
+
+
+/**
+ * This function behaves exactly like `fast_realloc`, except:
+ * - Its haviour is undefined if `ptr` is `NULL`.
+ * - Its haviour is undefined `size` equals the old allocation size.
+ * - Its haviour is undefined if `size` is zero.
+ * - It will never free `ptr`.
+ * 
+ * @param   ptr   The old allocation, see `realloc` for more details.
+ * @param   size  The new allocation size, see `realloc` for more details.
+ * @return        The new allocation, see `realloc` for more details.
+ * 
+ * @throws  ENOMEM  The process cannot allocate more memory.
+ */
+void* naive_realloc(void* ptr, size_t size)
+{
+  /* TODO improve implementation of naive_realloc */
+  return malloc(size);
+  (void) ptr;
 }