added new memory allocator files and README

allocator/bump_alloc/bump_alloc.c

@@ -0,0 +1,78 @@
+/**********************************
+ * bump_alloc.c
+ * Jeremy.Singer@glasgow.ac.uk
+ *
+ * This is a simple bump-pointer allocator.
+ * It mmaps a large buffer of SIZE bytes,
+ * then allocates this space in word-sized
+ * chunks to client code (in main fn).
+ *
+ * Initial simple memory allocator test.
+ * Explore capability narrowing operations
+ * and intrinsics for bound reporting.
+ */
+
+#include <cheriintrin.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+
+#include "bump_alloc.h"
+
+int count = 0;       /* number of bytes allocated so far*/
+int max = 0;         /* upper limit for count */
+char *buffer = NULL; /* the allocation buffer */
+
+void init_alloc(int size_in_bytes)
+{
+    /* request memory for our allocation buffer
+     * NB mmap min bounds for capability is 1 page (4K)
+     */
+    char *res = mmap(NULL, size_in_bytes, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0);
+
+    if (res == MAP_FAILED)
+    {
+        perror("error in initial mem allocation");
+        exit(-1);
+    }
+
+    buffer = res;
+    max = size_in_bytes;
+    return;
+}
+
+/*
+ * allocate len bytes with bump pointer allocator
+ * this is our simplistic `malloc` function
+ */
+char *malloc(int len)
+{
+    char *chunk = buffer + count;
+    size_t rounded_len; /* for CHERI alignment */
+    size_t new_count;   /* for buffer overflow check */
+
+    /* ensure we can represent the capability accurately,
+     * see p30 of CHERI C/C++ Prog Guide (June 2020)
+     * www.cl.cam.ac.uk/techreports/UCAM-CL-TR-947
+     */
+    chunk = __builtin_align_up(chunk, ~cheri_representable_alignment_mask(len) + 1);
+    rounded_len = cheri_representable_length(len);
+
+    new_count = (chunk + rounded_len) - buffer;
+    if (new_count > max)
+    {
+        /* out of bounds - don't allocate anything */
+        chunk = 0;
+    }
+    else
+    {
+        /* restrict capability range before returning ptr */
+        chunk = cheri_bounds_set_exact(chunk, rounded_len);
+
+        /* update bytes allocated count */
+        count = new_count;
+    }
+
+    return chunk;
+}