mmap anonymous

userland/c/malloc.c

@@ -5,18 +5,27 @@
 #include <stdlib.h>
 
 int main(void) {
-    size_t bytes = sizeof(int) * 2;
-    /* Allocate 2 ints. */
-    int *is = malloc(bytes);
+    int *is;
+    size_t nbytes = 2 * sizeof(*is);
+
+    /* Allocate 2 ints. Note that unlike traditional stack arrays (non-VLA)
+     * this value does not have to be determined at compile time! */
+    is = malloc(nbytes);
+
     /* This can happen for example if we ask for too much memory. */
     if (is == NULL) {
         perror("malloc");
         exit(EXIT_FAILURE);
     }
+
+    /* Write to and read from the allocated memory. */
     is[0] = 1;
+    is[1] = 2;
     assert(is[0] == 1);
+    assert(is[1] == 2);
+
     /* Free the allocated memory. */
     free(is);
+
     return EXIT_SUCCESS;
 }
-

userland/glibc/README.adoc

@@ -1 +0,0 @@
-This directory contains glibc extensions to POSIX / ANSI C.

userland/glibc/build

@@ -1 +0,0 @@
-../build

userland/glibc/test

@@ -1 +0,0 @@
-../test

userland/linux/mmap_anonymous.c

@@ -0,0 +1,40 @@
+/* https://cirosantilli.com/linux-kernel-module-cheat#mmap-map-anonymous */
+
+#define _GNU_SOURCE
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+int main(void) {
+    int *is;
+    size_t nbytes = 2 * sizeof(*is);
+
+    /* Allocate 2 ints. */
+    is = mmap(
+        NULL,
+        nbytes,
+        PROT_READ | PROT_WRITE,
+        MAP_SHARED | MAP_ANONYMOUS,
+        -1,
+        0
+    );
+
+    /* This can happen for example if we ask for too much memory. */
+    if (is == NULL) {
+        perror("mmap");
+        exit(EXIT_FAILURE);
+    }
+
+    /* Write to and read from the allocated memory. */
+    is[0] = 1;
+    is[1] = 2;
+    assert(is[0] == 1);
+    assert(is[1] == 2);
+
+    /* Free the allocated memory. */
+    munmap(is, nbytes);
+
+    return EXIT_SUCCESS;
+}

userland/posix/mmap_file.c

@@ -1,13 +1,4 @@
-/* https://cirosantilli.com/linux-kernel-module-cheat#mmap
- *
- * Example of mmap on files.
- *
- * Create a file, mmap to it, write to maped memory, close.
- *
- * Then read the file and confirm it was written to.
- *
- * Implemented in Linux by the mmap syscall.
- */
+/* https://cirosantilli.com/linux-kernel-module-cheat#mmap-file */
 
 #define _XOPEN_SOURCE 700
 #include <assert.h>