Index: gc.c
===================================================================
--- gc.c	(revision 34318)
+++ gc.c	(working copy)
@@ -36,6 +36,9 @@
 
 #if defined _WIN32 || defined __CYGWIN__
 #include <windows.h>
+#elif defined(__OpenBSD__)
+/* workaround for OpenBSD broken posix_memalign() */
+#include <sys/mman.h>
 #elif defined(HAVE_POSIX_MEMALIGN)
 #elif defined(HAVE_MEMALIGN)
 #include <malloc.h>
@@ -1083,6 +1086,11 @@
     }
 }
 
+#if defined(__OpenBSD__)
+/* workaround for OpenBSD broken posix_memalign() */
+static st_table *am_size_table = NULL;
+#endif
+
 static void *
 aligned_malloc(size_t alignment, size_t size)
 {
@@ -1092,6 +1100,43 @@
     res = __mingw_aligned_malloc(size, alignment);
 #elif _WIN32 || defined __CYGWIN__
     res = _aligned_malloc(size, alignment);
+#elif defined(__OpenBSD__)
+    /* OpenBSD posix_memalign() is broken. Quoting BUGS in manual:
+     * "Only alignments up to the page size can be specified."
+     * This workaround assumes that
+     *  1. Ruby wants large alignment and large size.
+     *  2. OpenBSD mmap() tends to return random addresses.
+     *  3. OpenBSD mmap() tends to obey address hints. */
+    {
+        size_t mask;
+        int tries;
+        void *target;
+
+        mask = alignment - 1;
+        if (alignment & mask)
+            return NULL;  /* alignment is not power of 2 */
+        tries = 10;
+        while (tries--) {
+            /* find a random place in memory */
+            target = mmap(NULL, 1, PROT_READ|PROT_WRITE, MAP_ANON, -1, 0);
+            if (target == NULL)
+                return NULL;
+            munmap(target, 1);
+            /* align target */
+            target = (void *)((size_t)target & ~mask);
+            res = mmap(target, size, PROT_READ|PROT_WRITE, MAP_ANON, -1, 0);
+            if (res == target) {
+                /* success! */
+                if (!am_size_table)
+                    am_size_table = st_init_numtable();
+                st_insert(am_size_table, (st_data_t)res, size);
+                return res;
+            }
+            if (res != MAP_FAILED)
+                munmap(res, size);
+        }
+        return NULL;  /* no more tries */
+    }
 #elif defined(HAVE_POSIX_MEMALIGN)
     if (posix_memalign(&res, alignment, size) == 0) {
         return res;
@@ -1113,6 +1158,14 @@
     __mingw_aligned_free(ptr);
 #elif _WIN32 || defined __CYGWIN__
     _aligned_free(ptr);
+#elif defined(__OpenBSD__)
+    /* workaround for OpenBSD broken posix_memalign() */
+    {
+        st_data_t res, val;
+        res = (st_data_t)ptr;
+        if (am_size_table && st_delete(am_size_table, &res, &val))
+            munmap(ptr, (size_t)val);
+    }
 #else
     free(ptr);
 #endif