replace stgMallocBytesRWX() with our own allocator

See bug #738

Allocating executable memory is getting more difficult these days.  In
particular, the default SELinux policy on Fedora Core 5 disallows
making the heap (i.e. malloc()'d memory) executable, although it does
apparently allow mmap()'ing anonymous executable memory by default.

Previously, stgMallocBytesRWX() used malloc() underneath, and then
tried to make the page holding the memory executable.  This was rather
hacky and fails with Fedora Core 5.  

This patch adds a mini-allocator for executable memory, based on the
block allocator.  We grab page-sized blocks and make them executable,
then allocate small objects from the page.  There's a simple free
function, that will free whole pages back to the system when they are
empty.

1 files changed, 52 insertions, 0 deletions

diff --git a/rts/posix/OSMem.c b/rts/posix/OSMem.c
new file mode 100644
index 0000000000..6e8337bdc6
--- /dev/null
+++ b/rts/posix/OSMem.c
@@ -0,0 +1,52 @@
+/* -----------------------------------------------------------------------------
+ *
+ * (c) The University of Glasgow 2006
+ *
+ * OS-specific memory management
+ *
+ * ---------------------------------------------------------------------------*/
+
+#include "Rts.h"
+#include "OSMem.h"
+
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/mman.h>
+
+/* no C99 header stdint.h on OpenBSD? */
+#if defined(openbsd_HOST_OS)
+typedef unsigned long my_uintptr_t;
+#else
+#include <stdint.h>
+typedef uintptr_t my_uintptr_t;
+#endif
+
+lnat getPageSize (void)
+{
+    static lnat pageSize = 0;
+    if (pageSize) {
+	return pageSize;
+    } else {
+	long ret;
+	ret = sysconf(_SC_PAGESIZE);
+	if (ret == -1) {
+	    barf("getPageSize: cannot get page size");
+	}
+	return ret;
+    }
+}
+
+void setExecutable (void *p, lnat len, rtsBool exec)
+{
+    my_uintptr_t pageSize = getPageSize();
+
+    /* malloced memory isn't executable by default on OpenBSD */
+    my_uintptr_t mask             = ~(pageSize - 1);
+    my_uintptr_t startOfFirstPage = ((my_uintptr_t)p          ) & mask;
+    my_uintptr_t startOfLastPage  = ((my_uintptr_t)p + len - 1) & mask;
+    my_uintptr_t size             = startOfLastPage - startOfFirstPage + pageSize;
+    if (mprotect((void*)startOfFirstPage, (size_t)size, 
+		 (exec ? PROT_EXEC : 0) | PROT_READ | PROT_WRITE) != 0) {
+	barf("makeExecutable: failed to protect 0x%p\n", p);
+    }
+}