1 files changed, 58 insertions, 0 deletions
diff --git a/lib/builtins/enable_execute_stack.c b/lib/builtins/enable_execute_stack.c
new file mode 100644
index 000000000000..63d836b31d17
--- /dev/null
+++ b/lib/builtins/enable_execute_stack.c
@@ -0,0 +1,58 @@
+/* ===-- enable_execute_stack.c - Implement __enable_execute_stack ---------===
+ *
+ *                     The LLVM Compiler Infrastructure
+ *
+ * This file is dual licensed under the MIT and the University of Illinois Open
+ * Source Licenses. See LICENSE.TXT for details.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+#include "int_lib.h"
+
+#include <sys/mman.h>
+
+/* #include "config.h"
+ * FIXME: CMake - include when cmake system is ready.
+ * Remove #define HAVE_SYSCONF 1 line.
+ */
+#define HAVE_SYSCONF 1
+
+#ifndef __APPLE__
+#include <unistd.h>
+#endif /* __APPLE__ */
+
+#if __LP64__
+	#define TRAMPOLINE_SIZE 48
+#else
+	#define TRAMPOLINE_SIZE 40
+#endif
+
+/*
+ * The compiler generates calls to __enable_execute_stack() when creating 
+ * trampoline functions on the stack for use with nested functions.
+ * It is expected to mark the page(s) containing the address 
+ * and the next 48 bytes as executable.  Since the stack is normally rw-
+ * that means changing the protection on those page(s) to rwx. 
+ */
+
+COMPILER_RT_ABI void
+__enable_execute_stack(void* addr)
+{
+
+#if __APPLE__
+	/* On Darwin, pagesize is always 4096 bytes */
+	const uintptr_t pageSize = 4096;
+#elif !defined(HAVE_SYSCONF)
+#error "HAVE_SYSCONF not defined! See enable_execute_stack.c"
+#else
+        const uintptr_t pageSize = sysconf(_SC_PAGESIZE);
+#endif /* __APPLE__ */
+
+	const uintptr_t pageAlignMask = ~(pageSize-1);
+	uintptr_t p = (uintptr_t)addr;
+	unsigned char* startPage = (unsigned char*)(p & pageAlignMask);
+	unsigned char* endPage = (unsigned char*)((p+TRAMPOLINE_SIZE+pageSize) & pageAlignMask);
+	size_t length = endPage - startPage;
+	(void) mprotect((void *)startPage, length, PROT_READ | PROT_WRITE | PROT_EXEC);
+}