1/* ===-- enable_execute_stack.c - Implement __enable_execute_stack ---------===
2 *
3 *                     The LLVM Compiler Infrastructure
4 *
5 * This file is distributed under the University of Illinois Open Source
6 * License. See LICENSE.TXT for details.
7 *
8 * ===----------------------------------------------------------------------===
9 */
10
11#include <stdint.h>
12#include <sys/mman.h>
13
14/* #include "config.h"
15 * FIXME: CMake - include when cmake system is ready.
16 * Remove #define HAVE_SYSCONF 1 line.
17 */
18#define HAVE_SYSCONF 1
19
20#ifndef __APPLE__
21#include <unistd.h>
22#endif /* __APPLE__ */
23
24
25/*
26 * The compiler generates calls to __enable_execute_stack() when creating
27 * trampoline functions on the stack for use with nested functions.
28 * It is expected to mark the page(s) containing the address
29 * and the next 48 bytes as executable.  Since the stack is normally rw-
30 * that means changing the protection on those page(s) to rwx.
31 */
32
33void __enable_execute_stack(void* addr)
34{
35
36#if __APPLE__
37	/* On Darwin, pagesize is always 4096 bytes */
38	const uintptr_t pageSize = 4096;
39#elif !defined(HAVE_SYSCONF)
40#error "HAVE_SYSCONF not defined! See enable_execute_stack.c"
41#else
42        const uintptr_t pageSize = sysconf(_SC_PAGESIZE);
43#endif /* __APPLE__ */
44
45	const uintptr_t pageAlignMask = ~(pageSize-1);
46	uintptr_t p = (uintptr_t)addr;
47	unsigned char* startPage = (unsigned char*)(p & pageAlignMask);
48	unsigned char* endPage = (unsigned char*)((p+48+pageSize) & pageAlignMask);
49	size_t length = endPage - startPage;
50	(void) mprotect((void *)startPage, length, PROT_READ | PROT_WRITE | PROT_EXEC);
51}
52
53
54