1 /* ===-- enable_execute_stack.c - Implement __enable_execute_stack ---------===
2  *
3  *                     The LLVM Compiler Infrastructure
4  *
5  * This file is dual licensed under the MIT and the University of Illinois Open
6  * Source Licenses. See LICENSE.TXT for details.
7  *
8  * ===----------------------------------------------------------------------===
9  */
10 
11 #include "int_lib.h"
12 
13 #include <sys/mman.h>
14 
15 /* #include "config.h"
16  * FIXME: CMake - include when cmake system is ready.
17  * Remove #define HAVE_SYSCONF 1 line.
18  */
19 #define HAVE_SYSCONF 1
20 
21 #ifndef __APPLE__
22 #include <unistd.h>
23 #endif /* __APPLE__ */
24 
25 #if __LP64__
26 	#define TRAMPOLINE_SIZE 48
27 #else
28 	#define TRAMPOLINE_SIZE 40
29 #endif
30 
31 /*
32  * The compiler generates calls to __enable_execute_stack() when creating
33  * trampoline functions on the stack for use with nested functions.
34  * It is expected to mark the page(s) containing the address
35  * and the next 48 bytes as executable.  Since the stack is normally rw-
36  * that means changing the protection on those page(s) to rwx.
37  */
38 
39 COMPILER_RT_ABI void
__enable_execute_stack(void * addr)40 __enable_execute_stack(void* addr)
41 {
42 
43 #if __APPLE__
44 	/* On Darwin, pagesize is always 4096 bytes */
45 	const uintptr_t pageSize = 4096;
46 #elif !defined(HAVE_SYSCONF)
47 #error "HAVE_SYSCONF not defined! See enable_execute_stack.c"
48 #else
49         const uintptr_t pageSize = sysconf(_SC_PAGESIZE);
50 #endif /* __APPLE__ */
51 
52 	const uintptr_t pageAlignMask = ~(pageSize-1);
53 	uintptr_t p = (uintptr_t)addr;
54 	unsigned char* startPage = (unsigned char*)(p & pageAlignMask);
55 	unsigned char* endPage = (unsigned char*)((p+TRAMPOLINE_SIZE+pageSize) & pageAlignMask);
56 	size_t length = endPage - startPage;
57 	(void) mprotect((void *)startPage, length, PROT_READ | PROT_WRITE | PROT_EXEC);
58 }
59