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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 #ifndef _WIN32
14 #include <sys/mman.h>
15 #endif
16 
17 /* #include "config.h"
18  * FIXME: CMake - include when cmake system is ready.
19  * Remove #define HAVE_SYSCONF 1 line.
20  */
21 #define HAVE_SYSCONF 1
22 
23 #ifdef _WIN32
24 #define WIN32_LEAN_AND_MEAN
25 #include <Windows.h>
26 #else
27 #ifndef __APPLE__
28 #include <unistd.h>
29 #endif /* __APPLE__ */
30 #endif /* _WIN32 */
31 
32 #if __LP64__
33 	#define TRAMPOLINE_SIZE 48
34 #else
35 	#define TRAMPOLINE_SIZE 40
36 #endif
37 
38 /*
39  * The compiler generates calls to __enable_execute_stack() when creating
40  * trampoline functions on the stack for use with nested functions.
41  * It is expected to mark the page(s) containing the address
42  * and the next 48 bytes as executable.  Since the stack is normally rw-
43  * that means changing the protection on those page(s) to rwx.
44  */
45 
46 COMPILER_RT_ABI void
__enable_execute_stack(void * addr)47 __enable_execute_stack(void* addr)
48 {
49 
50 #if _WIN32
51 	MEMORY_BASIC_INFORMATION mbi;
52 	if (!VirtualQuery (addr, &mbi, sizeof(mbi)))
53 		return; /* We should probably assert here because there is no return value */
54 	VirtualProtect (mbi.BaseAddress, mbi.RegionSize, PAGE_EXECUTE_READWRITE, &mbi.Protect);
55 #else
56 #if __APPLE__
57 	/* On Darwin, pagesize is always 4096 bytes */
58 	const uintptr_t pageSize = 4096;
59 #elif !defined(HAVE_SYSCONF)
60 #error "HAVE_SYSCONF not defined! See enable_execute_stack.c"
61 #else
62         const uintptr_t pageSize = sysconf(_SC_PAGESIZE);
63 #endif /* __APPLE__ */
64 
65 	const uintptr_t pageAlignMask = ~(pageSize-1);
66 	uintptr_t p = (uintptr_t)addr;
67 	unsigned char* startPage = (unsigned char*)(p & pageAlignMask);
68 	unsigned char* endPage = (unsigned char*)((p+TRAMPOLINE_SIZE+pageSize) & pageAlignMask);
69 	size_t length = endPage - startPage;
70 	(void) mprotect((void *)startPage, length, PROT_READ | PROT_WRITE | PROT_EXEC);
71 #endif
72 }
73