1 /* ===-- enable_execute_stack.c - Implement __enable_execute_stack ---------===
3 * The LLVM Compiler Infrastructure
5 * This file is dual licensed under the MIT and the University of Illinois Open
6 * Source Licenses. See LICENSE.TXT for details.
8 * ===----------------------------------------------------------------------===
15 /* #include "config.h"
16 * FIXME: CMake - include when cmake system is ready.
17 * Remove #define HAVE_SYSCONF 1 line.
19 #define HAVE_SYSCONF 1
23 #endif /* __APPLE__ */
26 #define TRAMPOLINE_SIZE 48
28 #define TRAMPOLINE_SIZE 40
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.
39 void __enable_execute_stack(void* addr)
43 /* On Darwin, pagesize is always 4096 bytes */
44 const uintptr_t pageSize = 4096;
45 #elif !defined(HAVE_SYSCONF)
46 #error "HAVE_SYSCONF not defined! See enable_execute_stack.c"
48 const uintptr_t pageSize = sysconf(_SC_PAGESIZE);
49 #endif /* __APPLE__ */
51 const uintptr_t pageAlignMask = ~(pageSize-1);
52 uintptr_t p = (uintptr_t)addr;
53 unsigned char* startPage = (unsigned char*)(p & pageAlignMask);
54 unsigned char* endPage = (unsigned char*)((p+TRAMPOLINE_SIZE+pageSize) & pageAlignMask);
55 size_t length = endPage - startPage;
56 (void) mprotect((void *)startPage, length, PROT_READ | PROT_WRITE | PROT_EXEC);