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 __enable_execute_stack(void * addr)39void __enable_execute_stack(void* addr) 40 { 41 42 #if __APPLE__ 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" 47 #else 48 const uintptr_t pageSize = sysconf(_SC_PAGESIZE); 49 #endif /* __APPLE__ */ 50 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); 57 } 58 59 60