lib/builtins/enable_execute_stack.c

   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
  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 }