src/compiler-rt/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 #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
  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 }