compiler-rt/lib/builtins/enable_execute_stack.c

   1 //===-- enable_execute_stack.c - Implement __enable_execute_stack ---------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "int_lib.h"
  10
  11 #ifndef _WIN32
  12 #include <sys/mman.h>
  13 #endif
  14
  15 // #include "config.h"
  16 // FIXME: CMake - include when cmake system is ready.
  17 // Remove #define HAVE_SYSCONF 1 line.
  18 #define HAVE_SYSCONF 1
  19
  20 #ifdef _WIN32
  21 #define WIN32_LEAN_AND_MEAN
  22 #include <windows.h>
  23 #else
  24 #ifndef __APPLE__
  25 #include <unistd.h>
  26 #endif // __APPLE__
  27 #endif // _WIN32
  28
  29 #if __LP64__
  30 #define TRAMPOLINE_SIZE 48
  31 #else
  32 #define TRAMPOLINE_SIZE 40
  33 #endif
  34
  35 // The compiler generates calls to __enable_execute_stack() when creating
  36 // trampoline functions on the stack for use with nested functions.
  37 // It is expected to mark the page(s) containing the address
  38 // and the next 48 bytes as executable.  Since the stack is normally rw-
  39 // that means changing the protection on those page(s) to rwx.
  40
  41 COMPILER_RT_ABI void __enable_execute_stack(void *addr) {
  42
  43 #if _WIN32
  44   MEMORY_BASIC_INFORMATION mbi;
  45   if (!VirtualQuery(addr, &mbi, sizeof(mbi)))
  46     return; // We should probably assert here because there is no return value
  47   VirtualProtect(mbi.BaseAddress, mbi.RegionSize, PAGE_EXECUTE_READWRITE,
  48                  &mbi.Protect);
  49 #else
  50 #if __APPLE__
  51   // On Darwin, pagesize is always 4096 bytes
  52   const uintptr_t pageSize = 4096;
  53 #elif !defined(HAVE_SYSCONF)
  54 #error "HAVE_SYSCONF not defined! See enable_execute_stack.c"
  55 #else
  56   const uintptr_t pageSize = sysconf(_SC_PAGESIZE);
  57 #endif // __APPLE__
  58
  59   const uintptr_t pageAlignMask = ~(pageSize - 1);
  60   uintptr_t p = (uintptr_t)addr;
  61   unsigned char *startPage = (unsigned char *)(p & pageAlignMask);
  62   unsigned char *endPage =
  63       (unsigned char *)((p + TRAMPOLINE_SIZE + pageSize) & pageAlignMask);
  64   size_t length = endPage - startPage;
  65   (void)mprotect((void *)startPage, length, PROT_READ | PROT_WRITE | PROT_EXEC);
  66 #endif
  67 }