xpcom/build/mach_override.h

   1 /*******************************************************************************
   2         mach_override.h
   3                 Copyright (c) 2003-2009 Jonathan 'Wolf' Rentzsch: <http://rentzsch.com>
   4                 Some rights reserved: <http://opensource.org/licenses/mit-license.php>
   5
   6         ***************************************************************************/
   7
   8 /***************************************************************************//**
   9         @mainpage       mach_override
  10         @author         Jonathan 'Wolf' Rentzsch: <http://rentzsch.com>
  11
  12         This package, coded in C to the Mach API, allows you to override ("patch")
  13         program- and system-supplied functions at runtime. You can fully replace
  14         functions with your implementations, or merely head- or tail-patch the
  15         original implementations.
  16
  17         Use it by #include'ing mach_override.h from your .c, .m or .mm file(s).
  18
  19         @todo   Discontinue use of Carbon's MakeDataExecutable() and
  20                         CompareAndSwap() calls and start using the Mach equivalents, if they
  21                         exist. If they don't, write them and roll them in. That way, this
  22                         code will be pure Mach, which will make it easier to use everywhere.
  23                         Update: MakeDataExecutable() has been replaced by
  24                         msync(MS_INVALIDATE). There is an OSCompareAndSwap in libkern, but
  25                         I'm currently unsure if I can link against it. May have to roll in
  26                         my own version...
  27         @todo   Stop using an entire 4K high-allocated VM page per 28-byte escape
  28                         branch island. Done right, this will dramatically speed up escape
  29                         island allocations when they number over 250. Then again, if you're
  30                         overriding more than 250 functions, maybe speed isn't your main
  31                         concern...
  32         @todo   Add detection of: b, bl, bla, bc, bcl, bcla, bcctrl, bclrl
  33                         first-instructions. Initially, we should refuse to override
  34                         functions beginning with these instructions. Eventually, we should
  35                         dynamically rewrite them to make them position-independent.
  36         @todo   Write mach_unoverride(), which would remove an override placed on a
  37                         function. Must be multiple-override aware, which means an almost
  38                         complete rewrite under the covers, because the target address can't
  39                         be spread across two load instructions like it is now since it will
  40                         need to be atomically updatable.
  41         @todo   Add non-rentry variants of overrides to test_mach_override.
  42
  43         ***************************************************************************/
  44
  45 #ifndef         _mach_override_
  46 #define         _mach_override_
  47
  48 #include <sys/types.h>
  49 #include <mach/error.h>
  50
  51 #ifdef  __cplusplus
  52         extern  "C"     {
  53 #endif
  54
  55 /**
  56         Returned if the function to be overrided begins with a 'mfctr' instruction.
  57 */
  58 #define err_cannot_override     (err_local|1)
  59
  60 /************************************************************************************//**
  61         Dynamically overrides the function implementation referenced by
  62         originalFunctionAddress with the implentation pointed to by overrideFunctionAddress.
  63         Optionally returns a pointer to a "reentry island" which, if jumped to, will resume
  64         the original implementation.
  65
  66         @param  originalFunctionAddress                 ->      Required address of the function to
  67                                                                                                 override (with overrideFunctionAddress).
  68         @param  overrideFunctionAddress                 ->      Required address to the overriding
  69                                                                                                 function.
  70         @param  originalFunctionReentryIsland   <-      Optional pointer to pointer to the
  71                                                                                                 reentry island. Can be nullptr.
  72         @result                                                                 <-      err_cannot_override if the original
  73                                                                                                 function's implementation begins with
  74                                                                                                 the 'mfctr' instruction.
  75
  76         ************************************************************************************/
  77
  78     mach_error_t
  79 mach_override_ptr(
  80         void *originalFunctionAddress,
  81     const void *overrideFunctionAddress,
  82     void **originalFunctionReentryIsland );
  83
  84 /************************************************************************************//**
  85
  86
  87         ************************************************************************************/
  88
  89 #ifdef  __cplusplus
  90
  91 #define MACH_OVERRIDE( ORIGINAL_FUNCTION_RETURN_TYPE, ORIGINAL_FUNCTION_NAME, ORIGINAL_FUNCTION_ARGS, ERR )                     \
  92         {                                                                                                                                                                                                                               \
  93                 static ORIGINAL_FUNCTION_RETURN_TYPE (*ORIGINAL_FUNCTION_NAME##_reenter)ORIGINAL_FUNCTION_ARGS;                         \
  94                 static bool ORIGINAL_FUNCTION_NAME##_overriden = false;                                                                                                         \
  95                 class mach_override_class__##ORIGINAL_FUNCTION_NAME {                                                                                                           \
  96                 public:                                                                                                                                                                                                         \
  97                         static kern_return_t override(void *originalFunctionPtr) {                                                                                              \
  98                                 kern_return_t result = err_none;                                                                                                                                        \
  99                                 if (!ORIGINAL_FUNCTION_NAME##_overriden) {                                                                                                                      \
 100                                         ORIGINAL_FUNCTION_NAME##_overriden = true;                                                                                                              \
 101                                         result = mach_override_ptr( (void*)originalFunctionPtr,                                                                                 \
 102                                                                                                 (void*)mach_override_class__##ORIGINAL_FUNCTION_NAME::replacement,      \
 103                                                                                                 (void**)&ORIGINAL_FUNCTION_NAME##_reenter );                                            \
 104                                 }                                                                                                                                                                                                       \
 105                                 return result;                                                                                                                                                                          \
 106                         }                                                                                                                                                                                                               \
 107                         static ORIGINAL_FUNCTION_RETURN_TYPE replacement ORIGINAL_FUNCTION_ARGS {
 108
 109 #define END_MACH_OVERRIDE( ORIGINAL_FUNCTION_NAME )                                                                                                                                     \
 110                         }                                                                                                                                                                                                               \
 111                 };                                                                                                                                                                                                                      \
 112                                                                                                                                                                                                                                         \
 113                 err = mach_override_class__##ORIGINAL_FUNCTION_NAME::override((void*)ORIGINAL_FUNCTION_NAME);                           \
 114         }
 115
 116 #endif
 117
 118 #ifdef  __cplusplus
 119         }
 120 #endif
 121 #endif  //      _mach_override_