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Copyright (c) 2003-2009 Jonathan 'Wolf' Rentzsch: <>
Some rights reserved: <>
@mainpage mach_override
@author Jonathan 'Wolf' Rentzsch: <>
This package, coded in C to the Mach API, allows you to override ("patch")
program- and system-supplied functions at runtime. You can fully replace
functions with your implementations, or merely head- or tail-patch the
original implementations.
Use it by #include'ing mach_override.h from your .c, .m or .mm file(s).
@todo Discontinue use of Carbon's MakeDataExecutable() and
CompareAndSwap() calls and start using the Mach equivalents, if they
exist. If they don't, write them and roll them in. That way, this
code will be pure Mach, which will make it easier to use everywhere.
Update: MakeDataExecutable() has been replaced by
msync(MS_INVALIDATE). There is an OSCompareAndSwap in libkern, but
I'm currently unsure if I can link against it. May have to roll in
my own version...
@todo Stop using an entire 4K high-allocated VM page per 28-byte escape
branch island. Done right, this will dramatically speed up escape
island allocations when they number over 250. Then again, if you're
overriding more than 250 functions, maybe speed isn't your main
@todo Add detection of: b, bl, bla, bc, bcl, bcla, bcctrl, bclrl
first-instructions. Initially, we should refuse to override
functions beginning with these instructions. Eventually, we should
dynamically rewrite them to make them position-independent.
@todo Write mach_unoverride(), which would remove an override placed on a
function. Must be multiple-override aware, which means an almost
complete rewrite under the covers, because the target address can't
be spread across two load instructions like it is now since it will
need to be atomically updatable.
@todo Add non-rentry variants of overrides to test_mach_override.
#ifndef _mach_override_
#define _mach_override_
#include <sys/types.h>
#include <mach/error.h>
#ifdef __cplusplus
extern "C" {
Returned if the function to be overrided begins with a 'mfctr' instruction.
#define err_cannot_override (err_local|1)
Dynamically overrides the function implementation referenced by
originalFunctionAddress with the implentation pointed to by overrideFunctionAddress.
Optionally returns a pointer to a "reentry island" which, if jumped to, will resume
the original implementation.
@param originalFunctionAddress -> Required address of the function to
override (with overrideFunctionAddress).
@param overrideFunctionAddress -> Required address to the overriding
@param originalFunctionReentryIsland <- Optional pointer to pointer to the
reentry island. Can be NULL.
@result <- err_cannot_override if the original
function's implementation begins with
the 'mfctr' instruction.
void *originalFunctionAddress,
const void *overrideFunctionAddress,
void **originalFunctionReentryIsland );
#ifdef __cplusplus
{ \
static bool ORIGINAL_FUNCTION_NAME##_overriden = false; \
class mach_override_class__##ORIGINAL_FUNCTION_NAME { \
public: \
static kern_return_t override(void *originalFunctionPtr) { \
kern_return_t result = err_none; \
if (!ORIGINAL_FUNCTION_NAME##_overriden) { \
ORIGINAL_FUNCTION_NAME##_overriden = true; \
result = mach_override_ptr( (void*)originalFunctionPtr, \
(void*)mach_override_class__##ORIGINAL_FUNCTION_NAME::replacement, \
(void**)&ORIGINAL_FUNCTION_NAME##_reenter ); \
} \
return result; \
} \
} \
}; \
err = mach_override_class__##ORIGINAL_FUNCTION_NAME::override((void*)ORIGINAL_FUNCTION_NAME); \
#ifdef __cplusplus
#endif // _mach_override_