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+/*******************************************************************************
+ mach_override.h
+ Copyright (c) 2003-2009 Jonathan 'Wolf' Rentzsch: <http://rentzsch.com>
+ Some rights reserved: <http://opensource.org/licenses/mit-license.php>
+
+ ***************************************************************************/
+
+/***************************************************************************//**
+ @mainpage mach_override
+ @author Jonathan 'Wolf' Rentzsch: <http://rentzsch.com>
+
+ 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+ Update: MakeDataExecutable() has been replaced by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
+ concern...
+ @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" {
+#endif
+
+/**
+ 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
+ function.
+ @param originalFunctionReentryIsland <- Optional pointer to pointer to the
+ reentry island. Can be nullptr.
+ @result <- err_cannot_override if the original
+ function's implementation begins with
+ the 'mfctr' instruction.
+
+ ************************************************************************************/
+
+ mach_error_t
+mach_override_ptr(
+ void *originalFunctionAddress,
+ const void *overrideFunctionAddress,
+ void **originalFunctionReentryIsland );
+
+/************************************************************************************//**
+
+
+ ************************************************************************************/
+
+#ifdef __cplusplus
+
+#define MACH_OVERRIDE( ORIGINAL_FUNCTION_RETURN_TYPE, ORIGINAL_FUNCTION_NAME, ORIGINAL_FUNCTION_ARGS, ERR ) \
+ { \
+ static ORIGINAL_FUNCTION_RETURN_TYPE (*ORIGINAL_FUNCTION_NAME##_reenter)ORIGINAL_FUNCTION_ARGS; \
+ 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; \
+ } \
+ static ORIGINAL_FUNCTION_RETURN_TYPE replacement ORIGINAL_FUNCTION_ARGS {
+
+#define END_MACH_OVERRIDE( ORIGINAL_FUNCTION_NAME ) \
+ } \
+ }; \
+ \
+ err = mach_override_class__##ORIGINAL_FUNCTION_NAME::override((void*)ORIGINAL_FUNCTION_NAME); \
+ }
+
+#endif
+
+#ifdef __cplusplus
+ }
+#endif
+#endif // _mach_override_