override_example.c

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#include <CoreServices/CoreServices.h>
#include "mach_override.h"

//  Funky Protos.
int original( int input );
int override( int input );
void* myMalloc( size_t size );

//  Reentry types & globals.
typedef int (*OriginalFunctionPtrType)( int );
OriginalFunctionPtrType gOriginalReentry;
typedef void* (*mallocFunctionPtrType)( size_t );
mallocFunctionPtrType   gMalloc;

int main (int argc, const char * argv[]) {
    //-------------------------------------------------
    //  Override a local function.
    
    //  Call it normally.
    printf( "*** normal:\n" );
    original( 10 );
    
    //  Override it.
    kern_return_t err = mach_override( "_original", NULL, &override, (void**) &gOriginalReentry );
    if( err )
        return err;
    
    //  Call it again, the same way.
    printf( "*** overriden:\n" );
    original( 10 );
    
    //-------------------------------------------------
    //  Override a system function.
    
    //  Override it.
    err = mach_override( "_malloc", NULL, &myMalloc, (void**) &gMalloc );
    if( err )
        return err;
    
    //  Call it normally.
    printf( "*** malloc overriden:\n" );
    malloc( 22 );
    
    
    return 0;
}

int original( int input ) {
    printf( "original input: %d\n", input );
    int result = input + 1;
    printf( "original result: %d\n", result );
    fflush( 0 );
    return result;
}

int override( int input ) {
    printf( "override input: %d\n", input );
    fflush( 0 );
    int result = (gOriginalReentry( input + 20 )) - 10;
    printf( "override result: %d\n", result );
    fflush( 0 );
    return result;
}

void* myMalloc( size_t size ) {
    void *result = gMalloc( size );
    printf( "myMalloc( size: %ld ); result: %p\n", size, result );
    return result;
}

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