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Mar 96 Tips
Volume Number:12
Issue Number:3
Column Tag:Tips & Tidbits

Tips & Tidbits

By Steve Sisak, Contributing Editor

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

Calling PowerPC Code
From 68K Code

There is a lot of information out there about calling 68K code from PowerPC code, but there is very little about calling PowerPC code from 68K code.

Here is a nice method for calling PowerPC code from 68K code. I am using CodeWarrior 7. This is a bit lengthy so hang in there:

There are three steps required to get things up and running. Let’s look at a sample scenario:

You have a 68K application that you just can’t convert to PowerPC code (I don’t know why you can’t convert it, but just bear with me), but you can take some of the time-critical code and convert it to a PowerPC shared library and call it from the 68K code.

Suppose you have two functions that perform data compression:

long  CompressData(  unsigned char *inBuffer, 
 unsigned char *outBuffer,
 unsigned long inBufferSize );
   
long  UncompressData(unsigned char *inBuffer, 
 unsigned char *outBuffer, 
 unsigned long inBufferSize );

Step 1 - Create a PPC shared library containing your functions.

We are going to export these functions using the #pragma export directive. This is set in the PPC Prefs area of Codewarrior preferences.

“the shared library”
// Prototypes

#pragma export on

#ifdef __cplusplus
extern "C" {
#endif

long  CompressData(  unsigned char *inBuffer, 
 unsigned char *outBuffer, 
 unsigned long inBufferSize );
   
long  UncompressData(   unsigned char *inBuffer,
 unsigned char *outBuffer,
 unsigned long inBufferSize );

#ifdef __cplusplus
}
#endif

#pragma export off
// CompressData

long  CompressData( unsigned char *inBuffer, unsigned char 
   *outBuffer, unsigned long inBufferSize )
{
    ... compress data code
}

// UncompressData
   
long  UncompressData( unsigned char *inBuffer, unsigned char 
     *outBuffer, unsigned long inBufferSize )
{
    ... uncompress data code
}

Set the project type to a shared library and build the project. We now have a PowerPC shared library that we will use in Step 2.


Step 2 - Create a resource-based PEF Fragment that references our shared library.

We create a header file that defines some mixed mode information.

“the header file”
#ifdef __cplusplus
extern "C" {
#endif

typedef long (*CompressDataProcPtr)( unsigned char *inBuffer, 
 unsigned char *outBuffer, unsigned long inBufferSize );
typedef long (*UncompressDataProcPtr)( unsigned char *inBuffer, 
 unsigned char *outBuffer, unsigned long inBufferSize);

#if GENERATINGCFM || USESROUTINEDESCRIPTORS

typedef UniversalProcPtr CompressDataUPP;
typedef UniversalProcPtr UncompressDataUPP;

enum {
 uppCompressDataProcInfo = kCStackBased
 | RESULT_SIZE( SIZE_CODE( sizeof( long ) ) )
 | STACK_ROUTINE_PARAMETER( 1, SIZE_CODE( 
 sizeof( unsigned char *) ) )
 | STACK_ROUTINE_PARAMETER( 2, SIZE_CODE( 
 sizeof( unsigned char *) ) ) | STACK_ROUTINE_PARAMETER( 3, SIZE_CODE( 

 sizeof( long ) ) )
};

enum {
 uppUncompressDataProcInfo = kCStackBased
 | RESULT_SIZE( SIZE_CODE( sizeof( long ) ) )
 | STACK_ROUTINE_PARAMETER( 1, SIZE_CODE( 
 sizeof( unsigned char *) ) )
 | STACK_ROUTINE_PARAMETER( 2, SIZE_CODE( 
 sizeof( unsigned char *) ) )
 | STACK_ROUTINE_PARAMETER( 3, SIZE_CODE( 
 sizeof( long ) ) )
};

#else

typedef CompressDataProcPtr CompressDataUPP;
typedef UncompressDataProcPtr UncompressDataUPP;
#endif

//============================================================
// Extern Globals
//

#ifndef powerc

extern CompressDataUPP    myCompressDataUPP;
extern UncompressDataUPP  myUncompressDataUPP;

#endif

//============================================================
// Macros
//

#if GENERATINGPOWERPC || defined(powerc) || defined (__powerc)

#define myCompressData( a, b, c )  CompressData( a, b, c )
#define myUncompressData( a, b, c )UncompressData( a, b, c )

#else

#define myCompressData( a, b, c ) \  
 (*(CompressDataUPP)myCompressDataUPP( a, b, c )
#define myUncompressData( a, b, c  ) \
 (*(CompressDataUPP)myUncompressDataUPP( a, b, c )

#endif

//============================================================
// Prototypes
//

long CompressData( unsigned char *inBuffer, unsigned char 
    *outBuffer, unsigned long inBufferSize );
long UncompressData( unsigned char *inBuffer, unsigned char 
  *outBuffer, unsigned long inBufferSize );

#ifdef __cplusplus
}
#endif

Now we define the source file:

“the source file”
#include "the header file"

#ifdef __cplusplus
extern "C" {
#endif

#if GENERATINGPOWERPC || defined(powerc) || defined (__powerc)
#pragma options align=mac68k
#endif

#ifdef __CFM68K__
#pragma lib_export on
#endif

RoutineDescriptorCompressDataRD = 
 BUILD_ROUTINE_DESCRIPTOR(  uppCompressDataProcInfo, 
 CompressData );

RoutineDescriptorUncompressDataRD = 
 BUILD_ROUTINE_DESCRIPTOR(  uppUncompressDataProcInfo, 
 UncompressData );


#ifdef __CFM68K__
#pragma lib_export off
#endif

#if GENERATINGPOWERPC || defined(powerc) || defined (__powerc)
#pragma options align=reset
#endif

#ifdef __cplusplus
}
#endif

Add the shared library we built in Step 1 to this project.

Set the project type to shared library and build the project. We now have a PowerPC shared library that we want to convert to a resource. (Note: we don’t export this as a PowerPC code resource with no header, since we would get link errors for an undefined main entry.)

Open the file up in a resource editor and create a new resource (I use a type of 'PEF ', but any will do). Move the PEF code from the data fork into this resource. (If your resource editor will not do this, then it is a simple matter of creating a small application that will do this for you; this excercise is left for the reader.)

We now have a resource file that we will add to our 68K project.


Step 3 - Add 68K support code to your project

Your 68K project needs to have a bit of support code to get the code resource and load it in as a code fragment. Add to your code:

#include "the header file"

We need to declare some globals for the universal procs that will store the address of the routine descriptors. Add to your code:

#ifndef powerc
CompressDataUPP  myCompressDataUPP;
UncompressDataUPPmyUncompressDataUPP;
#endif

The following function takes care of checking for the existence of the CFM and Mixed Mode managers. We pass it a pointer to a CFragConnectionID variable and a Handle variable, which we will use later on for clean up. Add to your code:

#ifndef powerc

// SetupPPCNativeCode

OSErr SetupPPCNativeCode( CFragConnectionID *connID, 
 Handle *PEFHandle,
   ResType codeFragmentType, 
 short codeFragmentID )
{
 OSErr  theErr = noErr;
 long   templong;
 Str255 failedFragName;
 

    // get PEF container resource from our resource fork
 
 *PEFHandle = ::Get1Resource( codeFragmentType, codeFragmentID );
 theErr = ::ResError();
 if( !(*PEFHandle) )
 {
 if( theErr )  
 return( theErr );
 else
 return( ::MemError() );
 }
 
    // Check for Mixed Mode Manager and Code Fragment Manager (CFM)
 
 Boolean  hasMixedMode = !Gestalt( gestaltMixedModeAttr, 
 &templong );
 Boolean  hasCFM = !Gestalt( gestaltCFMAttr, &templong );
 
 theErr = Gestalt( gestaltSysArchitecture, &templong );
 if( ( theErr ) || 
 ( templong == gestalt68k ) ||
 ( !hasCFM ) ||
 ( !hasMixedMode ) )
 {
 ::ReleaseResource( *PEFHandle );
 return( -1 );
 }
 
 DetachResource( *PEFHandle );
 MoveHHi( *PEFHandle );
 HLock( *PEFHandle );
 
    // Assume this is PowerPC code, so it must be “prepared”
 
 theErr = ::GetMemFragment( (Ptr)**PEFHandle, 0, 0,            
 kNewCFragCopy, connID, 0, failedFragName );
 if( theErr )
 {
 DisposeHandle( *PEFHandle );
 return( theErr );
 }

 CFragSymbolClassmyClass;
 
 if( !theErr )
 theErr = ::FindSymbol( *connID, 
    (ConstStr255Param)"\pCompressDataRD", 
    (Ptr*)&myCompressDataUPP, 
    &myClass );
 if( !theErr )
 theErr = ::FindSymbol( *connID, 
    (ConstStr255Param)"\pUncompressDataRD", 
    (Ptr*)&myUncompressDataUPP, 
    &myClass );

 if( theErr )
 {
 DisposeHandle( *PEFHandle );
 return( theErr );
 }
 
 return( noErr );
}

The following function takes the connection id and handle returned from SetupPPCNativeCode, frees the connection and disposes of the handle. Add to your code:

// TearDownPPCNativeCode

void TearDownPPCNativeCode( CFragConnectionID connID, Handle PEFHandle 
)
{
 ::CloseConnection( &connID );
 if( PEFHandle )
 ::DisposeHandle( PEFHandle );
}

#endif

Build your 68K project as you normally would and be sure to include the resource file we created in Step 2 and ensure the the shared library we created in Step 1 is either in the Extensions folder of the System Folder or in the same directory as the application.

Here is what you would do the call the PowerPC code from 68K:

long PowerPC_Compress( unsigned char *inBuffer, unsigned char 
    *outBuffer, unsigned long inBufferSize )
{
 #ifndef powerc
 
    // For efficiency you would probably put this call in initialization code.
    // sConnID and sPEFHandle are static globals.
 
 OSErr err = SetupPPCNativeCode( &sConnID, &sPEFHandle, 
 'PEF ', 128 );
 if( err )
 return( 0 );  // We couldn’t compress anything so return 0
 #endif
 
 long   result = 0;
 
 result = myCompressData( inBuffer, outBuffer, inBufferSize );
 
 #ifndef powerc
 
    // For efficiency you would probably put this call in termination code.
 
 TearDownPPCNativeCode( sConnID, sPEFHandle );
 #endif
}

long PowerPC_Uncompress( unsigned char *inBuffer, 
 unsigned char *outBuffer, unsigned long inBufferSize )
{
 #ifndef powerc
 
    // For efficiency you would probably put this call in initialization code.
    // sConnID and sPEFHandle are static globals.
 
 OSErr err = SetupPPCNativeCode( &sConnID, &sPEFHandle, 
 'PEF ', 128 );
 if( err )
 return( 0 );  // We couldn’t compress anything so return 0
 #endif
 
 long   result = 0;
 
 result = myUncompressData( inBuffer, outBuffer, inBufferSize );
 
 #ifndef powerc
 
    // For efficiency you would probably put this call in termination code.
 
 TearDownPPCNativeCode( sConnID, sPEFHandle );
 #endif
}


That’s all there is to it. Enjoy and happy coding.

- Chris Rudolph

[BuildRoutineDescriptor() doesn’t work right with CFM68k; use NewRoutineDescriptor() instead. BuildRoutineDescriptor() generates code so you need to call MakeDataExecutable() after it. - sgs]

 
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