TweetFollow Us on Twitter

PowerPC Code
Volume Number:10
Issue Number:4
Column Tag:Powering Up

Connecting A 68k Object File
To PowerPC Code

A robust technique for loading and calling 68K modules from your PowerPC application

By Richard Clark, Apple Computer, Inc.

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

Many developers run into a major problem when porting code to PowerPC: incorporating 68K object models which came from an outside vendor. Since you can’t just hand a 68K module to the PowerPC linker, you have to find some alternative for loading the library and calling the library’s functions. Fortunately, developers can use the Code Fragment Manager and the Mixed Mode Manager together to solve this problem.

The solution involves creating a stand-alone version of the 68K code, then assembling a “jump table” of Universal Procedure Pointers which the application can use to call this code. Since applications (and, in fact, any PowerPC code fragment) can have global variables, it makes sense to allocate this table within the application. However, since the 68K library entry points are only available to the 68K code, that code has to create the universal procedure pointers. This would create an impossible dilemma except for one fact - both Mixed Mode and the Code Fragment Manager can be called from emulation on a Power Macintosh via A-Traps.

Thus we have a solution - the application must create the jump table as a global variable, and then pass its address to the 68K code which assembles the jump table. (An alternate method involves exporting the table from the application. The 68K code must open a connection back to the application, and ask the CFM for the address of the jump table.) The 68K code creates Universal Procedure Pointers to fill the table, which allows the application to call the library functions using Mixed Mode.

Creating the Jump Table

The first step is to prepare a list of all of the functions that your application calls in the library. Next, define ProcInfo values for each of these functions, using the MixedMode.h header and any header which defines callback functions (such as Controls.h) as a guide. You should also create macros for creating and calling a UniversalProcPtr in this way.

Next, create a data structure which contains Mixed Mode “Universal Procedure Pointers” for each of these functions. Put a copy of this data structure into a global variable in your PowerPC application, and don’t declare it as “static” (i.e. hidden.) You should also export this table, for a reason that will become clear shortly.


/* 1 */
// This is a header file common to the application and 68K code 

#include <ConditionalMacros.h>
#include <MixedMode.h>

typedef void (*CallbackPtr)(void); // A pointer which is fed to the library

typedef pascal OSErr (*Routine1ProcPtr)(CallbackPtr callbackRoutine);

enum {
 uppRoutine1ProcInfo = kPascalStackBased
  | RESULT_SIZE (SIZE_CODE(sizeof(OSErr)))
  | STACK_ROUTINE_PARAMETER(1, SIZE_CODE(sizeof(CallbackPtr)))
};

#if USESROUTINEDESCRIPTORS
// Use these definitions if we're compiling for Power Macintosh or another
// Macintosh system which supports Mixed Mode
typedef UniversalProcPtr Routine1UPP;

#define CallRoutine1Proc(userRoutine, longValue)         \
 CallUniversalProc((UniversalProcPtr)(userRoutine),\
 uppRoutine1ProcInfo, longValue)
#define NewRoutine1Proc(userRoutine) \
 (RoutineUPP) NewRoutineDescriptor((ProcPtr)userRoutine, \
    uppRoutine1ProcInfo, GetCurrentISA())
#else
// Use these definitions if we're compiling for a 68K-based Macintosh
typedef Routine1ProcPtr Routine1UPP;

#define CallRoutine1Proc(userRoutine, longValue)         \
 (*((Routine1ProcPtr )userRoutine))(longValue)
#define NewRoutine1Proc(userRoutine) \
 (Routine1UPP)(userRoutine)
#endif

 
// Here's the list of Universal Procedure Pointers
struct JumpTable {
 Routine1UPProutine1;
};

typedef struct JumpTable JumpTable, *JumpTablePtr;

// === Information on calling the 68K setup functions
typedef pascal OSErr (*SetupProcPtr)(JumpTablePtr);

enum {
 uppSetupProcInfo = kPascalStackBased
  | RESULT_SIZE (SIZE_CODE(sizeof(OSErr)))
  | STACK_ROUTINE_PARAMETER(1, SIZE_CODE(sizeof(JumpTablePtr)))
};

#if USESROUTINEDESCRIPTORS
// Use these definitions if we're compiling for Power Macintosh or another
// Macintosh system which supports Mixed Mode
typedef UniversalProcPtr SetupUPP;

#define CallSetupProc(userRoutine, jumpTableAddr)        \
 CallUniversalProc((UniversalProcPtr)(userRoutine),\
 uppSetupProcInfo, jumpTableAddr)
#define NewSetupProc(userRoutine)  \
 (SetupUPP) NewRoutineDescriptor((ProcPtr)userRoutine, \
    uppSetupProcInfo, GetCurrentISA())
#else
// Use these definitions if we're compiling for a 68K-based Macintosh
typedef SetupProcPtr SetupUPP;

#define CallSetupProc(userRoutine, jumpTableAddr)        \
 (*((SetupProcPtr)userRoutine))(jumpTableAddr)
#define NewSetupProc(userRoutine)  \
 (SetupUPP)(userRoutine)
#endif

Next, you have to create the “setup” function in 68K code and link it to your 68K object library. This routine needs to fill in each of the pointers in the table. The resulting code should be compiled, linked, and made into a stand-alone 68K code resource.

Granted, this technique could prove difficult if the library depends on having an A5 world. If your 68K library requires global variables, you must apply one of the special coding techniques documented in the Macintosh Developer Technical Notes or develop magazine.) Also note that if you want this code to run on a 68K machine, you should check for the presence of Mixed Mode and react appropriately.


/* 2 */
pascal OSErr BuildJumpTable(JumpTablePtr theJumpTable)
// Build a table of pointers to functions in our linked library
{
 OSErr  err;
 // Fill in the table with pointers to each library function
 theJumpTable->routine1 = NewMyRoutineProc(Routine1);
 err = MemError();
 return err;
}

The alternate approach involves exporting the jump table from the Application using the CFM, and letting the 68K code ask the CFM for the table’s address. Note the use of a STR# resource to store the application and table name strings - this avoids needing an A5 world just for the string constants. (Note that this code will not work on a machine which doesn’t have the Code Fragment Manager or Mixed Mode.)


/* 3 */
OSErr   err;
 JumpTablePtr  theJumpTable;
 ConnectionID  connID = 0;
 Ptr    mainAddr;
 Str255 errName, appName, tableName;
 SymClass symClass;
// Locate the application that called us
 GetIndString(&appName, 128, 1); // Assuming the name is in a STR#
 err = GetSharedLibrary(&appName, kPowerPCArch, 0, 
 &connID, &mainAddr, &errName);
 if (err) goto done;
 
 // Now, locate the shared table
 // (it's a pointer stored in a global variable)
 GetIndString(&tableName, 128, 2);// The table name is in the same STR#
 err = FindSymbol(connID, &tableName, 
 (Ptr*)&myTablePointer, &symClass);
 if (err) goto done;
// Insert the code to create UniversalProcPtrs here
done:
 if (connID)
 CloseConnection(&connID);
  return err;

To initialize this table, simply load the code resource from the application and call it via Mixed Mode. When the resource returns, the jump table will be full of Universal Procedure Pointers. Therefore, you should then modify your application to use Mixed Mode and the pointers in the table to call the library functions.


/* 4 */
// include the usual macros for creating a UniversalProcPtr for our callback 
routine
JumpTable gJumpTable;
// Load the stand-alone code
Handle  theResource;
theResource= Get1IndResource('STUB', 1);
if (theResource) {
  MoveHHi(theResource);
  HLock(theResource);// Lock it -- and NEVER unlock it
  // Call the entry point, no parameters
  CallSetupProc(*theResource, &gJumpTable);  
 // we know it's 68K, so we didn't
 // bother with creating a Routine Descriptor
  // Create a UniversalProcPtr for our callback routine
  CallbackUPP ourCallback;
  ourCallback = NewCallbackProc(MyCallbackRoutine);
  result = CallRoutine1Proc(gJumpTable.routine1,ourCallback );
  DisposeRoutineDescriptor(ourCallback);
}

Note that since the library function takes a callback pointer, we had to create a UniversalProcPtr and pass that instead of the address of the actual code. (If we hadn't done this, the machine would crash.) Since this causes memory to be allocated for a Routine Descriptor, we call DisposeRoutineDescriptor afterwards to release the memory.

That’s all there is to it! This is a robust technique which is now being used in several commercial applications - perhaps it will prove useful in yours.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

Combo Quest (Games)
Combo Quest 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Combo Quest is an epic, time tap role-playing adventure. In this unique masterpiece, you are a knight on a heroic quest to retrieve... | Read more »
Hero Emblems (Games)
Hero Emblems 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: ** 25% OFF for a limited time to celebrate the release ** ** Note for iPhone 6 user: If it doesn't run fullscreen on your device... | Read more »
Puzzle Blitz (Games)
Puzzle Blitz 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Puzzle Blitz is a frantic puzzle solving race against the clock! Solve as many puzzles as you can, before time runs out! You have... | Read more »
Sky Patrol (Games)
Sky Patrol 1.0.1 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0.1 (iTunes) Description: 'Strategic Twist On The Classic Shooter Genre' - Indie Game Mag... | Read more »
The Princess Bride - The Official Game...
The Princess Bride - The Official Game 1.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.1 (iTunes) Description: An epic game based on the beloved classic movie? Inconceivable! Play the world of The Princess Bride... | Read more »
Frozen Synapse (Games)
Frozen Synapse 1.0 Device: iOS iPhone Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Frozen Synapse is a multi-award-winning tactical game. (Full cross-play with desktop and tablet versions) 9/10 Edge 9/10 Eurogamer... | Read more »
Space Marshals (Games)
Space Marshals 1.0.1 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.1 (iTunes) Description: ### IMPORTANT ### Please note that iPhone 4 is not supported. Space Marshals is a Sci-fi Wild West adventure taking place... | Read more »
Battle Slimes (Games)
Battle Slimes 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: BATTLE SLIMES is a fun local multiplayer game. Control speedy & bouncy slime blobs as you compete with friends and family.... | Read more »
Spectrum - 3D Avenue (Games)
Spectrum - 3D Avenue 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: "Spectrum is a pretty cool take on twitchy/reaction-based gameplay with enough complexity and style to stand out from the... | Read more »
Drop Wizard (Games)
Drop Wizard 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Bring back the joy of arcade games! Drop Wizard is an action arcade game where you play as Teo, a wizard on a quest to save his... | Read more »

Price Scanner via MacPrices.net

Our MacBook Price Trackers will show you the...
Our Apple award-winning MacBook Price Trackers are continually updated with the latest information on prices, bundles, and availability for 16″ and 14″ MacBook Pros along with 13″ and 15″ MacBook... Read more
Amazon is offering a 10% discount on Apple’s...
Don’t pay full price! Amazon has 16-inch M4 Pro MacBook Pros (Silver and Black colors) on sale today for 10% off Apple’s MSRP. Shipping is free. These are the lowest prices currently available for 16... Read more
13-inch M4 MacBook Airs on sale for $150 off...
Amazon has new 13″ M4 MacBook Airs on sale for $150 off MSRP right now, starting at $849. Sale prices apply to most colors and configurations. Be sure to select Amazon as the seller, rather than a... Read more
15-inch M4 MacBook Airs on sale for $150 off...
Amazon has new 15″ M4 MacBook Airs on sale for $150 off Apple’s MSRP, starting at $1049. Be sure to select Amazon as the seller, rather than a third-party: – 15″ M4 MacBook Air (16GB/256GB): $1049, $... Read more
Amazon is offering a $50 discount on Apple’s...
Amazon has Apple’s 11th-generation A16 iPads in stock on sale for $50 (or a little more) off MSRP this week. Shipping is free: – 11″ 11th-generation 128GB WiFi iPads: $299 $50 off MSRP – 11″ 11th-... Read more
Clearance 13-inch M1 MacBook Airs available f...
Walmart has clearance, but new, Apple 13″ M1 MacBook Airs (8GB RAM, 256GB SSD) available online for $649, $360 off original MSRP, in Space Gray, Silver, and Gold colors. These are new MacBooks for... Read more
iPad minis on sale for $100 off Apple’s MSRP...
Amazon is offering $100 discounts (up to 20% off) on Apple’s newest 2024 WiFi iPad minis, each with free shipping. These are the lowest prices available for new minis among the Apple retailers we... Read more
AirPods Max headphones on sale for $479, $70...
Amazon has AirPods Max with USB-C on sale for $479.99 in all colors. Shipping is free. Their price is $70 off Apple’s MSRP, and it’s the lowest price available today for AirPods Max. Keep an eye on... Read more
14-inch M4 Pro/M4 Max MacBook Pros on sale th...
Don’t pay full price! Get a new 14″ MacBook Pro with an M4 Pro or M4 Max CPU for up to $320 off Apple’s MSRP this weekend at these retailers…they are the lowest prices available for these MacBook... Read more
Get a 15-inch M4 MacBook Air for $150 off App...
A couple of Apple retailers are offering $150 discounts on new 15″ M4 MacBook Airs this weekend. Prices at these retailers start at $1049: (1): Amazon has new 15″ M4 MacBook Airs on sale for $150 off... Read more

Jobs Board

All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.