foreign export dynamic for MacOS X

[Wolfgang Thaller]

I recently added PowerPC thunk creation to GHC, and I thought it 
would also be useful for hugs.

Cheers,

Wolfgang Thaller

--- for src/builtin.c:

struct thunk_data {
     struct thunk_data* next;
     struct thunk_data* prev;
     HugsStablePtr      stable;
#if defined(__ppc__)
     char               code[13*4];
#else
     char               code[16];
#endif
};

struct thunk_data* foreignThunks = 0;

static void* mkThunk(void* app, HugsStablePtr s) {
     struct thunk_data* thunk
         = (struct thunk_data*)malloc(sizeof(struct thunk_data));
     char* pc;
     if (!thunk) {
         /* ToDo: better cleanup */
         printf("Can't allocate thunk for foreign export dynamic\n");
         exit(1);
     }
     if (foreignThunks) { /* non-empty list */
         foreignThunks->prev = thunk;
     }
     thunk->next = foreignThunks;
     thunk->prev = 0;
     foreignThunks = thunk;
     thunk->stable = s;
     pc = &thunk->code[0];
#if defined(__i386__)
     /* 3 bytes: pushl (%esp) */
     *pc++ = 0xff; *pc++ = 0x34; *pc++ = 0x24;

     /* 8 bytes: movl s,4(%esp) */
     *pc++ = 0xc7; *pc++ = 0x44; *pc++ = 0x24; *pc++ = 0x04;
     *((HugsStablePtr*)pc)++ = s;

     /* 5 bytes: jmp app */
     *pc++ = 0xe9;
     *((int*)pc)++ = (char*)app - ((char*)&(thunk->code[16]));
#elif defined(__ppc__) && defined(__GNUC__)
     /* This is only for MacOS X.
      * It does not work on MacOS 9 because of the very strange
      * handling of function pointers in OS 9.
      * I don't know about LinuxPPC calling conventions.
      * Please note that it only works for up to 7 arguments.
      */

     {
         unsigned long *adj_code = (unsigned long*)pc;
         // make room for extra arguments
         adj_code[0] = 0x7d2a4b78;    //mr r10,r9
         adj_code[1] = 0x7d094378;    //mr r9,r8
         adj_code[2] = 0x7ce83b78;    //mr r8,r7
         adj_code[3] = 0x7cc73378;    //mr r7,r6
         adj_code[4] = 0x7ca62b78;    //mr r6,r5
         adj_code[5] = 0x7c852378;    //mr r5,r4
         adj_code[6] = 0x7c641b78;    //mr r4,r3

         adj_code[7] = 0x3c000000;	//lis r0,hi(app)
         adj_code[7] |= ((unsigned long)app) >> 16;

         adj_code[8] = 0x3c600000;	//lis r3,hi(s)
         adj_code[8] |= ((unsigned long)s) >> 16;

         adj_code[9] = 0x60000000;	//ori r0,r0,lo(app)
         adj_code[9] |= ((unsigned long)app) & 0xFFFF;

         adj_code[10] = 0x60630000;	//ori r3,r3,lo(s)
         adj_code[10] |= ((unsigned long)s) & 0xFFFF;

         adj_code[11] = 0x7c0903a6;	//mtctr r0
         adj_code[12] = 0x4e800420;	//bctr

         pc = (char*) &adj_code[13];

         // Flush the Instruction cache:
         //MakeDataExecutable(adjustor,4*13);
             /* This would require us to link with CoreServices.framework */
         {	/* this should do the same: */
             int n = 13;
             unsigned long *p = adj_code;
             while(n--)
             {
                 __asm__ volatile ("dcbf 0,%0\n\tsync\n\ticbi 0,%0"
                             : : "g" (p));
                 p++;
             }
             __asm__ volatile ("sync\n\tisync");
         }
     }
#else
     ERRMSG(0) "Foreign export dynamic is not supported on this architecture"
     EEND;
#endif
     assert(pc <= &thunk->code[0] + sizeof(thunk->code));
     return &thunk->code; /* a pointer into the middle of the thunk */
}