1 /* -----------------------------------------------------------------------------
2 * Foreign export adjustor thunks
6 * ---------------------------------------------------------------------------*/
8 /* A little bit of background...
10 An adjustor thunk is a dynamically allocated code snippet that allows
11 Haskell closures to be viewed as C function pointers.
13 Stable pointers provide a way for the outside world to get access to,
14 and evaluate, Haskell heap objects, with the RTS providing a small
15 range of ops for doing so. So, assuming we've got a stable pointer in
16 our hand in C, we can jump into the Haskell world and evaluate a callback
17 procedure, say. This works OK in some cases where callbacks are used, but
18 does require the external code to know about stable pointers and how to deal
19 with them. We'd like to hide the Haskell-nature of a callback and have it
20 be invoked just like any other C function pointer.
22 Enter adjustor thunks. An adjustor thunk is a little piece of code
23 that's generated on-the-fly (one per Haskell closure being exported)
24 that, when entered using some 'universal' calling convention (e.g., the
25 C calling convention on platform X), pushes an implicit stable pointer
26 (to the Haskell callback) before calling another (static) C function stub
27 which takes care of entering the Haskell code via its stable pointer.
29 An adjustor thunk is allocated on the C heap, and is called from within
30 Haskell just before handing out the function pointer to the Haskell (IO)
31 action. User code should never have to invoke it explicitly.
33 An adjustor thunk differs from a C function pointer in one respect: when
34 the code is through with it, it has to be freed in order to release Haskell
35 and C resources. Failure to do so result in memory leaks on both the C and
39 #include "PosixSource.h"
41 #include "RtsExternal.h"
49 /* Heavily arch-specific, I'm afraid.. */
57 * Function: execPage()
59 * Set the executable bit on page containing addr.
61 * TODO: Can the code span more than one page? If yes, we need to make two
65 execPage (void* addr, pageMode mode)
67 #if defined(i386_TARGET_ARCH) && defined(_WIN32) && 0
69 DWORD dwOldProtect = 0;
71 /* doesn't return a result, so presumably it can't fail... */
72 GetSystemInfo(&sInfo);
74 if ( VirtualProtect ( (void*)((unsigned long)addr & (sInfo.dwPageSize - 1)),
76 ( mode == pageExecuteReadWrite ? PAGE_EXECUTE_READWRITE : PAGE_EXECUTE_READ),
77 &dwOldProtect) == 0 ) {
79 DWORD rc = GetLastError();
80 prog_belch("execPage: failed to protect 0x%p; error=%lu; old protection: %lu\n", addr, rc, dwOldProtect);
86 (void)addr; (void)mode; /* keep gcc -Wall happy */
91 #if defined(i386_TARGET_ARCH)
92 static unsigned char *obscure_ccall_ret_code;
95 #if defined(alpha_TARGET_ARCH)
96 /* To get the definition of PAL_imb: */
97 # if defined(linux_TARGET_OS)
100 # include <machine/pal.h>
104 #if defined(ia64_TARGET_ARCH)
107 /* Layout of a function descriptor */
108 typedef struct _IA64FunDesc {
114 stgAllocStable(size_t size_in_bytes, StgStablePtr *stable)
117 nat data_size_in_words, total_size_in_words;
119 /* round up to a whole number of words */
120 data_size_in_words = (size_in_bytes + sizeof(W_) + 1) / sizeof(W_);
121 total_size_in_words = sizeofW(StgArrWords) + data_size_in_words;
123 /* allocate and fill it in */
124 arr = (StgArrWords *)allocate(total_size_in_words);
125 SET_ARR_HDR(arr, &stg_ARR_WORDS_info, CCCS, data_size_in_words);
127 /* obtain a stable ptr */
128 *stable = getStablePtr((StgPtr)arr);
130 /* and return a ptr to the goods inside the array */
131 return(BYTE_ARR_CTS(arr));
136 createAdjustor(int cconv, StgStablePtr hptr, StgFunPtr wptr)
138 void *adjustor = NULL;
142 case 0: /* _stdcall */
143 #if defined(i386_TARGET_ARCH)
144 /* Magic constant computed by inspecting the code length of
145 the following assembly language snippet
146 (offset and machine code prefixed):
148 <0>: 58 popl %eax # temp. remove ret addr..
149 <1>: 68 fd fc fe fa pushl 0xfafefcfd # constant is large enough to
150 # hold a StgStablePtr
151 <6>: 50 pushl %eax # put back ret. addr
152 <7>: b8 fa ef ff 00 movl $0x00ffeffa, %eax # load up wptr
153 <c>: ff e0 jmp %eax # and jump to it.
154 # the callee cleans up the stack
156 adjustor = stgMallocBytes(14, "createAdjustor");
158 unsigned char *const adj_code = (unsigned char *)adjustor;
159 adj_code[0x00] = (unsigned char)0x58; /* popl %eax */
161 adj_code[0x01] = (unsigned char)0x68; /* pushl hptr (which is a dword immediate ) */
162 *((StgStablePtr*)(adj_code + 0x02)) = (StgStablePtr)hptr;
164 adj_code[0x06] = (unsigned char)0x50; /* pushl %eax */
166 adj_code[0x07] = (unsigned char)0xb8; /* movl $wptr, %eax */
167 *((StgFunPtr*)(adj_code + 0x08)) = (StgFunPtr)wptr;
169 adj_code[0x0c] = (unsigned char)0xff; /* jmp %eax */
170 adj_code[0x0d] = (unsigned char)0xe0;
172 execPage(adjustor, pageExecuteReadWrite);
178 #if defined(i386_TARGET_ARCH)
179 /* Magic constant computed by inspecting the code length of
180 the following assembly language snippet
181 (offset and machine code prefixed):
183 <00>: 68 ef be ad de pushl $0xdeadbeef # constant is large enough to
184 # hold a StgStablePtr
185 <05>: b8 fa ef ff 00 movl $0x00ffeffa, %eax # load up wptr
186 <0a>: 68 ef be ad de pushl $obscure_ccall_ret_code # push the return address
187 <0f>: ff e0 jmp *%eax # jump to wptr
189 The ccall'ing version is a tad different, passing in the return
190 address of the caller to the auto-generated C stub (which enters
191 via the stable pointer.) (The auto-generated C stub is in on this
192 game, don't worry :-)
194 See the comment next to obscure_ccall_ret_code why we need to
195 perform a tail jump instead of a call, followed by some C stack
198 Note: The adjustor makes the assumption that any return value
199 coming back from the C stub is not stored on the stack.
200 That's (thankfully) the case here with the restricted set of
201 return types that we support.
203 adjustor = stgMallocBytes(17, "createAdjustor");
205 unsigned char *const adj_code = (unsigned char *)adjustor;
207 adj_code[0x00] = (unsigned char)0x68; /* pushl hptr (which is a dword immediate ) */
208 *((StgStablePtr*)(adj_code+0x01)) = (StgStablePtr)hptr;
210 adj_code[0x05] = (unsigned char)0xb8; /* movl $wptr, %eax */
211 *((StgFunPtr*)(adj_code + 0x06)) = (StgFunPtr)wptr;
213 adj_code[0x0a] = (unsigned char)0x68; /* pushl obscure_ccall_ret_code */
214 *((StgFunPtr*)(adj_code + 0x0b)) = (StgFunPtr)obscure_ccall_ret_code;
216 adj_code[0x0f] = (unsigned char)0xff; /* jmp *%eax */
217 adj_code[0x10] = (unsigned char)0xe0;
219 execPage(adjustor, pageExecuteReadWrite);
221 #elif defined(sparc_TARGET_ARCH)
222 /* Magic constant computed by inspecting the code length of the following
223 assembly language snippet (offset and machine code prefixed):
225 <00>: 9C23A008 sub %sp, 8, %sp ! make room for %o4/%o5 in caller's frame
226 <04>: DA23A060 st %o5, [%sp + 96] ! shift registers by 2 positions
227 <08>: D823A05C st %o4, [%sp + 92]
228 <0C>: 9A10000B mov %o3, %o5
229 <10>: 9810000A mov %o2, %o4
230 <14>: 96100009 mov %o1, %o3
231 <18>: 94100008 mov %o0, %o2
232 <1C>: 13000000 sethi %hi(wptr), %o1 ! load up wptr (1 of 2)
233 <20>: 11000000 sethi %hi(hptr), %o0 ! load up hptr (1 of 2)
234 <24>: 81C26000 jmp %o1 + %lo(wptr) ! jump to wptr (load 2 of 2)
235 <28>: 90122000 or %o0, %lo(hptr), %o0 ! load up hptr (2 of 2, delay slot)
236 <2C> 00000000 ! place for getting hptr back easily
238 ccall'ing on SPARC is easy, because we are quite lucky to push a
239 multiple of 8 bytes (1 word hptr + 1 word dummy arg) in front of the
240 existing arguments (note that %sp must stay double-word aligned at
241 all times, see ABI spec at http://www.sparc.org/standards/psABI3rd.pdf).
242 To do this, we extend the *caller's* stack frame by 2 words and shift
243 the output registers used for argument passing (%o0 - %o5, we are a *leaf*
244 procedure because of the tail-jump) by 2 positions. This makes room in
245 %o0 and %o1 for the additinal arguments, namely hptr and a dummy (used
246 for destination addr of jump on SPARC, return address on x86, ...). This
247 shouldn't cause any problems for a C-like caller: alloca is implemented
248 similarly, and local variables should be accessed via %fp, not %sp. In a
249 nutshell: This should work! (Famous last words! :-)
251 adjustor = stgMallocBytes(4*(11+1), "createAdjustor");
253 unsigned long *const adj_code = (unsigned long *)adjustor;
255 adj_code[ 0] = 0x9C23A008UL; /* sub %sp, 8, %sp */
256 adj_code[ 1] = 0xDA23A060UL; /* st %o5, [%sp + 96] */
257 adj_code[ 2] = 0xD823A05CUL; /* st %o4, [%sp + 92] */
258 adj_code[ 3] = 0x9A10000BUL; /* mov %o3, %o5 */
259 adj_code[ 4] = 0x9810000AUL; /* mov %o2, %o4 */
260 adj_code[ 5] = 0x96100009UL; /* mov %o1, %o3 */
261 adj_code[ 6] = 0x94100008UL; /* mov %o0, %o2 */
262 adj_code[ 7] = 0x13000000UL; /* sethi %hi(wptr), %o1 */
263 adj_code[ 7] |= ((unsigned long)wptr) >> 10;
264 adj_code[ 8] = 0x11000000UL; /* sethi %hi(hptr), %o0 */
265 adj_code[ 8] |= ((unsigned long)hptr) >> 10;
266 adj_code[ 9] = 0x81C26000UL; /* jmp %o1 + %lo(wptr) */
267 adj_code[ 9] |= ((unsigned long)wptr) & 0x000003FFUL;
268 adj_code[10] = 0x90122000UL; /* or %o0, %lo(hptr), %o0 */
269 adj_code[10] |= ((unsigned long)hptr) & 0x000003FFUL;
271 adj_code[11] = (unsigned long)hptr;
274 asm("flush %0" : : "r" (adj_code ));
275 asm("flush %0" : : "r" (adj_code + 2));
276 asm("flush %0" : : "r" (adj_code + 4));
277 asm("flush %0" : : "r" (adj_code + 6));
278 asm("flush %0" : : "r" (adj_code + 10));
280 /* max. 5 instructions latency, and we need at >= 1 for returning */
286 #elif defined(alpha_TARGET_ARCH)
287 /* Magic constant computed by inspecting the code length of
288 the following assembly language snippet
289 (offset and machine code prefixed; note that the machine code
290 shown is longwords stored in little-endian order):
292 <00>: 46520414 mov a2, a4
293 <04>: 46100412 mov a0, a2
294 <08>: a61b0020 ldq a0, 0x20(pv) # load up hptr
295 <0c>: 46730415 mov a3, a5
296 <10>: a77b0028 ldq pv, 0x28(pv) # load up wptr
297 <14>: 46310413 mov a1, a3
298 <18>: 6bfb---- jmp (pv), <hint> # jump to wptr (with hint)
299 <1c>: 00000000 # padding for alignment
300 <20>: [8 bytes for hptr quadword]
301 <28>: [8 bytes for wptr quadword]
303 The "computed" jump at <08> above is really a jump to a fixed
304 location. Accordingly, we place an always-correct hint in the
305 jump instruction, namely the address offset from <0c> to wptr,
306 divided by 4, taking the lowest 14 bits.
308 We only support passing 4 or fewer argument words, for the same
309 reason described under sparc_TARGET_ARCH above by JRS, 21 Aug 01.
310 On the Alpha the first 6 integer arguments are in a0 through a5,
311 and the rest on the stack. Hence we want to shuffle the original
312 caller's arguments by two.
314 On the Alpha the calling convention is so complex and dependent
315 on the callee's signature -- for example, the stack pointer has
316 to be a multiple of 16 -- that it seems impossible to me [ccshan]
317 to handle the general case correctly without changing how the
318 adjustor is called from C. For now, our solution of shuffling
319 registers only and ignoring the stack only works if the original
320 caller passed 4 or fewer argument words.
322 TODO: Depending on how much allocation overhead stgMallocBytes uses for
323 header information (more precisely, if the overhead is no more than
324 4 bytes), we should move the first three instructions above down by
325 4 bytes (getting rid of the nop), hence saving memory. [ccshan]
327 ASSERT(((StgWord64)wptr & 3) == 0);
328 adjustor = stgMallocBytes(48, "createAdjustor");
330 StgWord64 *const code = (StgWord64 *)adjustor;
332 code[0] = 0x4610041246520414L;
333 code[1] = 0x46730415a61b0020L;
334 code[2] = 0x46310413a77b0028L;
335 code[3] = 0x000000006bfb0000L
336 | (((StgWord32*)(wptr) - (StgWord32*)(code) - 3) & 0x3fff);
338 code[4] = (StgWord64)hptr;
339 code[5] = (StgWord64)wptr;
341 /* Ensure that instruction cache is consistent with our new code */
342 __asm__ volatile("call_pal %0" : : "i" (PAL_imb));
344 #elif defined(powerpc_TARGET_ARCH)
346 For PowerPC, the following code is used:
354 lis r0,0xDEAD ;hi(wptr)
355 lis r3,0xDEAF ;hi(hptr)
356 ori r0,r0,0xBEEF ; lo(wptr)
357 ori r3,r3,0xFACE ; lo(hptr)
361 The arguments (passed in registers r3 - r10) are shuffled along by two to
362 make room for hptr and a dummy argument. As r9 and r10 are overwritten by
363 this code, it only works for up to 6 arguments (when floating point arguments
364 are involved, this may be more or less, depending on the exact situation).
366 adjustor = stgMallocBytes(4*13, "createAdjustor");
368 unsigned long *const adj_code = (unsigned long *)adjustor;
370 // make room for extra arguments
371 adj_code[0] = 0x7d0a4378; //mr r10,r8
372 adj_code[1] = 0x7ce93b78; //mr r9,r7
373 adj_code[2] = 0x7cc83378; //mr r8,r6
374 adj_code[3] = 0x7ca72b78; //mr r7,r5
375 adj_code[4] = 0x7c862378; //mr r6,r4
376 adj_code[5] = 0x7c651b78; //mr r5,r3
378 adj_code[6] = 0x3c000000; //lis r0,hi(wptr)
379 adj_code[6] |= ((unsigned long)wptr) >> 16;
381 adj_code[7] = 0x3c600000; //lis r3,hi(hptr)
382 adj_code[7] |= ((unsigned long)hptr) >> 16;
384 adj_code[8] = 0x60000000; //ori r0,r0,lo(wptr)
385 adj_code[8] |= ((unsigned long)wptr) & 0xFFFF;
387 adj_code[9] = 0x60630000; //ori r3,r3,lo(hptr)
388 adj_code[9] |= ((unsigned long)hptr) & 0xFFFF;
390 adj_code[10] = 0x7c0903a6; //mtctr r0
391 adj_code[11] = 0x4e800420; //bctr
392 adj_code[12] = (unsigned long)hptr;
394 // Flush the Instruction cache:
395 // MakeDataExecutable(adjustor,4*13);
396 /* This would require us to link with CoreServices.framework */
397 { /* this should do the same: */
399 unsigned long *p = adj_code;
402 __asm__ volatile ("dcbf 0,%0\n\tsync\n\ticbi 0,%0"
406 __asm__ volatile ("sync\n\tisync");
409 #elif defined(ia64_TARGET_ARCH)
411 Up to 8 inputs are passed in registers. We flush the last two inputs to
412 the stack, initially into the 16-byte scratch region left by the caller.
413 We then shuffle the others along by 4 (taking 2 registers for ourselves
414 to save return address and previous function state - we need to come back
415 here on the way out to restore the stack, so this is a real function
416 rather than just a trampoline).
418 The function descriptor we create contains the gp of the target function
419 so gp is already loaded correctly.
421 [MLX] alloc r16=ar.pfs,10,2,0
423 [MII] st8.spill [r12]=r38,8 // spill in6 (out4)
424 mov r41=r37 // out7 = in5 (out3)
425 mov r40=r36;; // out6 = in4 (out2)
426 [MII] st8.spill [r12]=r39 // spill in7 (out5)
428 mov r38=r34;; // out4 = in2 (out0)
429 [MII] mov r39=r35 // out5 = in3 (out1)
430 mov r37=r33 // out3 = in1 (loc1)
431 mov r36=r32 // out2 = in0 (loc0)
432 [MLX] adds r12=-24,r12 // update sp
433 movl r34=hptr;; // out0 = hptr
434 [MIB] mov r33=r16 // loc1 = ar.pfs
435 mov r32=b0 // loc0 = retaddr
436 br.call.sptk.many b0=b6;;
438 [MII] adds r12=-16,r12
443 br.ret.sptk.many b0;;
446 /* These macros distribute a long constant into the two words of an MLX bundle */
447 #define BITS(val,start,count) (((val) >> (start)) & ((1 << (count))-1))
448 #define MOVL_LOWORD(val) (BITS(val,22,18) << 46)
449 #define MOVL_HIWORD(val) (BITS(val,40,23) | (BITS(val,0,7) << 36) | (BITS(val,7,9) << 50) \
450 | (BITS(val,16,5) << 55) | (BITS(val,21,1) << 44) | BITS(val,63,1) << 59)
454 IA64FunDesc *wdesc = (IA64FunDesc *)wptr;
455 StgWord64 wcode = wdesc->ip;
459 /* we allocate on the Haskell heap since malloc'd memory isn't executable - argh */
460 adjustor = stgAllocStable(sizeof(IA64FunDesc)+18*8, &stable);
462 fdesc = (IA64FunDesc *)adjustor;
463 code = (StgWord64 *)(fdesc + 1);
464 fdesc->ip = (StgWord64)code;
465 fdesc->gp = wdesc->gp;
467 code[0] = 0x0000058004288004 | MOVL_LOWORD(wcode);
468 code[1] = 0x6000000220000000 | MOVL_HIWORD(wcode);
469 code[2] = 0x029015d818984001;
470 code[3] = 0x8401200500420094;
471 code[4] = 0x886011d8189c0001;
472 code[5] = 0x84011004c00380c0;
473 code[6] = 0x0250210046013800;
474 code[7] = 0x8401000480420084;
475 code[8] = 0x0000233f19a06005 | MOVL_LOWORD((StgWord64)hptr);
476 code[9] = 0x6000000440000000 | MOVL_HIWORD((StgWord64)hptr);
477 code[10] = 0x0200210020010811;
478 code[11] = 0x1080006800006200;
479 code[12] = 0x0000210018406000;
480 code[13] = 0x00aa021000038005;
481 code[14] = 0x000000010000001d;
482 code[15] = 0x0084000880000200;
484 /* save stable pointers in convenient form */
485 code[16] = (StgWord64)hptr;
486 code[17] = (StgWord64)stable;
489 barf("adjustor creation not supported on this platform");
504 freeHaskellFunctionPtr(void* ptr)
506 #if defined(i386_TARGET_ARCH)
507 if ( *(unsigned char*)ptr != 0x68 &&
508 *(unsigned char*)ptr != 0x58 ) {
509 prog_belch("freeHaskellFunctionPtr: not for me, guv! %p\n", ptr);
513 /* Free the stable pointer first..*/
514 if (*(unsigned char*)ptr == 0x68) { /* Aha, a ccall adjustor! */
515 freeStablePtr(*((StgStablePtr*)((unsigned char*)ptr + 0x01)));
517 freeStablePtr(*((StgStablePtr*)((unsigned char*)ptr + 0x02)));
519 #elif defined(sparc_TARGET_ARCH)
520 if ( *(unsigned long*)ptr != 0x9C23A008UL ) {
521 prog_belch("freeHaskellFunctionPtr: not for me, guv! %p\n", ptr);
525 /* Free the stable pointer first..*/
526 freeStablePtr(*((StgStablePtr*)((unsigned long*)ptr + 11)));
527 #elif defined(alpha_TARGET_ARCH)
528 if ( *(StgWord64*)ptr != 0xa77b0018a61b0010L ) {
529 prog_belch("freeHaskellFunctionPtr: not for me, guv! %p\n", ptr);
533 /* Free the stable pointer first..*/
534 freeStablePtr(*((StgStablePtr*)((unsigned char*)ptr + 0x10)));
535 #elif defined(powerpc_TARGET_ARCH)
536 if ( *(StgWord*)ptr != 0x7d0a4378 ) {
537 prog_belch("freeHaskellFunctionPtr: not for me, guv! %p\n", ptr);
540 freeStablePtr(*((StgStablePtr*)((unsigned char*)ptr + 4*12)));
541 #elif defined(ia64_TARGET_ARCH)
542 IA64FunDesc *fdesc = (IA64FunDesc *)ptr;
543 StgWord64 *code = (StgWord64 *)(fdesc+1);
545 if (fdesc->ip != (StgWord64)code) {
546 prog_belch("freeHaskellFunctionPtr: not for me, guv! %p\n", ptr);
549 freeStablePtr((StgStablePtr)code[16]);
550 freeStablePtr((StgStablePtr)code[17]);
555 *((unsigned char*)ptr) = '\0';
562 * Function: initAdjustor()
564 * Perform initialisation of adjustor thunk layer (if needed.)
569 #if defined(i386_TARGET_ARCH)
570 /* Now here's something obscure for you:
572 When generating an adjustor thunk that uses the C calling
573 convention, we have to make sure that the thunk kicks off
574 the process of jumping into Haskell with a tail jump. Why?
575 Because as a result of jumping in into Haskell we may end
576 up freeing the very adjustor thunk we came from using
577 freeHaskellFunctionPtr(). Hence, we better not return to
578 the adjustor code on our way out, since it could by then
581 The fix is readily at hand, just include the opcodes
582 for the C stack fixup code that we need to perform when
583 returning in some static piece of memory and arrange
584 to return to it before tail jumping from the adjustor thunk.
587 obscure_ccall_ret_code = stgMallocBytes(4, "initAdjustor");
589 obscure_ccall_ret_code[0x00] = (unsigned char)0x83; /* addl $0x4, %esp */
590 obscure_ccall_ret_code[0x01] = (unsigned char)0xc4;
591 obscure_ccall_ret_code[0x02] = (unsigned char)0x04;
593 obscure_ccall_ret_code[0x03] = (unsigned char)0xc3; /* ret */
595 execPage(obscure_ccall_ret_code, pageExecuteRead);