arch/mips/kernel/unaligned.c

   1 /*
   2  * Handle unaligned accesses by emulation.
   3  *
   4  * This file is subject to the terms and conditions of the GNU General Public
   5  * License.  See the file "COPYING" in the main directory of this archive
   6  * for more details.
   7  *
   8  * Copyright (C) 1996, 1998, 1999, 2002 by Ralf Baechle
   9  * Copyright (C) 1999 Silicon Graphics, Inc.
  10  *
  11  * This file contains exception handler for address error exception with the
  12  * special capability to execute faulting instructions in software.  The
  13  * handler does not try to handle the case when the program counter points
  14  * to an address not aligned to a word boundary.
  15  *
  16  * Putting data to unaligned addresses is a bad practice even on Intel where
  17  * only the performance is affected.  Much worse is that such code is non-
  18  * portable.  Due to several programs that die on MIPS due to alignment
  19  * problems I decided to implement this handler anyway though I originally
  20  * didn't intend to do this at all for user code.
  21  *
  22  * For now I enable fixing of address errors by default to make life easier.
  23  * I however intend to disable this somewhen in the future when the alignment
  24  * problems with user programs have been fixed.  For programmers this is the
  25  * right way to go.
  26  *
  27  * Fixing address errors is a per process option.  The option is inherited
  28  * across fork(2) and execve(2) calls.  If you really want to use the
  29  * option in your user programs - I discourage the use of the software
  30  * emulation strongly - use the following code in your userland stuff:
  31  *
  32  * #include <sys/sysmips.h>
  33  *
  34  * ...
  35  * sysmips(MIPS_FIXADE, x);
  36  * ...
  37  *
  38  * The argument x is 0 for disabling software emulation, enabled otherwise.
  39  *
  40  * Below a little program to play around with this feature.
  41  *
  42  * #include <stdio.h>
  43  * #include <sys/sysmips.h>
  44  *
  45  * struct foo {
  46  *         unsigned char bar[8];
  47  * };
  48  *
  49  * main(int argc, char *argv[])
  50  * {
  51  *         struct foo x = {0, 1, 2, 3, 4, 5, 6, 7};
  52  *         unsigned int *p = (unsigned int *) (x.bar + 3);
  53  *         int i;
  54  *
  55  *         if (argc > 1)
  56  *                 sysmips(MIPS_FIXADE, atoi(argv[1]));
  57  *
  58  *         printf("*p = %08lx\n", *p);
  59  *
  60  *         *p = 0xdeadface;
  61  *
  62  *         for(i = 0; i <= 7; i++)
  63  *         printf("%02x ", x.bar[i]);
  64  *         printf("\n");
  65  * }
  66  *
  67  * Coprocessor loads are not supported; I think this case is unimportant
  68  * in the practice.
  69  *
  70  * TODO: Handle ndc (attempted store to doubleword in uncached memory)
  71  *       exception for the R6000.
  72  *       A store crossing a page boundary might be executed only partially.
  73  *       Undo the partial store in this case.
  74  */
  75 #include <linux/mm.h>
  76 #include <linux/module.h>
  77 #include <linux/signal.h>
  78 #include <linux/smp.h>
  79 #include <linux/smp_lock.h>
  80
  81 #include <asm/asm.h>
  82 #include <asm/branch.h>
  83 #include <asm/byteorder.h>
  84 #include <asm/inst.h>
  85 #include <asm/uaccess.h>
  86 #include <asm/system.h>
  87
  88 #define STR(x)  __STR(x)
  89 #define __STR(x)  #x
  90
  91 #ifdef CONFIG_PROC_FS
  92 unsigned long unaligned_instructions;
  93 #endif
  94
  95 static inline int emulate_load_store_insn(struct pt_regs *regs,
  96         void __user *addr, unsigned int __user *pc,
  97         unsigned long **regptr, unsigned long *newvalue)
  98 {
  99         union mips_instruction insn;
 100         unsigned long value;
 101         unsigned int res;
 102
 103         regs->regs[0] = 0;
 104         *regptr=NULL;
 105
 106         /*
 107          * This load never faults.
 108          */
 109         __get_user(insn.word, pc);
 110
 111         switch (insn.i_format.opcode) {
 112         /*
 113          * These are instructions that a compiler doesn't generate.  We
 114          * can assume therefore that the code is MIPS-aware and
 115          * really buggy.  Emulating these instructions would break the
 116          * semantics anyway.
 117          */
 118         case ll_op:
 119         case lld_op:
 120         case sc_op:
 121         case scd_op:
 122
 123         /*
 124          * For these instructions the only way to create an address
 125          * error is an attempted access to kernel/supervisor address
 126          * space.
 127          */
 128         case ldl_op:
 129         case ldr_op:
 130         case lwl_op:
 131         case lwr_op:
 132         case sdl_op:
 133         case sdr_op:
 134         case swl_op:
 135         case swr_op:
 136         case lb_op:
 137         case lbu_op:
 138         case sb_op:
 139                 goto sigbus;
 140
 141         /*
 142          * The remaining opcodes are the ones that are really of interest.
 143          */
 144         case lh_op:
 145                 if (!access_ok(VERIFY_READ, addr, 2))
 146                         goto sigbus;
 147
 148                 __asm__ __volatile__ (".set\tnoat\n"
 149 #ifdef __BIG_ENDIAN
 150                         "1:\tlb\t%0, 0(%2)\n"
 151                         "2:\tlbu\t$1, 1(%2)\n\t"
 152 #endif
 153 #ifdef __LITTLE_ENDIAN
 154                         "1:\tlb\t%0, 1(%2)\n"
 155                         "2:\tlbu\t$1, 0(%2)\n\t"
 156 #endif
 157                         "sll\t%0, 0x8\n\t"
 158                         "or\t%0, $1\n\t"
 159                         "li\t%1, 0\n"
 160                         "3:\t.set\tat\n\t"
 161                         ".section\t.fixup,\"ax\"\n\t"
 162                         "4:\tli\t%1, %3\n\t"
 163                         "j\t3b\n\t"
 164                         ".previous\n\t"
 165                         ".section\t__ex_table,\"a\"\n\t"
 166                         STR(PTR)"\t1b, 4b\n\t"
 167                         STR(PTR)"\t2b, 4b\n\t"
 168                         ".previous"
 169                         : "=&r" (value), "=r" (res)
 170                         : "r" (addr), "i" (-EFAULT));
 171                 if (res)
 172                         goto fault;
 173                 *newvalue = value;
 174                 *regptr = &regs->regs[insn.i_format.rt];
 175                 break;
 176
 177         case lw_op:
 178                 if (!access_ok(VERIFY_READ, addr, 4))
 179                         goto sigbus;
 180
 181                 __asm__ __volatile__ (
 182 #ifdef __BIG_ENDIAN
 183                         "1:\tlwl\t%0, (%2)\n"
 184                         "2:\tlwr\t%0, 3(%2)\n\t"
 185 #endif
 186 #ifdef __LITTLE_ENDIAN
 187                         "1:\tlwl\t%0, 3(%2)\n"
 188                         "2:\tlwr\t%0, (%2)\n\t"
 189 #endif
 190                         "li\t%1, 0\n"
 191                         "3:\t.section\t.fixup,\"ax\"\n\t"
 192                         "4:\tli\t%1, %3\n\t"
 193                         "j\t3b\n\t"
 194                         ".previous\n\t"
 195                         ".section\t__ex_table,\"a\"\n\t"
 196                         STR(PTR)"\t1b, 4b\n\t"
 197                         STR(PTR)"\t2b, 4b\n\t"
 198                         ".previous"
 199                         : "=&r" (value), "=r" (res)
 200                         : "r" (addr), "i" (-EFAULT));
 201                 if (res)
 202                         goto fault;
 203                 *newvalue = value;
 204                 *regptr = &regs->regs[insn.i_format.rt];
 205                 break;
 206
 207         case lhu_op:
 208                 if (!access_ok(VERIFY_READ, addr, 2))
 209                         goto sigbus;
 210
 211                 __asm__ __volatile__ (
 212                         ".set\tnoat\n"
 213 #ifdef __BIG_ENDIAN
 214                         "1:\tlbu\t%0, 0(%2)\n"
 215                         "2:\tlbu\t$1, 1(%2)\n\t"
 216 #endif
 217 #ifdef __LITTLE_ENDIAN
 218                         "1:\tlbu\t%0, 1(%2)\n"
 219                         "2:\tlbu\t$1, 0(%2)\n\t"
 220 #endif
 221                         "sll\t%0, 0x8\n\t"
 222                         "or\t%0, $1\n\t"
 223                         "li\t%1, 0\n"
 224                         "3:\t.set\tat\n\t"
 225                         ".section\t.fixup,\"ax\"\n\t"
 226                         "4:\tli\t%1, %3\n\t"
 227                         "j\t3b\n\t"
 228                         ".previous\n\t"
 229                         ".section\t__ex_table,\"a\"\n\t"
 230                         STR(PTR)"\t1b, 4b\n\t"
 231                         STR(PTR)"\t2b, 4b\n\t"
 232                         ".previous"
 233                         : "=&r" (value), "=r" (res)
 234                         : "r" (addr), "i" (-EFAULT));
 235                 if (res)
 236                         goto fault;
 237                 *newvalue = value;
 238                 *regptr = &regs->regs[insn.i_format.rt];
 239                 break;
 240
 241         case lwu_op:
 242 #ifdef CONFIG_64BIT
 243                 /*
 244                  * A 32-bit kernel might be running on a 64-bit processor.  But
 245                  * if we're on a 32-bit processor and an i-cache incoherency
 246                  * or race makes us see a 64-bit instruction here the sdl/sdr
 247                  * would blow up, so for now we don't handle unaligned 64-bit
 248                  * instructions on 32-bit kernels.
 249                  */
 250                 if (!access_ok(VERIFY_READ, addr, 4))
 251                         goto sigbus;
 252
 253                 __asm__ __volatile__ (
 254 #ifdef __BIG_ENDIAN
 255                         "1:\tlwl\t%0, (%2)\n"
 256                         "2:\tlwr\t%0, 3(%2)\n\t"
 257 #endif
 258 #ifdef __LITTLE_ENDIAN
 259                         "1:\tlwl\t%0, 3(%2)\n"
 260                         "2:\tlwr\t%0, (%2)\n\t"
 261 #endif
 262                         "dsll\t%0, %0, 32\n\t"
 263                         "dsrl\t%0, %0, 32\n\t"
 264                         "li\t%1, 0\n"
 265                         "3:\t.section\t.fixup,\"ax\"\n\t"
 266                         "4:\tli\t%1, %3\n\t"
 267                         "j\t3b\n\t"
 268                         ".previous\n\t"
 269                         ".section\t__ex_table,\"a\"\n\t"
 270                         STR(PTR)"\t1b, 4b\n\t"
 271                         STR(PTR)"\t2b, 4b\n\t"
 272                         ".previous"
 273                         : "=&r" (value), "=r" (res)
 274                         : "r" (addr), "i" (-EFAULT));
 275                 if (res)
 276                         goto fault;
 277                 *newvalue = value;
 278                 *regptr = &regs->regs[insn.i_format.rt];
 279                 break;
 280 #endif /* CONFIG_64BIT */
 281
 282                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 283                 goto sigill;
 284
 285         case ld_op:
 286 #ifdef CONFIG_64BIT
 287                 /*
 288                  * A 32-bit kernel might be running on a 64-bit processor.  But
 289                  * if we're on a 32-bit processor and an i-cache incoherency
 290                  * or race makes us see a 64-bit instruction here the sdl/sdr
 291                  * would blow up, so for now we don't handle unaligned 64-bit
 292                  * instructions on 32-bit kernels.
 293                  */
 294                 if (!access_ok(VERIFY_READ, addr, 8))
 295                         goto sigbus;
 296
 297                 __asm__ __volatile__ (
 298 #ifdef __BIG_ENDIAN
 299                         "1:\tldl\t%0, (%2)\n"
 300                         "2:\tldr\t%0, 7(%2)\n\t"
 301 #endif
 302 #ifdef __LITTLE_ENDIAN
 303                         "1:\tldl\t%0, 7(%2)\n"
 304                         "2:\tldr\t%0, (%2)\n\t"
 305 #endif
 306                         "li\t%1, 0\n"
 307                         "3:\t.section\t.fixup,\"ax\"\n\t"
 308                         "4:\tli\t%1, %3\n\t"
 309                         "j\t3b\n\t"
 310                         ".previous\n\t"
 311                         ".section\t__ex_table,\"a\"\n\t"
 312                         STR(PTR)"\t1b, 4b\n\t"
 313                         STR(PTR)"\t2b, 4b\n\t"
 314                         ".previous"
 315                         : "=&r" (value), "=r" (res)
 316                         : "r" (addr), "i" (-EFAULT));
 317                 if (res)
 318                         goto fault;
 319                 *newvalue = value;
 320                 *regptr = &regs->regs[insn.i_format.rt];
 321                 break;
 322 #endif /* CONFIG_64BIT */
 323
 324                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 325                 goto sigill;
 326
 327         case sh_op:
 328                 if (!access_ok(VERIFY_WRITE, addr, 2))
 329                         goto sigbus;
 330
 331                 value = regs->regs[insn.i_format.rt];
 332                 __asm__ __volatile__ (
 333 #ifdef __BIG_ENDIAN
 334                         ".set\tnoat\n"
 335                         "1:\tsb\t%1, 1(%2)\n\t"
 336                         "srl\t$1, %1, 0x8\n"
 337                         "2:\tsb\t$1, 0(%2)\n\t"
 338                         ".set\tat\n\t"
 339 #endif
 340 #ifdef __LITTLE_ENDIAN
 341                         ".set\tnoat\n"
 342                         "1:\tsb\t%1, 0(%2)\n\t"
 343                         "srl\t$1,%1, 0x8\n"
 344                         "2:\tsb\t$1, 1(%2)\n\t"
 345                         ".set\tat\n\t"
 346 #endif
 347                         "li\t%0, 0\n"
 348                         "3:\n\t"
 349                         ".section\t.fixup,\"ax\"\n\t"
 350                         "4:\tli\t%0, %3\n\t"
 351                         "j\t3b\n\t"
 352                         ".previous\n\t"
 353                         ".section\t__ex_table,\"a\"\n\t"
 354                         STR(PTR)"\t1b, 4b\n\t"
 355                         STR(PTR)"\t2b, 4b\n\t"
 356                         ".previous"
 357                         : "=r" (res)
 358                         : "r" (value), "r" (addr), "i" (-EFAULT));
 359                 if (res)
 360                         goto fault;
 361                 break;
 362
 363         case sw_op:
 364                 if (!access_ok(VERIFY_WRITE, addr, 4))
 365                         goto sigbus;
 366
 367                 value = regs->regs[insn.i_format.rt];
 368                 __asm__ __volatile__ (
 369 #ifdef __BIG_ENDIAN
 370                         "1:\tswl\t%1,(%2)\n"
 371                         "2:\tswr\t%1, 3(%2)\n\t"
 372 #endif
 373 #ifdef __LITTLE_ENDIAN
 374                         "1:\tswl\t%1, 3(%2)\n"
 375                         "2:\tswr\t%1, (%2)\n\t"
 376 #endif
 377                         "li\t%0, 0\n"
 378                         "3:\n\t"
 379                         ".section\t.fixup,\"ax\"\n\t"
 380                         "4:\tli\t%0, %3\n\t"
 381                         "j\t3b\n\t"
 382                         ".previous\n\t"
 383                         ".section\t__ex_table,\"a\"\n\t"
 384                         STR(PTR)"\t1b, 4b\n\t"
 385                         STR(PTR)"\t2b, 4b\n\t"
 386                         ".previous"
 387                 : "=r" (res)
 388                 : "r" (value), "r" (addr), "i" (-EFAULT));
 389                 if (res)
 390                         goto fault;
 391                 break;
 392
 393         case sd_op:
 394 #ifdef CONFIG_64BIT
 395                 /*
 396                  * A 32-bit kernel might be running on a 64-bit processor.  But
 397                  * if we're on a 32-bit processor and an i-cache incoherency
 398                  * or race makes us see a 64-bit instruction here the sdl/sdr
 399                  * would blow up, so for now we don't handle unaligned 64-bit
 400                  * instructions on 32-bit kernels.
 401                  */
 402                 if (!access_ok(VERIFY_WRITE, addr, 8))
 403                         goto sigbus;
 404
 405                 value = regs->regs[insn.i_format.rt];
 406                 __asm__ __volatile__ (
 407 #ifdef __BIG_ENDIAN
 408                         "1:\tsdl\t%1,(%2)\n"
 409                         "2:\tsdr\t%1, 7(%2)\n\t"
 410 #endif
 411 #ifdef __LITTLE_ENDIAN
 412                         "1:\tsdl\t%1, 7(%2)\n"
 413                         "2:\tsdr\t%1, (%2)\n\t"
 414 #endif
 415                         "li\t%0, 0\n"
 416                         "3:\n\t"
 417                         ".section\t.fixup,\"ax\"\n\t"
 418                         "4:\tli\t%0, %3\n\t"
 419                         "j\t3b\n\t"
 420                         ".previous\n\t"
 421                         ".section\t__ex_table,\"a\"\n\t"
 422                         STR(PTR)"\t1b, 4b\n\t"
 423                         STR(PTR)"\t2b, 4b\n\t"
 424                         ".previous"
 425                 : "=r" (res)
 426                 : "r" (value), "r" (addr), "i" (-EFAULT));
 427                 if (res)
 428                         goto fault;
 429                 break;
 430 #endif /* CONFIG_64BIT */
 431
 432                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 433                 goto sigill;
 434
 435         case lwc1_op:
 436         case ldc1_op:
 437         case swc1_op:
 438         case sdc1_op:
 439                 /*
 440                  * I herewith declare: this does not happen.  So send SIGBUS.
 441                  */
 442                 goto sigbus;
 443
 444         case lwc2_op:
 445         case ldc2_op:
 446         case swc2_op:
 447         case sdc2_op:
 448                 /*
 449                  * These are the coprocessor 2 load/stores.  The current
 450                  * implementations don't use cp2 and cp2 should always be
 451                  * disabled in c0_status.  So send SIGILL.
 452                  * (No longer true: The Sony Praystation uses cp2 for
 453                  * 3D matrix operations.  Dunno if that thingy has a MMU ...)
 454                  */
 455         default:
 456                 /*
 457                  * Pheeee...  We encountered an yet unknown instruction or
 458                  * cache coherence problem.  Die sucker, die ...
 459                  */
 460                 goto sigill;
 461         }
 462
 463 #ifdef CONFIG_PROC_FS
 464         unaligned_instructions++;
 465 #endif
 466
 467         return 0;
 468
 469 fault:
 470         /* Did we have an exception handler installed? */
 471         if (fixup_exception(regs))
 472                 return 1;
 473
 474         die_if_kernel ("Unhandled kernel unaligned access", regs);
 475         send_sig(SIGSEGV, current, 1);
 476
 477         return 0;
 478
 479 sigbus:
 480         die_if_kernel("Unhandled kernel unaligned access", regs);
 481         send_sig(SIGBUS, current, 1);
 482
 483         return 0;
 484
 485 sigill:
 486         die_if_kernel("Unhandled kernel unaligned access or invalid instruction", regs);
 487         send_sig(SIGILL, current, 1);
 488
 489         return 0;
 490 }
 491
 492 asmlinkage void do_ade(struct pt_regs *regs)
 493 {
 494         unsigned long *regptr, newval;
 495         extern int do_dsemulret(struct pt_regs *);
 496         unsigned int __user *pc;
 497         mm_segment_t seg;
 498
 499         /*
 500          * Address errors may be deliberately induced by the FPU emulator to
 501          * retake control of the CPU after executing the instruction in the
 502          * delay slot of an emulated branch.
 503          */
 504         /* Terminate if exception was recognized as a delay slot return */
 505         if (do_dsemulret(regs))
 506                 return;
 507
 508         /* Otherwise handle as normal */
 509
 510         /*
 511          * Did we catch a fault trying to load an instruction?
 512          * Or are we running in MIPS16 mode?
 513          */
 514         if ((regs->cp0_badvaddr == regs->cp0_epc) || (regs->cp0_epc & 0x1))
 515                 goto sigbus;
 516
 517         pc = (unsigned int __user *) exception_epc(regs);
 518         if ((current->thread.mflags & MF_FIXADE) == 0)
 519                 goto sigbus;
 520
 521         /*
 522          * Do branch emulation only if we didn't forward the exception.
 523          * This is all so but ugly ...
 524          */
 525         seg = get_fs();
 526         if (!user_mode(regs))
 527                 set_fs(KERNEL_DS);
 528         if (!emulate_load_store_insn(regs, (void __user *)regs->cp0_badvaddr, pc,
 529                                      &regptr, &newval)) {
 530                 compute_return_epc(regs);
 531                 /*
 532                  * Now that branch is evaluated, update the dest
 533                  * register if necessary
 534                  */
 535                 if (regptr)
 536                         *regptr = newval;
 537         }
 538         set_fs(seg);
 539
 540         return;
 541
 542 sigbus:
 543         die_if_kernel("Kernel unaligned instruction access", regs);
 544         force_sig(SIGBUS, current);
 545
 546         /*
 547          * XXX On return from the signal handler we should advance the epc
 548          */
 549 }