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/sched.h>
  80 #include <linux/debugfs.h>
  81 #include <linux/perf_event.h>
  82
  83 #include <asm/asm.h>
  84 #include <asm/branch.h>
  85 #include <asm/byteorder.h>
  86 #include <asm/cop2.h>
  87 #include <asm/inst.h>
  88 #include <asm/uaccess.h>
  89 #include <asm/system.h>
  90
  91 #define STR(x)  __STR(x)
  92 #define __STR(x)  #x
  93
  94 enum {
  95         UNALIGNED_ACTION_QUIET,
  96         UNALIGNED_ACTION_SIGNAL,
  97         UNALIGNED_ACTION_SHOW,
  98 };
  99 #ifdef CONFIG_DEBUG_FS
 100 static u32 unaligned_instructions;
 101 static u32 unaligned_action;
 102 #else
 103 #define unaligned_action UNALIGNED_ACTION_QUIET
 104 #endif
 105 extern void show_registers(struct pt_regs *regs);
 106
 107 static void emulate_load_store_insn(struct pt_regs *regs,
 108         void __user *addr, unsigned int __user *pc)
 109 {
 110         union mips_instruction insn;
 111         unsigned long value;
 112         unsigned int res;
 113
 114         perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS,
 115                       1, 0, regs, 0);
 116
 117         /*
 118          * This load never faults.
 119          */
 120         __get_user(insn.word, pc);
 121
 122         switch (insn.i_format.opcode) {
 123         /*
 124          * These are instructions that a compiler doesn't generate.  We
 125          * can assume therefore that the code is MIPS-aware and
 126          * really buggy.  Emulating these instructions would break the
 127          * semantics anyway.
 128          */
 129         case ll_op:
 130         case lld_op:
 131         case sc_op:
 132         case scd_op:
 133
 134         /*
 135          * For these instructions the only way to create an address
 136          * error is an attempted access to kernel/supervisor address
 137          * space.
 138          */
 139         case ldl_op:
 140         case ldr_op:
 141         case lwl_op:
 142         case lwr_op:
 143         case sdl_op:
 144         case sdr_op:
 145         case swl_op:
 146         case swr_op:
 147         case lb_op:
 148         case lbu_op:
 149         case sb_op:
 150                 goto sigbus;
 151
 152         /*
 153          * The remaining opcodes are the ones that are really of interest.
 154          */
 155         case lh_op:
 156                 if (!access_ok(VERIFY_READ, addr, 2))
 157                         goto sigbus;
 158
 159                 __asm__ __volatile__ (".set\tnoat\n"
 160 #ifdef __BIG_ENDIAN
 161                         "1:\tlb\t%0, 0(%2)\n"
 162                         "2:\tlbu\t$1, 1(%2)\n\t"
 163 #endif
 164 #ifdef __LITTLE_ENDIAN
 165                         "1:\tlb\t%0, 1(%2)\n"
 166                         "2:\tlbu\t$1, 0(%2)\n\t"
 167 #endif
 168                         "sll\t%0, 0x8\n\t"
 169                         "or\t%0, $1\n\t"
 170                         "li\t%1, 0\n"
 171                         "3:\t.set\tat\n\t"
 172                         ".section\t.fixup,\"ax\"\n\t"
 173                         "4:\tli\t%1, %3\n\t"
 174                         "j\t3b\n\t"
 175                         ".previous\n\t"
 176                         ".section\t__ex_table,\"a\"\n\t"
 177                         STR(PTR)"\t1b, 4b\n\t"
 178                         STR(PTR)"\t2b, 4b\n\t"
 179                         ".previous"
 180                         : "=&r" (value), "=r" (res)
 181                         : "r" (addr), "i" (-EFAULT));
 182                 if (res)
 183                         goto fault;
 184                 compute_return_epc(regs);
 185                 regs->regs[insn.i_format.rt] = value;
 186                 break;
 187
 188         case lw_op:
 189                 if (!access_ok(VERIFY_READ, addr, 4))
 190                         goto sigbus;
 191
 192                 __asm__ __volatile__ (
 193 #ifdef __BIG_ENDIAN
 194                         "1:\tlwl\t%0, (%2)\n"
 195                         "2:\tlwr\t%0, 3(%2)\n\t"
 196 #endif
 197 #ifdef __LITTLE_ENDIAN
 198                         "1:\tlwl\t%0, 3(%2)\n"
 199                         "2:\tlwr\t%0, (%2)\n\t"
 200 #endif
 201                         "li\t%1, 0\n"
 202                         "3:\t.section\t.fixup,\"ax\"\n\t"
 203                         "4:\tli\t%1, %3\n\t"
 204                         "j\t3b\n\t"
 205                         ".previous\n\t"
 206                         ".section\t__ex_table,\"a\"\n\t"
 207                         STR(PTR)"\t1b, 4b\n\t"
 208                         STR(PTR)"\t2b, 4b\n\t"
 209                         ".previous"
 210                         : "=&r" (value), "=r" (res)
 211                         : "r" (addr), "i" (-EFAULT));
 212                 if (res)
 213                         goto fault;
 214                 compute_return_epc(regs);
 215                 regs->regs[insn.i_format.rt] = value;
 216                 break;
 217
 218         case lhu_op:
 219                 if (!access_ok(VERIFY_READ, addr, 2))
 220                         goto sigbus;
 221
 222                 __asm__ __volatile__ (
 223                         ".set\tnoat\n"
 224 #ifdef __BIG_ENDIAN
 225                         "1:\tlbu\t%0, 0(%2)\n"
 226                         "2:\tlbu\t$1, 1(%2)\n\t"
 227 #endif
 228 #ifdef __LITTLE_ENDIAN
 229                         "1:\tlbu\t%0, 1(%2)\n"
 230                         "2:\tlbu\t$1, 0(%2)\n\t"
 231 #endif
 232                         "sll\t%0, 0x8\n\t"
 233                         "or\t%0, $1\n\t"
 234                         "li\t%1, 0\n"
 235                         "3:\t.set\tat\n\t"
 236                         ".section\t.fixup,\"ax\"\n\t"
 237                         "4:\tli\t%1, %3\n\t"
 238                         "j\t3b\n\t"
 239                         ".previous\n\t"
 240                         ".section\t__ex_table,\"a\"\n\t"
 241                         STR(PTR)"\t1b, 4b\n\t"
 242                         STR(PTR)"\t2b, 4b\n\t"
 243                         ".previous"
 244                         : "=&r" (value), "=r" (res)
 245                         : "r" (addr), "i" (-EFAULT));
 246                 if (res)
 247                         goto fault;
 248                 compute_return_epc(regs);
 249                 regs->regs[insn.i_format.rt] = value;
 250                 break;
 251
 252         case lwu_op:
 253 #ifdef CONFIG_64BIT
 254                 /*
 255                  * A 32-bit kernel might be running on a 64-bit processor.  But
 256                  * if we're on a 32-bit processor and an i-cache incoherency
 257                  * or race makes us see a 64-bit instruction here the sdl/sdr
 258                  * would blow up, so for now we don't handle unaligned 64-bit
 259                  * instructions on 32-bit kernels.
 260                  */
 261                 if (!access_ok(VERIFY_READ, addr, 4))
 262                         goto sigbus;
 263
 264                 __asm__ __volatile__ (
 265 #ifdef __BIG_ENDIAN
 266                         "1:\tlwl\t%0, (%2)\n"
 267                         "2:\tlwr\t%0, 3(%2)\n\t"
 268 #endif
 269 #ifdef __LITTLE_ENDIAN
 270                         "1:\tlwl\t%0, 3(%2)\n"
 271                         "2:\tlwr\t%0, (%2)\n\t"
 272 #endif
 273                         "dsll\t%0, %0, 32\n\t"
 274                         "dsrl\t%0, %0, 32\n\t"
 275                         "li\t%1, 0\n"
 276                         "3:\t.section\t.fixup,\"ax\"\n\t"
 277                         "4:\tli\t%1, %3\n\t"
 278                         "j\t3b\n\t"
 279                         ".previous\n\t"
 280                         ".section\t__ex_table,\"a\"\n\t"
 281                         STR(PTR)"\t1b, 4b\n\t"
 282                         STR(PTR)"\t2b, 4b\n\t"
 283                         ".previous"
 284                         : "=&r" (value), "=r" (res)
 285                         : "r" (addr), "i" (-EFAULT));
 286                 if (res)
 287                         goto fault;
 288                 compute_return_epc(regs);
 289                 regs->regs[insn.i_format.rt] = value;
 290                 break;
 291 #endif /* CONFIG_64BIT */
 292
 293                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 294                 goto sigill;
 295
 296         case ld_op:
 297 #ifdef CONFIG_64BIT
 298                 /*
 299                  * A 32-bit kernel might be running on a 64-bit processor.  But
 300                  * if we're on a 32-bit processor and an i-cache incoherency
 301                  * or race makes us see a 64-bit instruction here the sdl/sdr
 302                  * would blow up, so for now we don't handle unaligned 64-bit
 303                  * instructions on 32-bit kernels.
 304                  */
 305                 if (!access_ok(VERIFY_READ, addr, 8))
 306                         goto sigbus;
 307
 308                 __asm__ __volatile__ (
 309 #ifdef __BIG_ENDIAN
 310                         "1:\tldl\t%0, (%2)\n"
 311                         "2:\tldr\t%0, 7(%2)\n\t"
 312 #endif
 313 #ifdef __LITTLE_ENDIAN
 314                         "1:\tldl\t%0, 7(%2)\n"
 315                         "2:\tldr\t%0, (%2)\n\t"
 316 #endif
 317                         "li\t%1, 0\n"
 318                         "3:\t.section\t.fixup,\"ax\"\n\t"
 319                         "4:\tli\t%1, %3\n\t"
 320                         "j\t3b\n\t"
 321                         ".previous\n\t"
 322                         ".section\t__ex_table,\"a\"\n\t"
 323                         STR(PTR)"\t1b, 4b\n\t"
 324                         STR(PTR)"\t2b, 4b\n\t"
 325                         ".previous"
 326                         : "=&r" (value), "=r" (res)
 327                         : "r" (addr), "i" (-EFAULT));
 328                 if (res)
 329                         goto fault;
 330                 compute_return_epc(regs);
 331                 regs->regs[insn.i_format.rt] = value;
 332                 break;
 333 #endif /* CONFIG_64BIT */
 334
 335                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 336                 goto sigill;
 337
 338         case sh_op:
 339                 if (!access_ok(VERIFY_WRITE, addr, 2))
 340                         goto sigbus;
 341
 342                 value = regs->regs[insn.i_format.rt];
 343                 __asm__ __volatile__ (
 344 #ifdef __BIG_ENDIAN
 345                         ".set\tnoat\n"
 346                         "1:\tsb\t%1, 1(%2)\n\t"
 347                         "srl\t$1, %1, 0x8\n"
 348                         "2:\tsb\t$1, 0(%2)\n\t"
 349                         ".set\tat\n\t"
 350 #endif
 351 #ifdef __LITTLE_ENDIAN
 352                         ".set\tnoat\n"
 353                         "1:\tsb\t%1, 0(%2)\n\t"
 354                         "srl\t$1,%1, 0x8\n"
 355                         "2:\tsb\t$1, 1(%2)\n\t"
 356                         ".set\tat\n\t"
 357 #endif
 358                         "li\t%0, 0\n"
 359                         "3:\n\t"
 360                         ".section\t.fixup,\"ax\"\n\t"
 361                         "4:\tli\t%0, %3\n\t"
 362                         "j\t3b\n\t"
 363                         ".previous\n\t"
 364                         ".section\t__ex_table,\"a\"\n\t"
 365                         STR(PTR)"\t1b, 4b\n\t"
 366                         STR(PTR)"\t2b, 4b\n\t"
 367                         ".previous"
 368                         : "=r" (res)
 369                         : "r" (value), "r" (addr), "i" (-EFAULT));
 370                 if (res)
 371                         goto fault;
 372                 compute_return_epc(regs);
 373                 break;
 374
 375         case sw_op:
 376                 if (!access_ok(VERIFY_WRITE, addr, 4))
 377                         goto sigbus;
 378
 379                 value = regs->regs[insn.i_format.rt];
 380                 __asm__ __volatile__ (
 381 #ifdef __BIG_ENDIAN
 382                         "1:\tswl\t%1,(%2)\n"
 383                         "2:\tswr\t%1, 3(%2)\n\t"
 384 #endif
 385 #ifdef __LITTLE_ENDIAN
 386                         "1:\tswl\t%1, 3(%2)\n"
 387                         "2:\tswr\t%1, (%2)\n\t"
 388 #endif
 389                         "li\t%0, 0\n"
 390                         "3:\n\t"
 391                         ".section\t.fixup,\"ax\"\n\t"
 392                         "4:\tli\t%0, %3\n\t"
 393                         "j\t3b\n\t"
 394                         ".previous\n\t"
 395                         ".section\t__ex_table,\"a\"\n\t"
 396                         STR(PTR)"\t1b, 4b\n\t"
 397                         STR(PTR)"\t2b, 4b\n\t"
 398                         ".previous"
 399                 : "=r" (res)
 400                 : "r" (value), "r" (addr), "i" (-EFAULT));
 401                 if (res)
 402                         goto fault;
 403                 compute_return_epc(regs);
 404                 break;
 405
 406         case sd_op:
 407 #ifdef CONFIG_64BIT
 408                 /*
 409                  * A 32-bit kernel might be running on a 64-bit processor.  But
 410                  * if we're on a 32-bit processor and an i-cache incoherency
 411                  * or race makes us see a 64-bit instruction here the sdl/sdr
 412                  * would blow up, so for now we don't handle unaligned 64-bit
 413                  * instructions on 32-bit kernels.
 414                  */
 415                 if (!access_ok(VERIFY_WRITE, addr, 8))
 416                         goto sigbus;
 417
 418                 value = regs->regs[insn.i_format.rt];
 419                 __asm__ __volatile__ (
 420 #ifdef __BIG_ENDIAN
 421                         "1:\tsdl\t%1,(%2)\n"
 422                         "2:\tsdr\t%1, 7(%2)\n\t"
 423 #endif
 424 #ifdef __LITTLE_ENDIAN
 425                         "1:\tsdl\t%1, 7(%2)\n"
 426                         "2:\tsdr\t%1, (%2)\n\t"
 427 #endif
 428                         "li\t%0, 0\n"
 429                         "3:\n\t"
 430                         ".section\t.fixup,\"ax\"\n\t"
 431                         "4:\tli\t%0, %3\n\t"
 432                         "j\t3b\n\t"
 433                         ".previous\n\t"
 434                         ".section\t__ex_table,\"a\"\n\t"
 435                         STR(PTR)"\t1b, 4b\n\t"
 436                         STR(PTR)"\t2b, 4b\n\t"
 437                         ".previous"
 438                 : "=r" (res)
 439                 : "r" (value), "r" (addr), "i" (-EFAULT));
 440                 if (res)
 441                         goto fault;
 442                 compute_return_epc(regs);
 443                 break;
 444 #endif /* CONFIG_64BIT */
 445
 446                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 447                 goto sigill;
 448
 449         case lwc1_op:
 450         case ldc1_op:
 451         case swc1_op:
 452         case sdc1_op:
 453                 /*
 454                  * I herewith declare: this does not happen.  So send SIGBUS.
 455                  */
 456                 goto sigbus;
 457
 458         /*
 459          * COP2 is available to implementor for application specific use.
 460          * It's up to applications to register a notifier chain and do
 461          * whatever they have to do, including possible sending of signals.
 462          */
 463         case lwc2_op:
 464                 cu2_notifier_call_chain(CU2_LWC2_OP, regs);
 465                 break;
 466
 467         case ldc2_op:
 468                 cu2_notifier_call_chain(CU2_LDC2_OP, regs);
 469                 break;
 470
 471         case swc2_op:
 472                 cu2_notifier_call_chain(CU2_SWC2_OP, regs);
 473                 break;
 474
 475         case sdc2_op:
 476                 cu2_notifier_call_chain(CU2_SDC2_OP, regs);
 477                 break;
 478
 479         default:
 480                 /*
 481                  * Pheeee...  We encountered an yet unknown instruction or
 482                  * cache coherence problem.  Die sucker, die ...
 483                  */
 484                 goto sigill;
 485         }
 486
 487 #ifdef CONFIG_DEBUG_FS
 488         unaligned_instructions++;
 489 #endif
 490
 491         return;
 492
 493 fault:
 494         /* Did we have an exception handler installed? */
 495         if (fixup_exception(regs))
 496                 return;
 497
 498         die_if_kernel("Unhandled kernel unaligned access", regs);
 499         force_sig(SIGSEGV, current);
 500
 501         return;
 502
 503 sigbus:
 504         die_if_kernel("Unhandled kernel unaligned access", regs);
 505         force_sig(SIGBUS, current);
 506
 507         return;
 508
 509 sigill:
 510         die_if_kernel("Unhandled kernel unaligned access or invalid instruction", regs);
 511         force_sig(SIGILL, current);
 512 }
 513
 514 asmlinkage void do_ade(struct pt_regs *regs)
 515 {
 516         unsigned int __user *pc;
 517         mm_segment_t seg;
 518
 519         perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS,
 520                         1, 0, regs, regs->cp0_badvaddr);
 521         /*
 522          * Did we catch a fault trying to load an instruction?
 523          * Or are we running in MIPS16 mode?
 524          */
 525         if ((regs->cp0_badvaddr == regs->cp0_epc) || (regs->cp0_epc & 0x1))
 526                 goto sigbus;
 527
 528         pc = (unsigned int __user *) exception_epc(regs);
 529         if (user_mode(regs) && !test_thread_flag(TIF_FIXADE))
 530                 goto sigbus;
 531         if (unaligned_action == UNALIGNED_ACTION_SIGNAL)
 532                 goto sigbus;
 533         else if (unaligned_action == UNALIGNED_ACTION_SHOW)
 534                 show_registers(regs);
 535
 536         /*
 537          * Do branch emulation only if we didn't forward the exception.
 538          * This is all so but ugly ...
 539          */
 540         seg = get_fs();
 541         if (!user_mode(regs))
 542                 set_fs(KERNEL_DS);
 543         emulate_load_store_insn(regs, (void __user *)regs->cp0_badvaddr, pc);
 544         set_fs(seg);
 545
 546         return;
 547
 548 sigbus:
 549         die_if_kernel("Kernel unaligned instruction access", regs);
 550         force_sig(SIGBUS, current);
 551
 552         /*
 553          * XXX On return from the signal handler we should advance the epc
 554          */
 555 }
 556
 557 #ifdef CONFIG_DEBUG_FS
 558 extern struct dentry *mips_debugfs_dir;
 559 static int __init debugfs_unaligned(void)
 560 {
 561         struct dentry *d;
 562
 563         if (!mips_debugfs_dir)
 564                 return -ENODEV;
 565         d = debugfs_create_u32("unaligned_instructions", S_IRUGO,
 566                                mips_debugfs_dir, &unaligned_instructions);
 567         if (!d)
 568                 return -ENOMEM;
 569         d = debugfs_create_u32("unaligned_action", S_IRUGO | S_IWUSR,
 570                                mips_debugfs_dir, &unaligned_action);
 571         if (!d)
 572                 return -ENOMEM;
 573         return 0;
 574 }
 575 __initcall(debugfs_unaligned);
 576 #endif