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 <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 enum {
  92         UNALIGNED_ACTION_QUIET,
  93         UNALIGNED_ACTION_SIGNAL,
  94         UNALIGNED_ACTION_SHOW,
  95 };
  96 #ifdef CONFIG_DEBUG_FS
  97 static u32 unaligned_instructions;
  98 static u32 unaligned_action;
  99 #else
 100 #define unaligned_action UNALIGNED_ACTION_QUIET
 101 #endif
 102 extern void show_registers(struct pt_regs *regs);
 103
 104 static void emulate_load_store_insn(struct pt_regs *regs,
 105         void __user *addr, unsigned int __user *pc)
 106 {
 107         union mips_instruction insn;
 108         unsigned long value;
 109         unsigned int res;
 110
 111         regs->regs[0] = 0;
 112
 113         /*
 114          * This load never faults.
 115          */
 116         __get_user(insn.word, pc);
 117
 118         switch (insn.i_format.opcode) {
 119         /*
 120          * These are instructions that a compiler doesn't generate.  We
 121          * can assume therefore that the code is MIPS-aware and
 122          * really buggy.  Emulating these instructions would break the
 123          * semantics anyway.
 124          */
 125         case ll_op:
 126         case lld_op:
 127         case sc_op:
 128         case scd_op:
 129
 130         /*
 131          * For these instructions the only way to create an address
 132          * error is an attempted access to kernel/supervisor address
 133          * space.
 134          */
 135         case ldl_op:
 136         case ldr_op:
 137         case lwl_op:
 138         case lwr_op:
 139         case sdl_op:
 140         case sdr_op:
 141         case swl_op:
 142         case swr_op:
 143         case lb_op:
 144         case lbu_op:
 145         case sb_op:
 146                 goto sigbus;
 147
 148         /*
 149          * The remaining opcodes are the ones that are really of interest.
 150          */
 151         case lh_op:
 152                 if (!access_ok(VERIFY_READ, addr, 2))
 153                         goto sigbus;
 154
 155                 __asm__ __volatile__ (".set\tnoat\n"
 156 #ifdef __BIG_ENDIAN
 157                         "1:\tlb\t%0, 0(%2)\n"
 158                         "2:\tlbu\t$1, 1(%2)\n\t"
 159 #endif
 160 #ifdef __LITTLE_ENDIAN
 161                         "1:\tlb\t%0, 1(%2)\n"
 162                         "2:\tlbu\t$1, 0(%2)\n\t"
 163 #endif
 164                         "sll\t%0, 0x8\n\t"
 165                         "or\t%0, $1\n\t"
 166                         "li\t%1, 0\n"
 167                         "3:\t.set\tat\n\t"
 168                         ".section\t.fixup,\"ax\"\n\t"
 169                         "4:\tli\t%1, %3\n\t"
 170                         "j\t3b\n\t"
 171                         ".previous\n\t"
 172                         ".section\t__ex_table,\"a\"\n\t"
 173                         STR(PTR)"\t1b, 4b\n\t"
 174                         STR(PTR)"\t2b, 4b\n\t"
 175                         ".previous"
 176                         : "=&r" (value), "=r" (res)
 177                         : "r" (addr), "i" (-EFAULT));
 178                 if (res)
 179                         goto fault;
 180                 compute_return_epc(regs);
 181                 regs->regs[insn.i_format.rt] = value;
 182                 break;
 183
 184         case lw_op:
 185                 if (!access_ok(VERIFY_READ, addr, 4))
 186                         goto sigbus;
 187
 188                 __asm__ __volatile__ (
 189 #ifdef __BIG_ENDIAN
 190                         "1:\tlwl\t%0, (%2)\n"
 191                         "2:\tlwr\t%0, 3(%2)\n\t"
 192 #endif
 193 #ifdef __LITTLE_ENDIAN
 194                         "1:\tlwl\t%0, 3(%2)\n"
 195                         "2:\tlwr\t%0, (%2)\n\t"
 196 #endif
 197                         "li\t%1, 0\n"
 198                         "3:\t.section\t.fixup,\"ax\"\n\t"
 199                         "4:\tli\t%1, %3\n\t"
 200                         "j\t3b\n\t"
 201                         ".previous\n\t"
 202                         ".section\t__ex_table,\"a\"\n\t"
 203                         STR(PTR)"\t1b, 4b\n\t"
 204                         STR(PTR)"\t2b, 4b\n\t"
 205                         ".previous"
 206                         : "=&r" (value), "=r" (res)
 207                         : "r" (addr), "i" (-EFAULT));
 208                 if (res)
 209                         goto fault;
 210                 compute_return_epc(regs);
 211                 regs->regs[insn.i_format.rt] = value;
 212                 break;
 213
 214         case lhu_op:
 215                 if (!access_ok(VERIFY_READ, addr, 2))
 216                         goto sigbus;
 217
 218                 __asm__ __volatile__ (
 219                         ".set\tnoat\n"
 220 #ifdef __BIG_ENDIAN
 221                         "1:\tlbu\t%0, 0(%2)\n"
 222                         "2:\tlbu\t$1, 1(%2)\n\t"
 223 #endif
 224 #ifdef __LITTLE_ENDIAN
 225                         "1:\tlbu\t%0, 1(%2)\n"
 226                         "2:\tlbu\t$1, 0(%2)\n\t"
 227 #endif
 228                         "sll\t%0, 0x8\n\t"
 229                         "or\t%0, $1\n\t"
 230                         "li\t%1, 0\n"
 231                         "3:\t.set\tat\n\t"
 232                         ".section\t.fixup,\"ax\"\n\t"
 233                         "4:\tli\t%1, %3\n\t"
 234                         "j\t3b\n\t"
 235                         ".previous\n\t"
 236                         ".section\t__ex_table,\"a\"\n\t"
 237                         STR(PTR)"\t1b, 4b\n\t"
 238                         STR(PTR)"\t2b, 4b\n\t"
 239                         ".previous"
 240                         : "=&r" (value), "=r" (res)
 241                         : "r" (addr), "i" (-EFAULT));
 242                 if (res)
 243                         goto fault;
 244                 compute_return_epc(regs);
 245                 regs->regs[insn.i_format.rt] = value;
 246                 break;
 247
 248         case lwu_op:
 249 #ifdef CONFIG_64BIT
 250                 /*
 251                  * A 32-bit kernel might be running on a 64-bit processor.  But
 252                  * if we're on a 32-bit processor and an i-cache incoherency
 253                  * or race makes us see a 64-bit instruction here the sdl/sdr
 254                  * would blow up, so for now we don't handle unaligned 64-bit
 255                  * instructions on 32-bit kernels.
 256                  */
 257                 if (!access_ok(VERIFY_READ, addr, 4))
 258                         goto sigbus;
 259
 260                 __asm__ __volatile__ (
 261 #ifdef __BIG_ENDIAN
 262                         "1:\tlwl\t%0, (%2)\n"
 263                         "2:\tlwr\t%0, 3(%2)\n\t"
 264 #endif
 265 #ifdef __LITTLE_ENDIAN
 266                         "1:\tlwl\t%0, 3(%2)\n"
 267                         "2:\tlwr\t%0, (%2)\n\t"
 268 #endif
 269                         "dsll\t%0, %0, 32\n\t"
 270                         "dsrl\t%0, %0, 32\n\t"
 271                         "li\t%1, 0\n"
 272                         "3:\t.section\t.fixup,\"ax\"\n\t"
 273                         "4:\tli\t%1, %3\n\t"
 274                         "j\t3b\n\t"
 275                         ".previous\n\t"
 276                         ".section\t__ex_table,\"a\"\n\t"
 277                         STR(PTR)"\t1b, 4b\n\t"
 278                         STR(PTR)"\t2b, 4b\n\t"
 279                         ".previous"
 280                         : "=&r" (value), "=r" (res)
 281                         : "r" (addr), "i" (-EFAULT));
 282                 if (res)
 283                         goto fault;
 284                 compute_return_epc(regs);
 285                 regs->regs[insn.i_format.rt] = value;
 286                 break;
 287 #endif /* CONFIG_64BIT */
 288
 289                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 290                 goto sigill;
 291
 292         case ld_op:
 293 #ifdef CONFIG_64BIT
 294                 /*
 295                  * A 32-bit kernel might be running on a 64-bit processor.  But
 296                  * if we're on a 32-bit processor and an i-cache incoherency
 297                  * or race makes us see a 64-bit instruction here the sdl/sdr
 298                  * would blow up, so for now we don't handle unaligned 64-bit
 299                  * instructions on 32-bit kernels.
 300                  */
 301                 if (!access_ok(VERIFY_READ, addr, 8))
 302                         goto sigbus;
 303
 304                 __asm__ __volatile__ (
 305 #ifdef __BIG_ENDIAN
 306                         "1:\tldl\t%0, (%2)\n"
 307                         "2:\tldr\t%0, 7(%2)\n\t"
 308 #endif
 309 #ifdef __LITTLE_ENDIAN
 310                         "1:\tldl\t%0, 7(%2)\n"
 311                         "2:\tldr\t%0, (%2)\n\t"
 312 #endif
 313                         "li\t%1, 0\n"
 314                         "3:\t.section\t.fixup,\"ax\"\n\t"
 315                         "4:\tli\t%1, %3\n\t"
 316                         "j\t3b\n\t"
 317                         ".previous\n\t"
 318                         ".section\t__ex_table,\"a\"\n\t"
 319                         STR(PTR)"\t1b, 4b\n\t"
 320                         STR(PTR)"\t2b, 4b\n\t"
 321                         ".previous"
 322                         : "=&r" (value), "=r" (res)
 323                         : "r" (addr), "i" (-EFAULT));
 324                 if (res)
 325                         goto fault;
 326                 compute_return_epc(regs);
 327                 regs->regs[insn.i_format.rt] = value;
 328                 break;
 329 #endif /* CONFIG_64BIT */
 330
 331                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 332                 goto sigill;
 333
 334         case sh_op:
 335                 if (!access_ok(VERIFY_WRITE, addr, 2))
 336                         goto sigbus;
 337
 338                 value = regs->regs[insn.i_format.rt];
 339                 __asm__ __volatile__ (
 340 #ifdef __BIG_ENDIAN
 341                         ".set\tnoat\n"
 342                         "1:\tsb\t%1, 1(%2)\n\t"
 343                         "srl\t$1, %1, 0x8\n"
 344                         "2:\tsb\t$1, 0(%2)\n\t"
 345                         ".set\tat\n\t"
 346 #endif
 347 #ifdef __LITTLE_ENDIAN
 348                         ".set\tnoat\n"
 349                         "1:\tsb\t%1, 0(%2)\n\t"
 350                         "srl\t$1,%1, 0x8\n"
 351                         "2:\tsb\t$1, 1(%2)\n\t"
 352                         ".set\tat\n\t"
 353 #endif
 354                         "li\t%0, 0\n"
 355                         "3:\n\t"
 356                         ".section\t.fixup,\"ax\"\n\t"
 357                         "4:\tli\t%0, %3\n\t"
 358                         "j\t3b\n\t"
 359                         ".previous\n\t"
 360                         ".section\t__ex_table,\"a\"\n\t"
 361                         STR(PTR)"\t1b, 4b\n\t"
 362                         STR(PTR)"\t2b, 4b\n\t"
 363                         ".previous"
 364                         : "=r" (res)
 365                         : "r" (value), "r" (addr), "i" (-EFAULT));
 366                 if (res)
 367                         goto fault;
 368                 compute_return_epc(regs);
 369                 break;
 370
 371         case sw_op:
 372                 if (!access_ok(VERIFY_WRITE, addr, 4))
 373                         goto sigbus;
 374
 375                 value = regs->regs[insn.i_format.rt];
 376                 __asm__ __volatile__ (
 377 #ifdef __BIG_ENDIAN
 378                         "1:\tswl\t%1,(%2)\n"
 379                         "2:\tswr\t%1, 3(%2)\n\t"
 380 #endif
 381 #ifdef __LITTLE_ENDIAN
 382                         "1:\tswl\t%1, 3(%2)\n"
 383                         "2:\tswr\t%1, (%2)\n\t"
 384 #endif
 385                         "li\t%0, 0\n"
 386                         "3:\n\t"
 387                         ".section\t.fixup,\"ax\"\n\t"
 388                         "4:\tli\t%0, %3\n\t"
 389                         "j\t3b\n\t"
 390                         ".previous\n\t"
 391                         ".section\t__ex_table,\"a\"\n\t"
 392                         STR(PTR)"\t1b, 4b\n\t"
 393                         STR(PTR)"\t2b, 4b\n\t"
 394                         ".previous"
 395                 : "=r" (res)
 396                 : "r" (value), "r" (addr), "i" (-EFAULT));
 397                 if (res)
 398                         goto fault;
 399                 compute_return_epc(regs);
 400                 break;
 401
 402         case sd_op:
 403 #ifdef CONFIG_64BIT
 404                 /*
 405                  * A 32-bit kernel might be running on a 64-bit processor.  But
 406                  * if we're on a 32-bit processor and an i-cache incoherency
 407                  * or race makes us see a 64-bit instruction here the sdl/sdr
 408                  * would blow up, so for now we don't handle unaligned 64-bit
 409                  * instructions on 32-bit kernels.
 410                  */
 411                 if (!access_ok(VERIFY_WRITE, addr, 8))
 412                         goto sigbus;
 413
 414                 value = regs->regs[insn.i_format.rt];
 415                 __asm__ __volatile__ (
 416 #ifdef __BIG_ENDIAN
 417                         "1:\tsdl\t%1,(%2)\n"
 418                         "2:\tsdr\t%1, 7(%2)\n\t"
 419 #endif
 420 #ifdef __LITTLE_ENDIAN
 421                         "1:\tsdl\t%1, 7(%2)\n"
 422                         "2:\tsdr\t%1, (%2)\n\t"
 423 #endif
 424                         "li\t%0, 0\n"
 425                         "3:\n\t"
 426                         ".section\t.fixup,\"ax\"\n\t"
 427                         "4:\tli\t%0, %3\n\t"
 428                         "j\t3b\n\t"
 429                         ".previous\n\t"
 430                         ".section\t__ex_table,\"a\"\n\t"
 431                         STR(PTR)"\t1b, 4b\n\t"
 432                         STR(PTR)"\t2b, 4b\n\t"
 433                         ".previous"
 434                 : "=r" (res)
 435                 : "r" (value), "r" (addr), "i" (-EFAULT));
 436                 if (res)
 437                         goto fault;
 438                 compute_return_epc(regs);
 439                 break;
 440 #endif /* CONFIG_64BIT */
 441
 442                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 443                 goto sigill;
 444
 445         case lwc1_op:
 446         case ldc1_op:
 447         case swc1_op:
 448         case sdc1_op:
 449                 /*
 450                  * I herewith declare: this does not happen.  So send SIGBUS.
 451                  */
 452                 goto sigbus;
 453
 454         case lwc2_op:
 455         case ldc2_op:
 456         case swc2_op:
 457         case sdc2_op:
 458                 /*
 459                  * These are the coprocessor 2 load/stores.  The current
 460                  * implementations don't use cp2 and cp2 should always be
 461                  * disabled in c0_status.  So send SIGILL.
 462                  * (No longer true: The Sony Praystation uses cp2 for
 463                  * 3D matrix operations.  Dunno if that thingy has a MMU ...)
 464                  */
 465         default:
 466                 /*
 467                  * Pheeee...  We encountered an yet unknown instruction or
 468                  * cache coherence problem.  Die sucker, die ...
 469                  */
 470                 goto sigill;
 471         }
 472
 473 #ifdef CONFIG_DEBUG_FS
 474         unaligned_instructions++;
 475 #endif
 476
 477         return;
 478
 479 fault:
 480         /* Did we have an exception handler installed? */
 481         if (fixup_exception(regs))
 482                 return;
 483
 484         die_if_kernel("Unhandled kernel unaligned access", regs);
 485         send_sig(SIGSEGV, current, 1);
 486
 487         return;
 488
 489 sigbus:
 490         die_if_kernel("Unhandled kernel unaligned access", regs);
 491         send_sig(SIGBUS, current, 1);
 492
 493         return;
 494
 495 sigill:
 496         die_if_kernel("Unhandled kernel unaligned access or invalid instruction", regs);
 497         send_sig(SIGILL, current, 1);
 498 }
 499
 500 asmlinkage void do_ade(struct pt_regs *regs)
 501 {
 502         extern int do_dsemulret(struct pt_regs *);
 503         unsigned int __user *pc;
 504         mm_segment_t seg;
 505
 506         /*
 507          * Address errors may be deliberately induced by the FPU emulator to
 508          * retake control of the CPU after executing the instruction in the
 509          * delay slot of an emulated branch.
 510          */
 511         /* Terminate if exception was recognized as a delay slot return */
 512         if (do_dsemulret(regs))
 513                 return;
 514
 515         /* Otherwise handle as normal */
 516
 517         /*
 518          * Did we catch a fault trying to load an instruction?
 519          * Or are we running in MIPS16 mode?
 520          */
 521         if ((regs->cp0_badvaddr == regs->cp0_epc) || (regs->cp0_epc & 0x1))
 522                 goto sigbus;
 523
 524         pc = (unsigned int __user *) exception_epc(regs);
 525         if (user_mode(regs) && !test_thread_flag(TIF_FIXADE))
 526                 goto sigbus;
 527         if (unaligned_action == UNALIGNED_ACTION_SIGNAL)
 528                 goto sigbus;
 529         else if (unaligned_action == UNALIGNED_ACTION_SHOW)
 530                 show_registers(regs);
 531
 532         /*
 533          * Do branch emulation only if we didn't forward the exception.
 534          * This is all so but ugly ...
 535          */
 536         seg = get_fs();
 537         if (!user_mode(regs))
 538                 set_fs(KERNEL_DS);
 539         emulate_load_store_insn(regs, (void __user *)regs->cp0_badvaddr, pc);
 540         set_fs(seg);
 541
 542         return;
 543
 544 sigbus:
 545         die_if_kernel("Kernel unaligned instruction access", regs);
 546         force_sig(SIGBUS, current);
 547
 548         /*
 549          * XXX On return from the signal handler we should advance the epc
 550          */
 551 }
 552
 553 #ifdef CONFIG_DEBUG_FS
 554 extern struct dentry *mips_debugfs_dir;
 555 static int __init debugfs_unaligned(void)
 556 {
 557         struct dentry *d;
 558
 559         if (!mips_debugfs_dir)
 560                 return -ENODEV;
 561         d = debugfs_create_u32("unaligned_instructions", S_IRUGO,
 562                                mips_debugfs_dir, &unaligned_instructions);
 563         if (IS_ERR(d))
 564                 return PTR_ERR(d);
 565         d = debugfs_create_u32("unaligned_action", S_IRUGO | S_IWUSR,
 566                                mips_debugfs_dir, &unaligned_action);
 567         if (IS_ERR(d))
 568                 return PTR_ERR(d);
 569         return 0;
 570 }
 571 __initcall(debugfs_unaligned);
 572 #endif