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/config.h>
  76 #include <linux/mm.h>
  77 #include <linux/module.h>
  78 #include <linux/signal.h>
  79 #include <linux/smp.h>
  80 #include <linux/smp_lock.h>
  81
  82 #include <asm/asm.h>
  83 #include <asm/branch.h>
  84 #include <asm/byteorder.h>
  85 #include <asm/inst.h>
  86 #include <asm/uaccess.h>
  87 #include <asm/system.h>
  88
  89 #define STR(x)  __STR(x)
  90 #define __STR(x)  #x
  91
  92 #ifdef CONFIG_PROC_FS
  93 unsigned long unaligned_instructions;
  94 #endif
  95
  96 static inline int emulate_load_store_insn(struct pt_regs *regs,
  97         void __user *addr, unsigned int __user *pc,
  98         unsigned long **regptr, unsigned long *newvalue)
  99 {
 100         union mips_instruction insn;
 101         unsigned long value;
 102         unsigned int res;
 103
 104         regs->regs[0] = 0;
 105         *regptr=NULL;
 106
 107         /*
 108          * This load never faults.
 109          */
 110         __get_user(insn.word, pc);
 111
 112         switch (insn.i_format.opcode) {
 113         /*
 114          * These are instructions that a compiler doesn't generate.  We
 115          * can assume therefore that the code is MIPS-aware and
 116          * really buggy.  Emulating these instructions would break the
 117          * semantics anyway.
 118          */
 119         case ll_op:
 120         case lld_op:
 121         case sc_op:
 122         case scd_op:
 123
 124         /*
 125          * For these instructions the only way to create an address
 126          * error is an attempted access to kernel/supervisor address
 127          * space.
 128          */
 129         case ldl_op:
 130         case ldr_op:
 131         case lwl_op:
 132         case lwr_op:
 133         case sdl_op:
 134         case sdr_op:
 135         case swl_op:
 136         case swr_op:
 137         case lb_op:
 138         case lbu_op:
 139         case sb_op:
 140                 goto sigbus;
 141
 142         /*
 143          * The remaining opcodes are the ones that are really of interest.
 144          */
 145         case lh_op:
 146                 if (!access_ok(VERIFY_READ, addr, 2))
 147                         goto sigbus;
 148
 149                 __asm__ __volatile__ (".set\tnoat\n"
 150 #ifdef __BIG_ENDIAN
 151                         "1:\tlb\t%0, 0(%2)\n"
 152                         "2:\tlbu\t$1, 1(%2)\n\t"
 153 #endif
 154 #ifdef __LITTLE_ENDIAN
 155                         "1:\tlb\t%0, 1(%2)\n"
 156                         "2:\tlbu\t$1, 0(%2)\n\t"
 157 #endif
 158                         "sll\t%0, 0x8\n\t"
 159                         "or\t%0, $1\n\t"
 160                         "li\t%1, 0\n"
 161                         "3:\t.set\tat\n\t"
 162                         ".section\t.fixup,\"ax\"\n\t"
 163                         "4:\tli\t%1, %3\n\t"
 164                         "j\t3b\n\t"
 165                         ".previous\n\t"
 166                         ".section\t__ex_table,\"a\"\n\t"
 167                         STR(PTR)"\t1b, 4b\n\t"
 168                         STR(PTR)"\t2b, 4b\n\t"
 169                         ".previous"
 170                         : "=&r" (value), "=r" (res)
 171                         : "r" (addr), "i" (-EFAULT));
 172                 if (res)
 173                         goto fault;
 174                 *newvalue = value;
 175                 *regptr = &regs->regs[insn.i_format.rt];
 176                 break;
 177
 178         case lw_op:
 179                 if (!access_ok(VERIFY_READ, addr, 4))
 180                         goto sigbus;
 181
 182                 __asm__ __volatile__ (
 183 #ifdef __BIG_ENDIAN
 184                         "1:\tlwl\t%0, (%2)\n"
 185                         "2:\tlwr\t%0, 3(%2)\n\t"
 186 #endif
 187 #ifdef __LITTLE_ENDIAN
 188                         "1:\tlwl\t%0, 3(%2)\n"
 189                         "2:\tlwr\t%0, (%2)\n\t"
 190 #endif
 191                         "li\t%1, 0\n"
 192                         "3:\t.section\t.fixup,\"ax\"\n\t"
 193                         "4:\tli\t%1, %3\n\t"
 194                         "j\t3b\n\t"
 195                         ".previous\n\t"
 196                         ".section\t__ex_table,\"a\"\n\t"
 197                         STR(PTR)"\t1b, 4b\n\t"
 198                         STR(PTR)"\t2b, 4b\n\t"
 199                         ".previous"
 200                         : "=&r" (value), "=r" (res)
 201                         : "r" (addr), "i" (-EFAULT));
 202                 if (res)
 203                         goto fault;
 204                 *newvalue = value;
 205                 *regptr = &regs->regs[insn.i_format.rt];
 206                 break;
 207
 208         case lhu_op:
 209                 if (!access_ok(VERIFY_READ, addr, 2))
 210                         goto sigbus;
 211
 212                 __asm__ __volatile__ (
 213                         ".set\tnoat\n"
 214 #ifdef __BIG_ENDIAN
 215                         "1:\tlbu\t%0, 0(%2)\n"
 216                         "2:\tlbu\t$1, 1(%2)\n\t"
 217 #endif
 218 #ifdef __LITTLE_ENDIAN
 219                         "1:\tlbu\t%0, 1(%2)\n"
 220                         "2:\tlbu\t$1, 0(%2)\n\t"
 221 #endif
 222                         "sll\t%0, 0x8\n\t"
 223                         "or\t%0, $1\n\t"
 224                         "li\t%1, 0\n"
 225                         "3:\t.set\tat\n\t"
 226                         ".section\t.fixup,\"ax\"\n\t"
 227                         "4:\tli\t%1, %3\n\t"
 228                         "j\t3b\n\t"
 229                         ".previous\n\t"
 230                         ".section\t__ex_table,\"a\"\n\t"
 231                         STR(PTR)"\t1b, 4b\n\t"
 232                         STR(PTR)"\t2b, 4b\n\t"
 233                         ".previous"
 234                         : "=&r" (value), "=r" (res)
 235                         : "r" (addr), "i" (-EFAULT));
 236                 if (res)
 237                         goto fault;
 238                 *newvalue = value;
 239                 *regptr = &regs->regs[insn.i_format.rt];
 240                 break;
 241
 242         case lwu_op:
 243 #ifdef CONFIG_64BIT
 244                 /*
 245                  * A 32-bit kernel might be running on a 64-bit processor.  But
 246                  * if we're on a 32-bit processor and an i-cache incoherency
 247                  * or race makes us see a 64-bit instruction here the sdl/sdr
 248                  * would blow up, so for now we don't handle unaligned 64-bit
 249                  * instructions on 32-bit kernels.
 250                  */
 251                 if (!access_ok(VERIFY_READ, addr, 4))
 252                         goto sigbus;
 253
 254                 __asm__ __volatile__ (
 255 #ifdef __BIG_ENDIAN
 256                         "1:\tlwl\t%0, (%2)\n"
 257                         "2:\tlwr\t%0, 3(%2)\n\t"
 258 #endif
 259 #ifdef __LITTLE_ENDIAN
 260                         "1:\tlwl\t%0, 3(%2)\n"
 261                         "2:\tlwr\t%0, (%2)\n\t"
 262 #endif
 263                         "dsll\t%0, %0, 32\n\t"
 264                         "dsrl\t%0, %0, 32\n\t"
 265                         "li\t%1, 0\n"
 266                         "3:\t.section\t.fixup,\"ax\"\n\t"
 267                         "4:\tli\t%1, %3\n\t"
 268                         "j\t3b\n\t"
 269                         ".previous\n\t"
 270                         ".section\t__ex_table,\"a\"\n\t"
 271                         STR(PTR)"\t1b, 4b\n\t"
 272                         STR(PTR)"\t2b, 4b\n\t"
 273                         ".previous"
 274                         : "=&r" (value), "=r" (res)
 275                         : "r" (addr), "i" (-EFAULT));
 276                 if (res)
 277                         goto fault;
 278                 *newvalue = value;
 279                 *regptr = &regs->regs[insn.i_format.rt];
 280                 break;
 281 #endif /* CONFIG_64BIT */
 282
 283                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 284                 goto sigill;
 285
 286         case ld_op:
 287 #ifdef CONFIG_64BIT
 288                 /*
 289                  * A 32-bit kernel might be running on a 64-bit processor.  But
 290                  * if we're on a 32-bit processor and an i-cache incoherency
 291                  * or race makes us see a 64-bit instruction here the sdl/sdr
 292                  * would blow up, so for now we don't handle unaligned 64-bit
 293                  * instructions on 32-bit kernels.
 294                  */
 295                 if (!access_ok(VERIFY_READ, addr, 8))
 296                         goto sigbus;
 297
 298                 __asm__ __volatile__ (
 299 #ifdef __BIG_ENDIAN
 300                         "1:\tldl\t%0, (%2)\n"
 301                         "2:\tldr\t%0, 7(%2)\n\t"
 302 #endif
 303 #ifdef __LITTLE_ENDIAN
 304                         "1:\tldl\t%0, 7(%2)\n"
 305                         "2:\tldr\t%0, (%2)\n\t"
 306 #endif
 307                         "li\t%1, 0\n"
 308                         "3:\t.section\t.fixup,\"ax\"\n\t"
 309                         "4:\tli\t%1, %3\n\t"
 310                         "j\t3b\n\t"
 311                         ".previous\n\t"
 312                         ".section\t__ex_table,\"a\"\n\t"
 313                         STR(PTR)"\t1b, 4b\n\t"
 314                         STR(PTR)"\t2b, 4b\n\t"
 315                         ".previous"
 316                         : "=&r" (value), "=r" (res)
 317                         : "r" (addr), "i" (-EFAULT));
 318                 if (res)
 319                         goto fault;
 320                 *newvalue = value;
 321                 *regptr = &regs->regs[insn.i_format.rt];
 322                 break;
 323 #endif /* CONFIG_64BIT */
 324
 325                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 326                 goto sigill;
 327
 328         case sh_op:
 329                 if (!access_ok(VERIFY_WRITE, addr, 2))
 330                         goto sigbus;
 331
 332                 value = regs->regs[insn.i_format.rt];
 333                 __asm__ __volatile__ (
 334 #ifdef __BIG_ENDIAN
 335                         ".set\tnoat\n"
 336                         "1:\tsb\t%1, 1(%2)\n\t"
 337                         "srl\t$1, %1, 0x8\n"
 338                         "2:\tsb\t$1, 0(%2)\n\t"
 339                         ".set\tat\n\t"
 340 #endif
 341 #ifdef __LITTLE_ENDIAN
 342                         ".set\tnoat\n"
 343                         "1:\tsb\t%1, 0(%2)\n\t"
 344                         "srl\t$1,%1, 0x8\n"
 345                         "2:\tsb\t$1, 1(%2)\n\t"
 346                         ".set\tat\n\t"
 347 #endif
 348                         "li\t%0, 0\n"
 349                         "3:\n\t"
 350                         ".section\t.fixup,\"ax\"\n\t"
 351                         "4:\tli\t%0, %3\n\t"
 352                         "j\t3b\n\t"
 353                         ".previous\n\t"
 354                         ".section\t__ex_table,\"a\"\n\t"
 355                         STR(PTR)"\t1b, 4b\n\t"
 356                         STR(PTR)"\t2b, 4b\n\t"
 357                         ".previous"
 358                         : "=r" (res)
 359                         : "r" (value), "r" (addr), "i" (-EFAULT));
 360                 if (res)
 361                         goto fault;
 362                 break;
 363
 364         case sw_op:
 365                 if (!access_ok(VERIFY_WRITE, addr, 4))
 366                         goto sigbus;
 367
 368                 value = regs->regs[insn.i_format.rt];
 369                 __asm__ __volatile__ (
 370 #ifdef __BIG_ENDIAN
 371                         "1:\tswl\t%1,(%2)\n"
 372                         "2:\tswr\t%1, 3(%2)\n\t"
 373 #endif
 374 #ifdef __LITTLE_ENDIAN
 375                         "1:\tswl\t%1, 3(%2)\n"
 376                         "2:\tswr\t%1, (%2)\n\t"
 377 #endif
 378                         "li\t%0, 0\n"
 379                         "3:\n\t"
 380                         ".section\t.fixup,\"ax\"\n\t"
 381                         "4:\tli\t%0, %3\n\t"
 382                         "j\t3b\n\t"
 383                         ".previous\n\t"
 384                         ".section\t__ex_table,\"a\"\n\t"
 385                         STR(PTR)"\t1b, 4b\n\t"
 386                         STR(PTR)"\t2b, 4b\n\t"
 387                         ".previous"
 388                 : "=r" (res)
 389                 : "r" (value), "r" (addr), "i" (-EFAULT));
 390                 if (res)
 391                         goto fault;
 392                 break;
 393
 394         case sd_op:
 395 #ifdef CONFIG_64BIT
 396                 /*
 397                  * A 32-bit kernel might be running on a 64-bit processor.  But
 398                  * if we're on a 32-bit processor and an i-cache incoherency
 399                  * or race makes us see a 64-bit instruction here the sdl/sdr
 400                  * would blow up, so for now we don't handle unaligned 64-bit
 401                  * instructions on 32-bit kernels.
 402                  */
 403                 if (!access_ok(VERIFY_WRITE, addr, 8))
 404                         goto sigbus;
 405
 406                 value = regs->regs[insn.i_format.rt];
 407                 __asm__ __volatile__ (
 408 #ifdef __BIG_ENDIAN
 409                         "1:\tsdl\t%1,(%2)\n"
 410                         "2:\tsdr\t%1, 7(%2)\n\t"
 411 #endif
 412 #ifdef __LITTLE_ENDIAN
 413                         "1:\tsdl\t%1, 7(%2)\n"
 414                         "2:\tsdr\t%1, (%2)\n\t"
 415 #endif
 416                         "li\t%0, 0\n"
 417                         "3:\n\t"
 418                         ".section\t.fixup,\"ax\"\n\t"
 419                         "4:\tli\t%0, %3\n\t"
 420                         "j\t3b\n\t"
 421                         ".previous\n\t"
 422                         ".section\t__ex_table,\"a\"\n\t"
 423                         STR(PTR)"\t1b, 4b\n\t"
 424                         STR(PTR)"\t2b, 4b\n\t"
 425                         ".previous"
 426                 : "=r" (res)
 427                 : "r" (value), "r" (addr), "i" (-EFAULT));
 428                 if (res)
 429                         goto fault;
 430                 break;
 431 #endif /* CONFIG_64BIT */
 432
 433                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 434                 goto sigill;
 435
 436         case lwc1_op:
 437         case ldc1_op:
 438         case swc1_op:
 439         case sdc1_op:
 440                 /*
 441                  * I herewith declare: this does not happen.  So send SIGBUS.
 442                  */
 443                 goto sigbus;
 444
 445         case lwc2_op:
 446         case ldc2_op:
 447         case swc2_op:
 448         case sdc2_op:
 449                 /*
 450                  * These are the coprocessor 2 load/stores.  The current
 451                  * implementations don't use cp2 and cp2 should always be
 452                  * disabled in c0_status.  So send SIGILL.
 453                  * (No longer true: The Sony Praystation uses cp2 for
 454                  * 3D matrix operations.  Dunno if that thingy has a MMU ...)
 455                  */
 456         default:
 457                 /*
 458                  * Pheeee...  We encountered an yet unknown instruction or
 459                  * cache coherence problem.  Die sucker, die ...
 460                  */
 461                 goto sigill;
 462         }
 463
 464 #ifdef CONFIG_PROC_FS
 465         unaligned_instructions++;
 466 #endif
 467
 468         return 0;
 469
 470 fault:
 471         /* Did we have an exception handler installed? */
 472         if (fixup_exception(regs))
 473                 return 1;
 474
 475         die_if_kernel ("Unhandled kernel unaligned access", regs);
 476         send_sig(SIGSEGV, current, 1);
 477
 478         return 0;
 479
 480 sigbus:
 481         die_if_kernel("Unhandled kernel unaligned access", regs);
 482         send_sig(SIGBUS, current, 1);
 483
 484         return 0;
 485
 486 sigill:
 487         die_if_kernel("Unhandled kernel unaligned access or invalid instruction", regs);
 488         send_sig(SIGILL, current, 1);
 489
 490         return 0;
 491 }
 492
 493 asmlinkage void do_ade(struct pt_regs *regs)
 494 {
 495         unsigned long *regptr, newval;
 496         extern int do_dsemulret(struct pt_regs *);
 497         unsigned int __user *pc;
 498         mm_segment_t seg;
 499
 500         /*
 501          * Address errors may be deliberately induced by the FPU emulator to
 502          * retake control of the CPU after executing the instruction in the
 503          * delay slot of an emulated branch.
 504          */
 505         /* Terminate if exception was recognized as a delay slot return */
 506         if (do_dsemulret(regs))
 507                 return;
 508
 509         /* Otherwise handle as normal */
 510
 511         /*
 512          * Did we catch a fault trying to load an instruction?
 513          * Or are we running in MIPS16 mode?
 514          */
 515         if ((regs->cp0_badvaddr == regs->cp0_epc) || (regs->cp0_epc & 0x1))
 516                 goto sigbus;
 517
 518         pc = (unsigned int __user *) exception_epc(regs);
 519         if ((current->thread.mflags & MF_FIXADE) == 0)
 520                 goto sigbus;
 521
 522         /*
 523          * Do branch emulation only if we didn't forward the exception.
 524          * This is all so but ugly ...
 525          */
 526         seg = get_fs();
 527         if (!user_mode(regs))
 528                 set_fs(KERNEL_DS);
 529         if (!emulate_load_store_insn(regs, (void __user *)regs->cp0_badvaddr, pc,
 530                                      &regptr, &newval)) {
 531                 compute_return_epc(regs);
 532                 /*
 533                  * Now that branch is evaluated, update the dest
 534                  * register if necessary
 535                  */
 536                 if (regptr)
 537                         *regptr = newval;
 538         }
 539         set_fs(seg);
 540
 541         return;
 542
 543 sigbus:
 544         die_if_kernel("Kernel unaligned instruction access", regs);
 545         force_sig(SIGBUS, current);
 546
 547         /*
 548          * XXX On return from the signal handler we should advance the epc
 549          */
 550 }