arch/powerpc/kernel/ftrace.c

   1 /*
   2  * Code for replacing ftrace calls with jumps.
   3  *
   4  * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
   5  *
   6  * Thanks goes out to P.A. Semi, Inc for supplying me with a PPC64 box.
   7  *
   8  */
   9
  10 #include <linux/spinlock.h>
  11 #include <linux/hardirq.h>
  12 #include <linux/uaccess.h>
  13 #include <linux/module.h>
  14 #include <linux/ftrace.h>
  15 #include <linux/percpu.h>
  16 #include <linux/init.h>
  17 #include <linux/list.h>
  18
  19 #include <asm/cacheflush.h>
  20 #include <asm/code-patching.h>
  21 #include <asm/ftrace.h>
  22
  23 #if 0
  24 #define DEBUGP printk
  25 #else
  26 #define DEBUGP(fmt , ...)       do { } while (0)
  27 #endif
  28
  29 static unsigned int ftrace_nop = PPC_NOP_INSTR;
  30
  31 #ifdef CONFIG_PPC32
  32 # define GET_ADDR(addr) addr
  33 #else
  34 /* PowerPC64's functions are data that points to the functions */
  35 # define GET_ADDR(addr) (*(unsigned long *)addr)
  36 #endif
  37
  38
  39 static unsigned int ftrace_calc_offset(long ip, long addr)
  40 {
  41         return (int)(addr - ip);
  42 }
  43
  44 static unsigned char *ftrace_nop_replace(void)
  45 {
  46         return (char *)&ftrace_nop;
  47 }
  48
  49 static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
  50 {
  51         static unsigned int op;
  52
  53         /*
  54          * It would be nice to just use create_function_call, but that will
  55          * update the code itself. Here we need to just return the
  56          * instruction that is going to be modified, without modifying the
  57          * code.
  58          */
  59         addr = GET_ADDR(addr);
  60
  61         /* Set to "bl addr" */
  62         op = 0x48000001 | (ftrace_calc_offset(ip, addr) & 0x03fffffc);
  63
  64         /*
  65          * No locking needed, this must be called via kstop_machine
  66          * which in essence is like running on a uniprocessor machine.
  67          */
  68         return (unsigned char *)&op;
  69 }
  70
  71 #ifdef CONFIG_PPC64
  72 # define _ASM_ALIGN     " .align 3 "
  73 # define _ASM_PTR       " .llong "
  74 #else
  75 # define _ASM_ALIGN     " .align 2 "
  76 # define _ASM_PTR       " .long "
  77 #endif
  78
  79 static int
  80 ftrace_modify_code(unsigned long ip, unsigned char *old_code,
  81                    unsigned char *new_code)
  82 {
  83         unsigned char replaced[MCOUNT_INSN_SIZE];
  84
  85         /*
  86          * Note: Due to modules and __init, code can
  87          *  disappear and change, we need to protect against faulting
  88          *  as well as code changing. We do this by using the
  89          *  probe_kernel_* functions.
  90          *
  91          * No real locking needed, this code is run through
  92          * kstop_machine, or before SMP starts.
  93          */
  94
  95         /* read the text we want to modify */
  96         if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
  97                 return -EFAULT;
  98
  99         /* Make sure it is what we expect it to be */
 100         if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
 101                 return -EINVAL;
 102
 103         /* replace the text with the new text */
 104         if (probe_kernel_write((void *)ip, new_code, MCOUNT_INSN_SIZE))
 105                 return -EPERM;
 106
 107         flush_icache_range(ip, ip + 8);
 108
 109         return 0;
 110 }
 111
 112 /*
 113  * Helper functions that are the same for both PPC64 and PPC32.
 114  */
 115 static int test_24bit_addr(unsigned long ip, unsigned long addr)
 116 {
 117
 118         /* use the create_branch to verify that this offset can be branched */
 119         return create_branch((unsigned int *)ip, addr, 0);
 120 }
 121
 122 static int is_bl_op(unsigned int op)
 123 {
 124         return (op & 0xfc000003) == 0x48000001;
 125 }
 126
 127 static unsigned long find_bl_target(unsigned long ip, unsigned int op)
 128 {
 129         static int offset;
 130
 131         offset = (op & 0x03fffffc);
 132         /* make it signed */
 133         if (offset & 0x02000000)
 134                 offset |= 0xfe000000;
 135
 136         return ip + (long)offset;
 137 }
 138
 139 #ifdef CONFIG_PPC64
 140 static int
 141 __ftrace_make_nop(struct module *mod,
 142                   struct dyn_ftrace *rec, unsigned long addr)
 143 {
 144         unsigned int op;
 145         unsigned int jmp[5];
 146         unsigned long ptr;
 147         unsigned long ip = rec->ip;
 148         unsigned long tramp;
 149         int offset;
 150
 151         /* read where this goes */
 152         if (probe_kernel_read(&op, (void *)ip, sizeof(int)))
 153                 return -EFAULT;
 154
 155         /* Make sure that that this is still a 24bit jump */
 156         if (!is_bl_op(op)) {
 157                 printk(KERN_ERR "Not expected bl: opcode is %x\n", op);
 158                 return -EINVAL;
 159         }
 160
 161         /* lets find where the pointer goes */
 162         tramp = find_bl_target(ip, op);
 163
 164         /*
 165          * On PPC64 the trampoline looks like:
 166          * 0x3d, 0x82, 0x00, 0x00,    addis   r12,r2, <high>
 167          * 0x39, 0x8c, 0x00, 0x00,    addi    r12,r12, <low>
 168          *   Where the bytes 2,3,6 and 7 make up the 32bit offset
 169          *   to the TOC that holds the pointer.
 170          *   to jump to.
 171          * 0xf8, 0x41, 0x00, 0x28,    std     r2,40(r1)
 172          * 0xe9, 0x6c, 0x00, 0x20,    ld      r11,32(r12)
 173          *   The actually address is 32 bytes from the offset
 174          *   into the TOC.
 175          * 0xe8, 0x4c, 0x00, 0x28,    ld      r2,40(r12)
 176          */
 177
 178         DEBUGP("ip:%lx jumps to %lx r2: %lx", ip, tramp, mod->arch.toc);
 179
 180         /* Find where the trampoline jumps to */
 181         if (probe_kernel_read(jmp, (void *)tramp, sizeof(jmp))) {
 182                 printk(KERN_ERR "Failed to read %lx\n", tramp);
 183                 return -EFAULT;
 184         }
 185
 186         DEBUGP(" %08x %08x", jmp[0], jmp[1]);
 187
 188         /* verify that this is what we expect it to be */
 189         if (((jmp[0] & 0xffff0000) != 0x3d820000) ||
 190             ((jmp[1] & 0xffff0000) != 0x398c0000) ||
 191             (jmp[2] != 0xf8410028) ||
 192             (jmp[3] != 0xe96c0020) ||
 193             (jmp[4] != 0xe84c0028)) {
 194                 printk(KERN_ERR "Not a trampoline\n");
 195                 return -EINVAL;
 196         }
 197
 198         offset = (unsigned)((unsigned short)jmp[0]) << 16 |
 199                 (unsigned)((unsigned short)jmp[1]);
 200
 201         DEBUGP(" %x ", offset);
 202
 203         /* get the address this jumps too */
 204         tramp = mod->arch.toc + offset + 32;
 205         DEBUGP("toc: %lx", tramp);
 206
 207         if (probe_kernel_read(jmp, (void *)tramp, 8)) {
 208                 printk(KERN_ERR "Failed to read %lx\n", tramp);
 209                 return -EFAULT;
 210         }
 211
 212         DEBUGP(" %08x %08x\n", jmp[0], jmp[1]);
 213
 214         ptr = ((unsigned long)jmp[0] << 32) + jmp[1];
 215
 216         /* This should match what was called */
 217         if (ptr != GET_ADDR(addr)) {
 218                 printk(KERN_ERR "addr does not match %lx\n", ptr);
 219                 return -EINVAL;
 220         }
 221
 222         /*
 223          * We want to nop the line, but the next line is
 224          *  0xe8, 0x41, 0x00, 0x28   ld r2,40(r1)
 225          * This needs to be turned to a nop too.
 226          */
 227         if (probe_kernel_read(&op, (void *)(ip+4), MCOUNT_INSN_SIZE))
 228                 return -EFAULT;
 229
 230         if (op != 0xe8410028) {
 231                 printk(KERN_ERR "Next line is not ld! (%08x)\n", op);
 232                 return -EINVAL;
 233         }
 234
 235         /*
 236          * Milton Miller pointed out that we can not blindly do nops.
 237          * If a task was preempted when calling a trace function,
 238          * the nops will remove the way to restore the TOC in r2
 239          * and the r2 TOC will get corrupted.
 240          */
 241
 242         /*
 243          * Replace:
 244          *   bl <tramp>  <==== will be replaced with "b 1f"
 245          *   ld r2,40(r1)
 246          *  1:
 247          */
 248         op = 0x48000008;        /* b +8 */
 249
 250         if (probe_kernel_write((void *)ip, &op, MCOUNT_INSN_SIZE))
 251                 return -EPERM;
 252
 253
 254         flush_icache_range(ip, ip + 8);
 255
 256         return 0;
 257 }
 258
 259 #else /* !PPC64 */
 260 static int
 261 __ftrace_make_nop(struct module *mod,
 262                   struct dyn_ftrace *rec, unsigned long addr)
 263 {
 264         unsigned int op;
 265         unsigned int jmp[4];
 266         unsigned long ip = rec->ip;
 267         unsigned long tramp;
 268
 269         if (probe_kernel_read(&op, (void *)ip, MCOUNT_INSN_SIZE))
 270                 return -EFAULT;
 271
 272         /* Make sure that that this is still a 24bit jump */
 273         if (!is_bl_op(op)) {
 274                 printk(KERN_ERR "Not expected bl: opcode is %x\n", op);
 275                 return -EINVAL;
 276         }
 277
 278         /* lets find where the pointer goes */
 279         tramp = find_bl_target(ip, op);
 280
 281         /*
 282          * On PPC32 the trampoline looks like:
 283          *  0x3d, 0x60, 0x00, 0x00  lis r11,sym@ha
 284          *  0x39, 0x6b, 0x00, 0x00  addi r11,r11,sym@l
 285          *  0x7d, 0x69, 0x03, 0xa6  mtctr r11
 286          *  0x4e, 0x80, 0x04, 0x20  bctr
 287          */
 288
 289         DEBUGP("ip:%lx jumps to %lx", ip, tramp);
 290
 291         /* Find where the trampoline jumps to */
 292         if (probe_kernel_read(jmp, (void *)tramp, sizeof(jmp))) {
 293                 printk(KERN_ERR "Failed to read %lx\n", tramp);
 294                 return -EFAULT;
 295         }
 296
 297         DEBUGP(" %08x %08x ", jmp[0], jmp[1]);
 298
 299         /* verify that this is what we expect it to be */
 300         if (((jmp[0] & 0xffff0000) != 0x3d600000) ||
 301             ((jmp[1] & 0xffff0000) != 0x396b0000) ||
 302             (jmp[2] != 0x7d6903a6) ||
 303             (jmp[3] != 0x4e800420)) {
 304                 printk(KERN_ERR "Not a trampoline\n");
 305                 return -EINVAL;
 306         }
 307
 308         tramp = (jmp[1] & 0xffff) |
 309                 ((jmp[0] & 0xffff) << 16);
 310         if (tramp & 0x8000)
 311                 tramp -= 0x10000;
 312
 313         DEBUGP(" %x ", tramp);
 314
 315         if (tramp != addr) {
 316                 printk(KERN_ERR
 317                        "Trampoline location %08lx does not match addr\n",
 318                        tramp);
 319                 return -EINVAL;
 320         }
 321
 322         op = PPC_NOP_INSTR;
 323
 324         if (probe_kernel_write((void *)ip, &op, MCOUNT_INSN_SIZE))
 325                 return -EPERM;
 326
 327         flush_icache_range(ip, ip + 8);
 328
 329         return 0;
 330 }
 331 #endif /* PPC64 */
 332
 333 int ftrace_make_nop(struct module *mod,
 334                     struct dyn_ftrace *rec, unsigned long addr)
 335 {
 336         unsigned char *old, *new;
 337         unsigned long ip = rec->ip;
 338
 339         /*
 340          * If the calling address is more that 24 bits away,
 341          * then we had to use a trampoline to make the call.
 342          * Otherwise just update the call site.
 343          */
 344         if (test_24bit_addr(ip, addr)) {
 345                 /* within range */
 346                 old = ftrace_call_replace(ip, addr);
 347                 new = ftrace_nop_replace();
 348                 return ftrace_modify_code(ip, old, new);
 349         }
 350
 351         /*
 352          * Out of range jumps are called from modules.
 353          * We should either already have a pointer to the module
 354          * or it has been passed in.
 355          */
 356         if (!rec->arch.mod) {
 357                 if (!mod) {
 358                         printk(KERN_ERR "No module loaded addr=%lx\n",
 359                                addr);
 360                         return -EFAULT;
 361                 }
 362                 rec->arch.mod = mod;
 363         } else if (mod) {
 364                 if (mod != rec->arch.mod) {
 365                         printk(KERN_ERR
 366                                "Record mod %p not equal to passed in mod %p\n",
 367                                rec->arch.mod, mod);
 368                         return -EINVAL;
 369                 }
 370                 /* nothing to do if mod == rec->arch.mod */
 371         } else
 372                 mod = rec->arch.mod;
 373
 374         return __ftrace_make_nop(mod, rec, addr);
 375
 376 }
 377
 378 #ifdef CONFIG_PPC64
 379 static int
 380 __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 381 {
 382         unsigned int op[2];
 383         unsigned long ip = rec->ip;
 384
 385         /* read where this goes */
 386         if (probe_kernel_read(op, (void *)ip, MCOUNT_INSN_SIZE * 2))
 387                 return -EFAULT;
 388
 389         /*
 390          * It should be pointing to two nops or
 391          *  b +8; ld r2,40(r1)
 392          */
 393         if (((op[0] != 0x48000008) || (op[1] != 0xe8410028)) &&
 394             ((op[0] != PPC_NOP_INSTR) || (op[1] != PPC_NOP_INSTR))) {
 395                 printk(KERN_ERR "Expected NOPs but have %x %x\n", op[0], op[1]);
 396                 return -EINVAL;
 397         }
 398
 399         /* If we never set up a trampoline to ftrace_caller, then bail */
 400         if (!rec->arch.mod->arch.tramp) {
 401                 printk(KERN_ERR "No ftrace trampoline\n");
 402                 return -EINVAL;
 403         }
 404
 405         /* create the branch to the trampoline */
 406         op[0] = create_branch((unsigned int *)ip,
 407                               rec->arch.mod->arch.tramp, BRANCH_SET_LINK);
 408         if (!op[0]) {
 409                 printk(KERN_ERR "REL24 out of range!\n");
 410                 return -EINVAL;
 411         }
 412
 413         /* ld r2,40(r1) */
 414         op[1] = 0xe8410028;
 415
 416         DEBUGP("write to %lx\n", rec->ip);
 417
 418         if (probe_kernel_write((void *)ip, op, MCOUNT_INSN_SIZE * 2))
 419                 return -EPERM;
 420
 421         flush_icache_range(ip, ip + 8);
 422
 423         return 0;
 424 }
 425 #else
 426 static int
 427 __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 428 {
 429         unsigned int op;
 430         unsigned long ip = rec->ip;
 431
 432         /* read where this goes */
 433         if (probe_kernel_read(&op, (void *)ip, MCOUNT_INSN_SIZE))
 434                 return -EFAULT;
 435
 436         /* It should be pointing to a nop */
 437         if (op != PPC_NOP_INSTR) {
 438                 printk(KERN_ERR "Expected NOP but have %x\n", op);
 439                 return -EINVAL;
 440         }
 441
 442         /* If we never set up a trampoline to ftrace_caller, then bail */
 443         if (!rec->arch.mod->arch.tramp) {
 444                 printk(KERN_ERR "No ftrace trampoline\n");
 445                 return -EINVAL;
 446         }
 447
 448         /* create the branch to the trampoline */
 449         op = create_branch((unsigned int *)ip,
 450                            rec->arch.mod->arch.tramp, BRANCH_SET_LINK);
 451         if (!op) {
 452                 printk(KERN_ERR "REL24 out of range!\n");
 453                 return -EINVAL;
 454         }
 455
 456         DEBUGP("write to %lx\n", rec->ip);
 457
 458         if (probe_kernel_write((void *)ip, &op, MCOUNT_INSN_SIZE))
 459                 return -EPERM;
 460
 461         flush_icache_range(ip, ip + 8);
 462
 463         return 0;
 464 }
 465 #endif /* CONFIG_PPC64 */
 466
 467 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 468 {
 469         unsigned char *old, *new;
 470         unsigned long ip = rec->ip;
 471
 472         /*
 473          * If the calling address is more that 24 bits away,
 474          * then we had to use a trampoline to make the call.
 475          * Otherwise just update the call site.
 476          */
 477         if (test_24bit_addr(ip, addr)) {
 478                 /* within range */
 479                 old = ftrace_nop_replace();
 480                 new = ftrace_call_replace(ip, addr);
 481                 return ftrace_modify_code(ip, old, new);
 482         }
 483
 484         /*
 485          * Out of range jumps are called from modules.
 486          * Being that we are converting from nop, it had better
 487          * already have a module defined.
 488          */
 489         if (!rec->arch.mod) {
 490                 printk(KERN_ERR "No module loaded\n");
 491                 return -EINVAL;
 492         }
 493
 494         return __ftrace_make_call(rec, addr);
 495 }
 496
 497 int ftrace_update_ftrace_func(ftrace_func_t func)
 498 {
 499         unsigned long ip = (unsigned long)(&ftrace_call);
 500         unsigned char old[MCOUNT_INSN_SIZE], *new;
 501         int ret;
 502
 503         memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
 504         new = ftrace_call_replace(ip, (unsigned long)func);
 505         ret = ftrace_modify_code(ip, old, new);
 506
 507         return ret;
 508 }
 509
 510 int __init ftrace_dyn_arch_init(void *data)
 511 {
 512         /* caller expects data to be zero */
 513         unsigned long *p = data;
 514
 515         *p = 0;
 516
 517         return 0;
 518 }