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         /* The bottom half is signed extended */
 199         offset = ((unsigned)((unsigned short)jmp[0]) << 16) +
 200                 (int)((short)jmp[1]);
 201
 202         DEBUGP(" %x ", offset);
 203
 204         /* get the address this jumps too */
 205         tramp = mod->arch.toc + offset + 32;
 206         DEBUGP("toc: %lx", tramp);
 207
 208         if (probe_kernel_read(jmp, (void *)tramp, 8)) {
 209                 printk(KERN_ERR "Failed to read %lx\n", tramp);
 210                 return -EFAULT;
 211         }
 212
 213         DEBUGP(" %08x %08x\n", jmp[0], jmp[1]);
 214
 215         ptr = ((unsigned long)jmp[0] << 32) + jmp[1];
 216
 217         /* This should match what was called */
 218         if (ptr != GET_ADDR(addr)) {
 219                 printk(KERN_ERR "addr does not match %lx\n", ptr);
 220                 return -EINVAL;
 221         }
 222
 223         /*
 224          * We want to nop the line, but the next line is
 225          *  0xe8, 0x41, 0x00, 0x28   ld r2,40(r1)
 226          * This needs to be turned to a nop too.
 227          */
 228         if (probe_kernel_read(&op, (void *)(ip+4), MCOUNT_INSN_SIZE))
 229                 return -EFAULT;
 230
 231         if (op != 0xe8410028) {
 232                 printk(KERN_ERR "Next line is not ld! (%08x)\n", op);
 233                 return -EINVAL;
 234         }
 235
 236         /*
 237          * Milton Miller pointed out that we can not blindly do nops.
 238          * If a task was preempted when calling a trace function,
 239          * the nops will remove the way to restore the TOC in r2
 240          * and the r2 TOC will get corrupted.
 241          */
 242
 243         /*
 244          * Replace:
 245          *   bl <tramp>  <==== will be replaced with "b 1f"
 246          *   ld r2,40(r1)
 247          *  1:
 248          */
 249         op = 0x48000008;        /* b +8 */
 250
 251         if (probe_kernel_write((void *)ip, &op, MCOUNT_INSN_SIZE))
 252                 return -EPERM;
 253
 254
 255         flush_icache_range(ip, ip + 8);
 256
 257         return 0;
 258 }
 259
 260 #else /* !PPC64 */
 261 static int
 262 __ftrace_make_nop(struct module *mod,
 263                   struct dyn_ftrace *rec, unsigned long addr)
 264 {
 265         unsigned int op;
 266         unsigned int jmp[4];
 267         unsigned long ip = rec->ip;
 268         unsigned long tramp;
 269
 270         if (probe_kernel_read(&op, (void *)ip, MCOUNT_INSN_SIZE))
 271                 return -EFAULT;
 272
 273         /* Make sure that that this is still a 24bit jump */
 274         if (!is_bl_op(op)) {
 275                 printk(KERN_ERR "Not expected bl: opcode is %x\n", op);
 276                 return -EINVAL;
 277         }
 278
 279         /* lets find where the pointer goes */
 280         tramp = find_bl_target(ip, op);
 281
 282         /*
 283          * On PPC32 the trampoline looks like:
 284          *  0x3d, 0x60, 0x00, 0x00  lis r11,sym@ha
 285          *  0x39, 0x6b, 0x00, 0x00  addi r11,r11,sym@l
 286          *  0x7d, 0x69, 0x03, 0xa6  mtctr r11
 287          *  0x4e, 0x80, 0x04, 0x20  bctr
 288          */
 289
 290         DEBUGP("ip:%lx jumps to %lx", ip, tramp);
 291
 292         /* Find where the trampoline jumps to */
 293         if (probe_kernel_read(jmp, (void *)tramp, sizeof(jmp))) {
 294                 printk(KERN_ERR "Failed to read %lx\n", tramp);
 295                 return -EFAULT;
 296         }
 297
 298         DEBUGP(" %08x %08x ", jmp[0], jmp[1]);
 299
 300         /* verify that this is what we expect it to be */
 301         if (((jmp[0] & 0xffff0000) != 0x3d600000) ||
 302             ((jmp[1] & 0xffff0000) != 0x396b0000) ||
 303             (jmp[2] != 0x7d6903a6) ||
 304             (jmp[3] != 0x4e800420)) {
 305                 printk(KERN_ERR "Not a trampoline\n");
 306                 return -EINVAL;
 307         }
 308
 309         tramp = (jmp[1] & 0xffff) |
 310                 ((jmp[0] & 0xffff) << 16);
 311         if (tramp & 0x8000)
 312                 tramp -= 0x10000;
 313
 314         DEBUGP(" %x ", tramp);
 315
 316         if (tramp != addr) {
 317                 printk(KERN_ERR
 318                        "Trampoline location %08lx does not match addr\n",
 319                        tramp);
 320                 return -EINVAL;
 321         }
 322
 323         op = PPC_NOP_INSTR;
 324
 325         if (probe_kernel_write((void *)ip, &op, MCOUNT_INSN_SIZE))
 326                 return -EPERM;
 327
 328         flush_icache_range(ip, ip + 8);
 329
 330         return 0;
 331 }
 332 #endif /* PPC64 */
 333
 334 int ftrace_make_nop(struct module *mod,
 335                     struct dyn_ftrace *rec, unsigned long addr)
 336 {
 337         unsigned char *old, *new;
 338         unsigned long ip = rec->ip;
 339
 340         /*
 341          * If the calling address is more that 24 bits away,
 342          * then we had to use a trampoline to make the call.
 343          * Otherwise just update the call site.
 344          */
 345         if (test_24bit_addr(ip, addr)) {
 346                 /* within range */
 347                 old = ftrace_call_replace(ip, addr);
 348                 new = ftrace_nop_replace();
 349                 return ftrace_modify_code(ip, old, new);
 350         }
 351
 352         /*
 353          * Out of range jumps are called from modules.
 354          * We should either already have a pointer to the module
 355          * or it has been passed in.
 356          */
 357         if (!rec->arch.mod) {
 358                 if (!mod) {
 359                         printk(KERN_ERR "No module loaded addr=%lx\n",
 360                                addr);
 361                         return -EFAULT;
 362                 }
 363                 rec->arch.mod = mod;
 364         } else if (mod) {
 365                 if (mod != rec->arch.mod) {
 366                         printk(KERN_ERR
 367                                "Record mod %p not equal to passed in mod %p\n",
 368                                rec->arch.mod, mod);
 369                         return -EINVAL;
 370                 }
 371                 /* nothing to do if mod == rec->arch.mod */
 372         } else
 373                 mod = rec->arch.mod;
 374
 375         return __ftrace_make_nop(mod, rec, addr);
 376
 377 }
 378
 379 #ifdef CONFIG_PPC64
 380 static int
 381 __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 382 {
 383         unsigned int op[2];
 384         unsigned long ip = rec->ip;
 385
 386         /* read where this goes */
 387         if (probe_kernel_read(op, (void *)ip, MCOUNT_INSN_SIZE * 2))
 388                 return -EFAULT;
 389
 390         /*
 391          * It should be pointing to two nops or
 392          *  b +8; ld r2,40(r1)
 393          */
 394         if (((op[0] != 0x48000008) || (op[1] != 0xe8410028)) &&
 395             ((op[0] != PPC_NOP_INSTR) || (op[1] != PPC_NOP_INSTR))) {
 396                 printk(KERN_ERR "Expected NOPs but have %x %x\n", op[0], op[1]);
 397                 return -EINVAL;
 398         }
 399
 400         /* If we never set up a trampoline to ftrace_caller, then bail */
 401         if (!rec->arch.mod->arch.tramp) {
 402                 printk(KERN_ERR "No ftrace trampoline\n");
 403                 return -EINVAL;
 404         }
 405
 406         /* create the branch to the trampoline */
 407         op[0] = create_branch((unsigned int *)ip,
 408                               rec->arch.mod->arch.tramp, BRANCH_SET_LINK);
 409         if (!op[0]) {
 410                 printk(KERN_ERR "REL24 out of range!\n");
 411                 return -EINVAL;
 412         }
 413
 414         /* ld r2,40(r1) */
 415         op[1] = 0xe8410028;
 416
 417         DEBUGP("write to %lx\n", rec->ip);
 418
 419         if (probe_kernel_write((void *)ip, op, MCOUNT_INSN_SIZE * 2))
 420                 return -EPERM;
 421
 422         flush_icache_range(ip, ip + 8);
 423
 424         return 0;
 425 }
 426 #else
 427 static int
 428 __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 429 {
 430         unsigned int op;
 431         unsigned long ip = rec->ip;
 432
 433         /* read where this goes */
 434         if (probe_kernel_read(&op, (void *)ip, MCOUNT_INSN_SIZE))
 435                 return -EFAULT;
 436
 437         /* It should be pointing to a nop */
 438         if (op != PPC_NOP_INSTR) {
 439                 printk(KERN_ERR "Expected NOP but have %x\n", op);
 440                 return -EINVAL;
 441         }
 442
 443         /* If we never set up a trampoline to ftrace_caller, then bail */
 444         if (!rec->arch.mod->arch.tramp) {
 445                 printk(KERN_ERR "No ftrace trampoline\n");
 446                 return -EINVAL;
 447         }
 448
 449         /* create the branch to the trampoline */
 450         op = create_branch((unsigned int *)ip,
 451                            rec->arch.mod->arch.tramp, BRANCH_SET_LINK);
 452         if (!op) {
 453                 printk(KERN_ERR "REL24 out of range!\n");
 454                 return -EINVAL;
 455         }
 456
 457         DEBUGP("write to %lx\n", rec->ip);
 458
 459         if (probe_kernel_write((void *)ip, &op, MCOUNT_INSN_SIZE))
 460                 return -EPERM;
 461
 462         flush_icache_range(ip, ip + 8);
 463
 464         return 0;
 465 }
 466 #endif /* CONFIG_PPC64 */
 467
 468 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 469 {
 470         unsigned char *old, *new;
 471         unsigned long ip = rec->ip;
 472
 473         /*
 474          * If the calling address is more that 24 bits away,
 475          * then we had to use a trampoline to make the call.
 476          * Otherwise just update the call site.
 477          */
 478         if (test_24bit_addr(ip, addr)) {
 479                 /* within range */
 480                 old = ftrace_nop_replace();
 481                 new = ftrace_call_replace(ip, addr);
 482                 return ftrace_modify_code(ip, old, new);
 483         }
 484
 485         /*
 486          * Out of range jumps are called from modules.
 487          * Being that we are converting from nop, it had better
 488          * already have a module defined.
 489          */
 490         if (!rec->arch.mod) {
 491                 printk(KERN_ERR "No module loaded\n");
 492                 return -EINVAL;
 493         }
 494
 495         return __ftrace_make_call(rec, addr);
 496 }
 497
 498 int ftrace_update_ftrace_func(ftrace_func_t func)
 499 {
 500         unsigned long ip = (unsigned long)(&ftrace_call);
 501         unsigned char old[MCOUNT_INSN_SIZE], *new;
 502         int ret;
 503
 504         memcpy(old, &ftrace_call, MCOUNT_INSN_SIZE);
 505         new = ftrace_call_replace(ip, (unsigned long)func);
 506         ret = ftrace_modify_code(ip, old, new);
 507
 508         return ret;
 509 }
 510
 511 int __init ftrace_dyn_arch_init(void *data)
 512 {
 513         /* caller expects data to be zero */
 514         unsigned long *p = data;
 515
 516         *p = 0;
 517
 518         return 0;
 519 }