linux/arch/powerpc/lib/code-patching.c
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   1/*
   2 *  Copyright 2008 Michael Ellerman, IBM Corporation.
   3 *
   4 *  This program is free software; you can redistribute it and/or
   5 *  modify it under the terms of the GNU General Public License
   6 *  as published by the Free Software Foundation; either version
   7 *  2 of the License, or (at your option) any later version.
   8 */
   9
  10#include <linux/kernel.h>
  11#include <linux/vmalloc.h>
  12#include <linux/init.h>
  13#include <linux/mm.h>
  14#include <asm/page.h>
  15#include <asm/code-patching.h>
  16#include <asm/uaccess.h>
  17
  18
  19int patch_instruction(unsigned int *addr, unsigned int instr)
  20{
  21        int err;
  22
  23        __put_user_size(instr, addr, 4, err);
  24        if (err)
  25                return err;
  26        asm ("dcbst 0, %0; sync; icbi 0,%0; sync; isync" : : "r" (addr));
  27        return 0;
  28}
  29
  30int patch_branch(unsigned int *addr, unsigned long target, int flags)
  31{
  32        return patch_instruction(addr, create_branch(addr, target, flags));
  33}
  34
  35unsigned int create_branch(const unsigned int *addr,
  36                           unsigned long target, int flags)
  37{
  38        unsigned int instruction;
  39        long offset;
  40
  41        offset = target;
  42        if (! (flags & BRANCH_ABSOLUTE))
  43                offset = offset - (unsigned long)addr;
  44
  45        /* Check we can represent the target in the instruction format */
  46        if (offset < -0x2000000 || offset > 0x1fffffc || offset & 0x3)
  47                return 0;
  48
  49        /* Mask out the flags and target, so they don't step on each other. */
  50        instruction = 0x48000000 | (flags & 0x3) | (offset & 0x03FFFFFC);
  51
  52        return instruction;
  53}
  54
  55unsigned int create_cond_branch(const unsigned int *addr,
  56                                unsigned long target, int flags)
  57{
  58        unsigned int instruction;
  59        long offset;
  60
  61        offset = target;
  62        if (! (flags & BRANCH_ABSOLUTE))
  63                offset = offset - (unsigned long)addr;
  64
  65        /* Check we can represent the target in the instruction format */
  66        if (offset < -0x8000 || offset > 0x7FFF || offset & 0x3)
  67                return 0;
  68
  69        /* Mask out the flags and target, so they don't step on each other. */
  70        instruction = 0x40000000 | (flags & 0x3FF0003) | (offset & 0xFFFC);
  71
  72        return instruction;
  73}
  74
  75static unsigned int branch_opcode(unsigned int instr)
  76{
  77        return (instr >> 26) & 0x3F;
  78}
  79
  80static int instr_is_branch_iform(unsigned int instr)
  81{
  82        return branch_opcode(instr) == 18;
  83}
  84
  85static int instr_is_branch_bform(unsigned int instr)
  86{
  87        return branch_opcode(instr) == 16;
  88}
  89
  90int instr_is_relative_branch(unsigned int instr)
  91{
  92        if (instr & BRANCH_ABSOLUTE)
  93                return 0;
  94
  95        return instr_is_branch_iform(instr) || instr_is_branch_bform(instr);
  96}
  97
  98static unsigned long branch_iform_target(const unsigned int *instr)
  99{
 100        signed long imm;
 101
 102        imm = *instr & 0x3FFFFFC;
 103
 104        /* If the top bit of the immediate value is set this is negative */
 105        if (imm & 0x2000000)
 106                imm -= 0x4000000;
 107
 108        if ((*instr & BRANCH_ABSOLUTE) == 0)
 109                imm += (unsigned long)instr;
 110
 111        return (unsigned long)imm;
 112}
 113
 114static unsigned long branch_bform_target(const unsigned int *instr)
 115{
 116        signed long imm;
 117
 118        imm = *instr & 0xFFFC;
 119
 120        /* If the top bit of the immediate value is set this is negative */
 121        if (imm & 0x8000)
 122                imm -= 0x10000;
 123
 124        if ((*instr & BRANCH_ABSOLUTE) == 0)
 125                imm += (unsigned long)instr;
 126
 127        return (unsigned long)imm;
 128}
 129
 130unsigned long branch_target(const unsigned int *instr)
 131{
 132        if (instr_is_branch_iform(*instr))
 133                return branch_iform_target(instr);
 134        else if (instr_is_branch_bform(*instr))
 135                return branch_bform_target(instr);
 136
 137        return 0;
 138}
 139
 140int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr)
 141{
 142        if (instr_is_branch_iform(*instr) || instr_is_branch_bform(*instr))
 143                return branch_target(instr) == addr;
 144
 145        return 0;
 146}
 147
 148unsigned int translate_branch(const unsigned int *dest, const unsigned int *src)
 149{
 150        unsigned long target;
 151
 152        target = branch_target(src);
 153
 154        if (instr_is_branch_iform(*src))
 155                return create_branch(dest, target, *src);
 156        else if (instr_is_branch_bform(*src))
 157                return create_cond_branch(dest, target, *src);
 158
 159        return 0;
 160}
 161
 162
 163#ifdef CONFIG_CODE_PATCHING_SELFTEST
 164
 165static void __init test_trampoline(void)
 166{
 167        asm ("nop;\n");
 168}
 169
 170#define check(x)        \
 171        if (!(x)) printk("code-patching: test failed at line %d\n", __LINE__);
 172
 173static void __init test_branch_iform(void)
 174{
 175        unsigned int instr;
 176        unsigned long addr;
 177
 178        addr = (unsigned long)&instr;
 179
 180        /* The simplest case, branch to self, no flags */
 181        check(instr_is_branch_iform(0x48000000));
 182        /* All bits of target set, and flags */
 183        check(instr_is_branch_iform(0x4bffffff));
 184        /* High bit of opcode set, which is wrong */
 185        check(!instr_is_branch_iform(0xcbffffff));
 186        /* Middle bits of opcode set, which is wrong */
 187        check(!instr_is_branch_iform(0x7bffffff));
 188
 189        /* Simplest case, branch to self with link */
 190        check(instr_is_branch_iform(0x48000001));
 191        /* All bits of targets set */
 192        check(instr_is_branch_iform(0x4bfffffd));
 193        /* Some bits of targets set */
 194        check(instr_is_branch_iform(0x4bff00fd));
 195        /* Must be a valid branch to start with */
 196        check(!instr_is_branch_iform(0x7bfffffd));
 197
 198        /* Absolute branch to 0x100 */
 199        instr = 0x48000103;
 200        check(instr_is_branch_to_addr(&instr, 0x100));
 201        /* Absolute branch to 0x420fc */
 202        instr = 0x480420ff;
 203        check(instr_is_branch_to_addr(&instr, 0x420fc));
 204        /* Maximum positive relative branch, + 20MB - 4B */
 205        instr = 0x49fffffc;
 206        check(instr_is_branch_to_addr(&instr, addr + 0x1FFFFFC));
 207        /* Smallest negative relative branch, - 4B */
 208        instr = 0x4bfffffc;
 209        check(instr_is_branch_to_addr(&instr, addr - 4));
 210        /* Largest negative relative branch, - 32 MB */
 211        instr = 0x4a000000;
 212        check(instr_is_branch_to_addr(&instr, addr - 0x2000000));
 213
 214        /* Branch to self, with link */
 215        instr = create_branch(&instr, addr, BRANCH_SET_LINK);
 216        check(instr_is_branch_to_addr(&instr, addr));
 217
 218        /* Branch to self - 0x100, with link */
 219        instr = create_branch(&instr, addr - 0x100, BRANCH_SET_LINK);
 220        check(instr_is_branch_to_addr(&instr, addr - 0x100));
 221
 222        /* Branch to self + 0x100, no link */
 223        instr = create_branch(&instr, addr + 0x100, 0);
 224        check(instr_is_branch_to_addr(&instr, addr + 0x100));
 225
 226        /* Maximum relative negative offset, - 32 MB */
 227        instr = create_branch(&instr, addr - 0x2000000, BRANCH_SET_LINK);
 228        check(instr_is_branch_to_addr(&instr, addr - 0x2000000));
 229
 230        /* Out of range relative negative offset, - 32 MB + 4*/
 231        instr = create_branch(&instr, addr - 0x2000004, BRANCH_SET_LINK);
 232        check(instr == 0);
 233
 234        /* Out of range relative positive offset, + 32 MB */
 235        instr = create_branch(&instr, addr + 0x2000000, BRANCH_SET_LINK);
 236        check(instr == 0);
 237
 238        /* Unaligned target */
 239        instr = create_branch(&instr, addr + 3, BRANCH_SET_LINK);
 240        check(instr == 0);
 241
 242        /* Check flags are masked correctly */
 243        instr = create_branch(&instr, addr, 0xFFFFFFFC);
 244        check(instr_is_branch_to_addr(&instr, addr));
 245        check(instr == 0x48000000);
 246}
 247
 248static void __init test_create_function_call(void)
 249{
 250        unsigned int *iptr;
 251        unsigned long dest;
 252
 253        /* Check we can create a function call */
 254        iptr = (unsigned int *)ppc_function_entry(test_trampoline);
 255        dest = ppc_function_entry(test_create_function_call);
 256        patch_instruction(iptr, create_branch(iptr, dest, BRANCH_SET_LINK));
 257        check(instr_is_branch_to_addr(iptr, dest));
 258}
 259
 260static void __init test_branch_bform(void)
 261{
 262        unsigned long addr;
 263        unsigned int *iptr, instr, flags;
 264
 265        iptr = &instr;
 266        addr = (unsigned long)iptr;
 267
 268        /* The simplest case, branch to self, no flags */
 269        check(instr_is_branch_bform(0x40000000));
 270        /* All bits of target set, and flags */
 271        check(instr_is_branch_bform(0x43ffffff));
 272        /* High bit of opcode set, which is wrong */
 273        check(!instr_is_branch_bform(0xc3ffffff));
 274        /* Middle bits of opcode set, which is wrong */
 275        check(!instr_is_branch_bform(0x7bffffff));
 276
 277        /* Absolute conditional branch to 0x100 */
 278        instr = 0x43ff0103;
 279        check(instr_is_branch_to_addr(&instr, 0x100));
 280        /* Absolute conditional branch to 0x20fc */
 281        instr = 0x43ff20ff;
 282        check(instr_is_branch_to_addr(&instr, 0x20fc));
 283        /* Maximum positive relative conditional branch, + 32 KB - 4B */
 284        instr = 0x43ff7ffc;
 285        check(instr_is_branch_to_addr(&instr, addr + 0x7FFC));
 286        /* Smallest negative relative conditional branch, - 4B */
 287        instr = 0x43fffffc;
 288        check(instr_is_branch_to_addr(&instr, addr - 4));
 289        /* Largest negative relative conditional branch, - 32 KB */
 290        instr = 0x43ff8000;
 291        check(instr_is_branch_to_addr(&instr, addr - 0x8000));
 292
 293        /* All condition code bits set & link */
 294        flags = 0x3ff000 | BRANCH_SET_LINK;
 295
 296        /* Branch to self */
 297        instr = create_cond_branch(iptr, addr, flags);
 298        check(instr_is_branch_to_addr(&instr, addr));
 299
 300        /* Branch to self - 0x100 */
 301        instr = create_cond_branch(iptr, addr - 0x100, flags);
 302        check(instr_is_branch_to_addr(&instr, addr - 0x100));
 303
 304        /* Branch to self + 0x100 */
 305        instr = create_cond_branch(iptr, addr + 0x100, flags);
 306        check(instr_is_branch_to_addr(&instr, addr + 0x100));
 307
 308        /* Maximum relative negative offset, - 32 KB */
 309        instr = create_cond_branch(iptr, addr - 0x8000, flags);
 310        check(instr_is_branch_to_addr(&instr, addr - 0x8000));
 311
 312        /* Out of range relative negative offset, - 32 KB + 4*/
 313        instr = create_cond_branch(iptr, addr - 0x8004, flags);
 314        check(instr == 0);
 315
 316        /* Out of range relative positive offset, + 32 KB */
 317        instr = create_cond_branch(iptr, addr + 0x8000, flags);
 318        check(instr == 0);
 319
 320        /* Unaligned target */
 321        instr = create_cond_branch(iptr, addr + 3, flags);
 322        check(instr == 0);
 323
 324        /* Check flags are masked correctly */
 325        instr = create_cond_branch(iptr, addr, 0xFFFFFFFC);
 326        check(instr_is_branch_to_addr(&instr, addr));
 327        check(instr == 0x43FF0000);
 328}
 329
 330static void __init test_translate_branch(void)
 331{
 332        unsigned long addr;
 333        unsigned int *p, *q;
 334        void *buf;
 335
 336        buf = vmalloc(PAGE_ALIGN(0x2000000 + 1));
 337        check(buf);
 338        if (!buf)
 339                return;
 340
 341        /* Simple case, branch to self moved a little */
 342        p = buf;
 343        addr = (unsigned long)p;
 344        patch_branch(p, addr, 0);
 345        check(instr_is_branch_to_addr(p, addr));
 346        q = p + 1;
 347        patch_instruction(q, translate_branch(q, p));
 348        check(instr_is_branch_to_addr(q, addr));
 349
 350        /* Maximum negative case, move b . to addr + 32 MB */
 351        p = buf;
 352        addr = (unsigned long)p;
 353        patch_branch(p, addr, 0);
 354        q = buf + 0x2000000;
 355        patch_instruction(q, translate_branch(q, p));
 356        check(instr_is_branch_to_addr(p, addr));
 357        check(instr_is_branch_to_addr(q, addr));
 358        check(*q == 0x4a000000);
 359
 360        /* Maximum positive case, move x to x - 32 MB + 4 */
 361        p = buf + 0x2000000;
 362        addr = (unsigned long)p;
 363        patch_branch(p, addr, 0);
 364        q = buf + 4;
 365        patch_instruction(q, translate_branch(q, p));
 366        check(instr_is_branch_to_addr(p, addr));
 367        check(instr_is_branch_to_addr(q, addr));
 368        check(*q == 0x49fffffc);
 369
 370        /* Jump to x + 16 MB moved to x + 20 MB */
 371        p = buf;
 372        addr = 0x1000000 + (unsigned long)buf;
 373        patch_branch(p, addr, BRANCH_SET_LINK);
 374        q = buf + 0x1400000;
 375        patch_instruction(q, translate_branch(q, p));
 376        check(instr_is_branch_to_addr(p, addr));
 377        check(instr_is_branch_to_addr(q, addr));
 378
 379        /* Jump to x + 16 MB moved to x - 16 MB + 4 */
 380        p = buf + 0x1000000;
 381        addr = 0x2000000 + (unsigned long)buf;
 382        patch_branch(p, addr, 0);
 383        q = buf + 4;
 384        patch_instruction(q, translate_branch(q, p));
 385        check(instr_is_branch_to_addr(p, addr));
 386        check(instr_is_branch_to_addr(q, addr));
 387
 388
 389        /* Conditional branch tests */
 390
 391        /* Simple case, branch to self moved a little */
 392        p = buf;
 393        addr = (unsigned long)p;
 394        patch_instruction(p, create_cond_branch(p, addr, 0));
 395        check(instr_is_branch_to_addr(p, addr));
 396        q = p + 1;
 397        patch_instruction(q, translate_branch(q, p));
 398        check(instr_is_branch_to_addr(q, addr));
 399
 400        /* Maximum negative case, move b . to addr + 32 KB */
 401        p = buf;
 402        addr = (unsigned long)p;
 403        patch_instruction(p, create_cond_branch(p, addr, 0xFFFFFFFC));
 404        q = buf + 0x8000;
 405        patch_instruction(q, translate_branch(q, p));
 406        check(instr_is_branch_to_addr(p, addr));
 407        check(instr_is_branch_to_addr(q, addr));
 408        check(*q == 0x43ff8000);
 409
 410        /* Maximum positive case, move x to x - 32 KB + 4 */
 411        p = buf + 0x8000;
 412        addr = (unsigned long)p;
 413        patch_instruction(p, create_cond_branch(p, addr, 0xFFFFFFFC));
 414        q = buf + 4;
 415        patch_instruction(q, translate_branch(q, p));
 416        check(instr_is_branch_to_addr(p, addr));
 417        check(instr_is_branch_to_addr(q, addr));
 418        check(*q == 0x43ff7ffc);
 419
 420        /* Jump to x + 12 KB moved to x + 20 KB */
 421        p = buf;
 422        addr = 0x3000 + (unsigned long)buf;
 423        patch_instruction(p, create_cond_branch(p, addr, BRANCH_SET_LINK));
 424        q = buf + 0x5000;
 425        patch_instruction(q, translate_branch(q, p));
 426        check(instr_is_branch_to_addr(p, addr));
 427        check(instr_is_branch_to_addr(q, addr));
 428
 429        /* Jump to x + 8 KB moved to x - 8 KB + 4 */
 430        p = buf + 0x2000;
 431        addr = 0x4000 + (unsigned long)buf;
 432        patch_instruction(p, create_cond_branch(p, addr, 0));
 433        q = buf + 4;
 434        patch_instruction(q, translate_branch(q, p));
 435        check(instr_is_branch_to_addr(p, addr));
 436        check(instr_is_branch_to_addr(q, addr));
 437
 438        /* Free the buffer we were using */
 439        vfree(buf);
 440}
 441
 442static int __init test_code_patching(void)
 443{
 444        printk(KERN_DEBUG "Running code patching self-tests ...\n");
 445
 446        test_branch_iform();
 447        test_branch_bform();
 448        test_create_function_call();
 449        test_translate_branch();
 450
 451        return 0;
 452}
 453late_initcall(test_code_patching);
 454
 455#endif /* CONFIG_CODE_PATCHING_SELFTEST */
 456