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code-patching.c

/*
 *  Copyright 2008 Michael Ellerman, IBM Corporation.
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 */

#include <linux/kernel.h>
#include <linux/vmalloc.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <asm/page.h>
#include <asm/code-patching.h>


void patch_instruction(unsigned int *addr, unsigned int instr)
{
      *addr = instr;
      asm ("dcbst 0, %0; sync; icbi 0,%0; sync; isync" : : "r" (addr));
}

void patch_branch(unsigned int *addr, unsigned long target, int flags)
{
      patch_instruction(addr, create_branch(addr, target, flags));
}

unsigned int create_branch(const unsigned int *addr,
                     unsigned long target, int flags)
{
      unsigned int instruction;
      long offset;

      offset = target;
      if (! (flags & BRANCH_ABSOLUTE))
            offset = offset - (unsigned long)addr;

      /* Check we can represent the target in the instruction format */
      if (offset < -0x2000000 || offset > 0x1fffffc || offset & 0x3)
            return 0;

      /* Mask out the flags and target, so they don't step on each other. */
      instruction = 0x48000000 | (flags & 0x3) | (offset & 0x03FFFFFC);

      return instruction;
}

unsigned int create_cond_branch(const unsigned int *addr,
                        unsigned long target, int flags)
{
      unsigned int instruction;
      long offset;

      offset = target;
      if (! (flags & BRANCH_ABSOLUTE))
            offset = offset - (unsigned long)addr;

      /* Check we can represent the target in the instruction format */
      if (offset < -0x8000 || offset > 0x7FFF || offset & 0x3)
            return 0;

      /* Mask out the flags and target, so they don't step on each other. */
      instruction = 0x40000000 | (flags & 0x3FF0003) | (offset & 0xFFFC);

      return instruction;
}

static unsigned int branch_opcode(unsigned int instr)
{
      return (instr >> 26) & 0x3F;
}

static int instr_is_branch_iform(unsigned int instr)
{
      return branch_opcode(instr) == 18;
}

static int instr_is_branch_bform(unsigned int instr)
{
      return branch_opcode(instr) == 16;
}

int instr_is_relative_branch(unsigned int instr)
{
      if (instr & BRANCH_ABSOLUTE)
            return 0;

      return instr_is_branch_iform(instr) || instr_is_branch_bform(instr);
}

static unsigned long branch_iform_target(const unsigned int *instr)
{
      signed long imm;

      imm = *instr & 0x3FFFFFC;

      /* If the top bit of the immediate value is set this is negative */
      if (imm & 0x2000000)
            imm -= 0x4000000;

      if ((*instr & BRANCH_ABSOLUTE) == 0)
            imm += (unsigned long)instr;

      return (unsigned long)imm;
}

static unsigned long branch_bform_target(const unsigned int *instr)
{
      signed long imm;

      imm = *instr & 0xFFFC;

      /* If the top bit of the immediate value is set this is negative */
      if (imm & 0x8000)
            imm -= 0x10000;

      if ((*instr & BRANCH_ABSOLUTE) == 0)
            imm += (unsigned long)instr;

      return (unsigned long)imm;
}

unsigned long branch_target(const unsigned int *instr)
{
      if (instr_is_branch_iform(*instr))
            return branch_iform_target(instr);
      else if (instr_is_branch_bform(*instr))
            return branch_bform_target(instr);

      return 0;
}

int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr)
{
      if (instr_is_branch_iform(*instr) || instr_is_branch_bform(*instr))
            return branch_target(instr) == addr;

      return 0;
}

unsigned int translate_branch(const unsigned int *dest, const unsigned int *src)
{
      unsigned long target;

      target = branch_target(src);

      if (instr_is_branch_iform(*src))
            return create_branch(dest, target, *src);
      else if (instr_is_branch_bform(*src))
            return create_cond_branch(dest, target, *src);

      return 0;
}


#ifdef CONFIG_CODE_PATCHING_SELFTEST

static void __init test_trampoline(void)
{
      asm ("nop;\n");
}

#define check(x)  \
      if (!(x)) printk("code-patching: test failed at line %d\n", __LINE__);

static void __init test_branch_iform(void)
{
      unsigned int instr;
      unsigned long addr;

      addr = (unsigned long)&instr;

      /* The simplest case, branch to self, no flags */
      check(instr_is_branch_iform(0x48000000));
      /* All bits of target set, and flags */
      check(instr_is_branch_iform(0x4bffffff));
      /* High bit of opcode set, which is wrong */
      check(!instr_is_branch_iform(0xcbffffff));
      /* Middle bits of opcode set, which is wrong */
      check(!instr_is_branch_iform(0x7bffffff));

      /* Simplest case, branch to self with link */
      check(instr_is_branch_iform(0x48000001));
      /* All bits of targets set */
      check(instr_is_branch_iform(0x4bfffffd));
      /* Some bits of targets set */
      check(instr_is_branch_iform(0x4bff00fd));
      /* Must be a valid branch to start with */
      check(!instr_is_branch_iform(0x7bfffffd));

      /* Absolute branch to 0x100 */
      instr = 0x48000103;
      check(instr_is_branch_to_addr(&instr, 0x100));
      /* Absolute branch to 0x420fc */
      instr = 0x480420ff;
      check(instr_is_branch_to_addr(&instr, 0x420fc));
      /* Maximum positive relative branch, + 20MB - 4B */
      instr = 0x49fffffc;
      check(instr_is_branch_to_addr(&instr, addr + 0x1FFFFFC));
      /* Smallest negative relative branch, - 4B */
      instr = 0x4bfffffc;
      check(instr_is_branch_to_addr(&instr, addr - 4));
      /* Largest negative relative branch, - 32 MB */
      instr = 0x4a000000;
      check(instr_is_branch_to_addr(&instr, addr - 0x2000000));

      /* Branch to self, with link */
      instr = create_branch(&instr, addr, BRANCH_SET_LINK);
      check(instr_is_branch_to_addr(&instr, addr));

      /* Branch to self - 0x100, with link */
      instr = create_branch(&instr, addr - 0x100, BRANCH_SET_LINK);
      check(instr_is_branch_to_addr(&instr, addr - 0x100));

      /* Branch to self + 0x100, no link */
      instr = create_branch(&instr, addr + 0x100, 0);
      check(instr_is_branch_to_addr(&instr, addr + 0x100));

      /* Maximum relative negative offset, - 32 MB */
      instr = create_branch(&instr, addr - 0x2000000, BRANCH_SET_LINK);
      check(instr_is_branch_to_addr(&instr, addr - 0x2000000));

      /* Out of range relative negative offset, - 32 MB + 4*/
      instr = create_branch(&instr, addr - 0x2000004, BRANCH_SET_LINK);
      check(instr == 0);

      /* Out of range relative positive offset, + 32 MB */
      instr = create_branch(&instr, addr + 0x2000000, BRANCH_SET_LINK);
      check(instr == 0);

      /* Unaligned target */
      instr = create_branch(&instr, addr + 3, BRANCH_SET_LINK);
      check(instr == 0);

      /* Check flags are masked correctly */
      instr = create_branch(&instr, addr, 0xFFFFFFFC);
      check(instr_is_branch_to_addr(&instr, addr));
      check(instr == 0x48000000);
}

static void __init test_create_function_call(void)
{
      unsigned int *iptr;
      unsigned long dest;

      /* Check we can create a function call */
      iptr = (unsigned int *)ppc_function_entry(test_trampoline);
      dest = ppc_function_entry(test_create_function_call);
      patch_instruction(iptr, create_branch(iptr, dest, BRANCH_SET_LINK));
      check(instr_is_branch_to_addr(iptr, dest));
}

static void __init test_branch_bform(void)
{
      unsigned long addr;
      unsigned int *iptr, instr, flags;

      iptr = &instr;
      addr = (unsigned long)iptr;

      /* The simplest case, branch to self, no flags */
      check(instr_is_branch_bform(0x40000000));
      /* All bits of target set, and flags */
      check(instr_is_branch_bform(0x43ffffff));
      /* High bit of opcode set, which is wrong */
      check(!instr_is_branch_bform(0xc3ffffff));
      /* Middle bits of opcode set, which is wrong */
      check(!instr_is_branch_bform(0x7bffffff));

      /* Absolute conditional branch to 0x100 */
      instr = 0x43ff0103;
      check(instr_is_branch_to_addr(&instr, 0x100));
      /* Absolute conditional branch to 0x20fc */
      instr = 0x43ff20ff;
      check(instr_is_branch_to_addr(&instr, 0x20fc));
      /* Maximum positive relative conditional branch, + 32 KB - 4B */
      instr = 0x43ff7ffc;
      check(instr_is_branch_to_addr(&instr, addr + 0x7FFC));
      /* Smallest negative relative conditional branch, - 4B */
      instr = 0x43fffffc;
      check(instr_is_branch_to_addr(&instr, addr - 4));
      /* Largest negative relative conditional branch, - 32 KB */
      instr = 0x43ff8000;
      check(instr_is_branch_to_addr(&instr, addr - 0x8000));

      /* All condition code bits set & link */
      flags = 0x3ff000 | BRANCH_SET_LINK;

      /* Branch to self */
      instr = create_cond_branch(iptr, addr, flags);
      check(instr_is_branch_to_addr(&instr, addr));

      /* Branch to self - 0x100 */
      instr = create_cond_branch(iptr, addr - 0x100, flags);
      check(instr_is_branch_to_addr(&instr, addr - 0x100));

      /* Branch to self + 0x100 */
      instr = create_cond_branch(iptr, addr + 0x100, flags);
      check(instr_is_branch_to_addr(&instr, addr + 0x100));

      /* Maximum relative negative offset, - 32 KB */
      instr = create_cond_branch(iptr, addr - 0x8000, flags);
      check(instr_is_branch_to_addr(&instr, addr - 0x8000));

      /* Out of range relative negative offset, - 32 KB + 4*/
      instr = create_cond_branch(iptr, addr - 0x8004, flags);
      check(instr == 0);

      /* Out of range relative positive offset, + 32 KB */
      instr = create_cond_branch(iptr, addr + 0x8000, flags);
      check(instr == 0);

      /* Unaligned target */
      instr = create_cond_branch(iptr, addr + 3, flags);
      check(instr == 0);

      /* Check flags are masked correctly */
      instr = create_cond_branch(iptr, addr, 0xFFFFFFFC);
      check(instr_is_branch_to_addr(&instr, addr));
      check(instr == 0x43FF0000);
}

static void __init test_translate_branch(void)
{
      unsigned long addr;
      unsigned int *p, *q;
      void *buf;

      buf = vmalloc(PAGE_ALIGN(0x2000000 + 1));
      check(buf);
      if (!buf)
            return;

      /* Simple case, branch to self moved a little */
      p = buf;
      addr = (unsigned long)p;
      patch_branch(p, addr, 0);
      check(instr_is_branch_to_addr(p, addr));
      q = p + 1;
      patch_instruction(q, translate_branch(q, p));
      check(instr_is_branch_to_addr(q, addr));

      /* Maximum negative case, move b . to addr + 32 MB */
      p = buf;
      addr = (unsigned long)p;
      patch_branch(p, addr, 0);
      q = buf + 0x2000000;
      patch_instruction(q, translate_branch(q, p));
      check(instr_is_branch_to_addr(p, addr));
      check(instr_is_branch_to_addr(q, addr));
      check(*q == 0x4a000000);

      /* Maximum positive case, move x to x - 32 MB + 4 */
      p = buf + 0x2000000;
      addr = (unsigned long)p;
      patch_branch(p, addr, 0);
      q = buf + 4;
      patch_instruction(q, translate_branch(q, p));
      check(instr_is_branch_to_addr(p, addr));
      check(instr_is_branch_to_addr(q, addr));
      check(*q == 0x49fffffc);

      /* Jump to x + 16 MB moved to x + 20 MB */
      p = buf;
      addr = 0x1000000 + (unsigned long)buf;
      patch_branch(p, addr, BRANCH_SET_LINK);
      q = buf + 0x1400000;
      patch_instruction(q, translate_branch(q, p));
      check(instr_is_branch_to_addr(p, addr));
      check(instr_is_branch_to_addr(q, addr));

      /* Jump to x + 16 MB moved to x - 16 MB + 4 */
      p = buf + 0x1000000;
      addr = 0x2000000 + (unsigned long)buf;
      patch_branch(p, addr, 0);
      q = buf + 4;
      patch_instruction(q, translate_branch(q, p));
      check(instr_is_branch_to_addr(p, addr));
      check(instr_is_branch_to_addr(q, addr));


      /* Conditional branch tests */

      /* Simple case, branch to self moved a little */
      p = buf;
      addr = (unsigned long)p;
      patch_instruction(p, create_cond_branch(p, addr, 0));
      check(instr_is_branch_to_addr(p, addr));
      q = p + 1;
      patch_instruction(q, translate_branch(q, p));
      check(instr_is_branch_to_addr(q, addr));

      /* Maximum negative case, move b . to addr + 32 KB */
      p = buf;
      addr = (unsigned long)p;
      patch_instruction(p, create_cond_branch(p, addr, 0xFFFFFFFC));
      q = buf + 0x8000;
      patch_instruction(q, translate_branch(q, p));
      check(instr_is_branch_to_addr(p, addr));
      check(instr_is_branch_to_addr(q, addr));
      check(*q == 0x43ff8000);

      /* Maximum positive case, move x to x - 32 KB + 4 */
      p = buf + 0x8000;
      addr = (unsigned long)p;
      patch_instruction(p, create_cond_branch(p, addr, 0xFFFFFFFC));
      q = buf + 4;
      patch_instruction(q, translate_branch(q, p));
      check(instr_is_branch_to_addr(p, addr));
      check(instr_is_branch_to_addr(q, addr));
      check(*q == 0x43ff7ffc);

      /* Jump to x + 12 KB moved to x + 20 KB */
      p = buf;
      addr = 0x3000 + (unsigned long)buf;
      patch_instruction(p, create_cond_branch(p, addr, BRANCH_SET_LINK));
      q = buf + 0x5000;
      patch_instruction(q, translate_branch(q, p));
      check(instr_is_branch_to_addr(p, addr));
      check(instr_is_branch_to_addr(q, addr));

      /* Jump to x + 8 KB moved to x - 8 KB + 4 */
      p = buf + 0x2000;
      addr = 0x4000 + (unsigned long)buf;
      patch_instruction(p, create_cond_branch(p, addr, 0));
      q = buf + 4;
      patch_instruction(q, translate_branch(q, p));
      check(instr_is_branch_to_addr(p, addr));
      check(instr_is_branch_to_addr(q, addr));

      /* Free the buffer we were using */
      vfree(buf);
}

static int __init test_code_patching(void)
{
      printk(KERN_DEBUG "Running code patching self-tests ...\n");

      test_branch_iform();
      test_branch_bform();
      test_create_function_call();
      test_translate_branch();

      return 0;
}
late_initcall(test_code_patching);

#endif /* CONFIG_CODE_PATCHING_SELFTEST */

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