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module_32.c

/*  Kernel module help for PPC.
    Copyright (C) 2001 Rusty Russell.

    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.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/
#include <linux/module.h>
#include <linux/moduleloader.h>
#include <linux/elf.h>
#include <linux/vmalloc.h>
#include <linux/fs.h>
#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/cache.h>
#include <linux/bug.h>
#include <linux/sort.h>

#include "setup.h"

#if 0
#define DEBUGP printk
#else
#define DEBUGP(fmt , ...)
#endif

/* Count how many different relocations (different symbol, different
   addend) */
static unsigned int count_relocs(const Elf32_Rela *rela, unsigned int num)
{
      unsigned int i, r_info, r_addend, _count_relocs;

      _count_relocs = 0;
      r_info = 0;
      r_addend = 0;
      for (i = 0; i < num; i++)
            /* Only count 24-bit relocs, others don't need stubs */
            if (ELF32_R_TYPE(rela[i].r_info) == R_PPC_REL24 &&
                (r_info != ELF32_R_SYM(rela[i].r_info) ||
                 r_addend != rela[i].r_addend)) {
                  _count_relocs++;
                  r_info = ELF32_R_SYM(rela[i].r_info);
                  r_addend = rela[i].r_addend;
            }

      return _count_relocs;
}

static int relacmp(const void *_x, const void *_y)
{
      const Elf32_Rela *x, *y;

      y = (Elf32_Rela *)_x;
      x = (Elf32_Rela *)_y;

      /* Compare the entire r_info (as opposed to ELF32_R_SYM(r_info) only) to
       * make the comparison cheaper/faster. It won't affect the sorting or
       * the counting algorithms' performance
       */
      if (x->r_info < y->r_info)
            return -1;
      else if (x->r_info > y->r_info)
            return 1;
      else if (x->r_addend < y->r_addend)
            return -1;
      else if (x->r_addend > y->r_addend)
            return 1;
      else
            return 0;
}

static void relaswap(void *_x, void *_y, int size)
{
      uint32_t *x, *y, tmp;
      int i;

      y = (uint32_t *)_x;
      x = (uint32_t *)_y;

      for (i = 0; i < sizeof(Elf32_Rela) / sizeof(uint32_t); i++) {
            tmp = x[i];
            x[i] = y[i];
            y[i] = tmp;
      }
}

/* Get the potential trampolines size required of the init and
   non-init sections */
static unsigned long get_plt_size(const Elf32_Ehdr *hdr,
                          const Elf32_Shdr *sechdrs,
                          const char *secstrings,
                          int is_init)
{
      unsigned long ret = 0;
      unsigned i;

      /* Everything marked ALLOC (this includes the exported
           symbols) */
      for (i = 1; i < hdr->e_shnum; i++) {
            /* If it's called *.init*, and we're not init, we're
                   not interested */
            if ((strstr(secstrings + sechdrs[i].sh_name, ".init") != 0)
                != is_init)
                  continue;

            /* We don't want to look at debug sections. */
            if (strstr(secstrings + sechdrs[i].sh_name, ".debug") != 0)
                  continue;

            if (sechdrs[i].sh_type == SHT_RELA) {
                  DEBUGP("Found relocations in section %u\n", i);
                  DEBUGP("Ptr: %p.  Number: %u\n",
                         (void *)hdr + sechdrs[i].sh_offset,
                         sechdrs[i].sh_size / sizeof(Elf32_Rela));

                  /* Sort the relocation information based on a symbol and
                   * addend key. This is a stable O(n*log n) complexity
                   * alogrithm but it will reduce the complexity of
                   * count_relocs() to linear complexity O(n)
                   */
                  sort((void *)hdr + sechdrs[i].sh_offset,
                       sechdrs[i].sh_size / sizeof(Elf32_Rela),
                       sizeof(Elf32_Rela), relacmp, relaswap);

                  ret += count_relocs((void *)hdr
                                   + sechdrs[i].sh_offset,
                                   sechdrs[i].sh_size
                                   / sizeof(Elf32_Rela))
                        * sizeof(struct ppc_plt_entry);
            }
      }

      return ret;
}

int module_frob_arch_sections(Elf32_Ehdr *hdr,
                        Elf32_Shdr *sechdrs,
                        char *secstrings,
                        struct module *me)
{
      unsigned int i;

      /* Find .plt and .init.plt sections */
      for (i = 0; i < hdr->e_shnum; i++) {
            if (strcmp(secstrings + sechdrs[i].sh_name, ".init.plt") == 0)
                  me->arch.init_plt_section = i;
            else if (strcmp(secstrings + sechdrs[i].sh_name, ".plt") == 0)
                  me->arch.core_plt_section = i;
      }
      if (!me->arch.core_plt_section || !me->arch.init_plt_section) {
            printk("Module doesn't contain .plt or .init.plt sections.\n");
            return -ENOEXEC;
      }

      /* Override their sizes */
      sechdrs[me->arch.core_plt_section].sh_size
            = get_plt_size(hdr, sechdrs, secstrings, 0);
      sechdrs[me->arch.init_plt_section].sh_size
            = get_plt_size(hdr, sechdrs, secstrings, 1);
      return 0;
}

int apply_relocate(Elf32_Shdr *sechdrs,
               const char *strtab,
               unsigned int symindex,
               unsigned int relsec,
               struct module *module)
{
      printk(KERN_ERR "%s: Non-ADD RELOCATION unsupported\n",
             module->name);
      return -ENOEXEC;
}

static inline int entry_matches(struct ppc_plt_entry *entry, Elf32_Addr val)
{
      if (entry->jump[0] == 0x3d600000 + ((val + 0x8000) >> 16)
          && entry->jump[1] == 0x396b0000 + (val & 0xffff))
            return 1;
      return 0;
}

/* Set up a trampoline in the PLT to bounce us to the distant function */
static uint32_t do_plt_call(void *location,
                      Elf32_Addr val,
                      Elf32_Shdr *sechdrs,
                      struct module *mod)
{
      struct ppc_plt_entry *entry;

      DEBUGP("Doing plt for call to 0x%x at 0x%x\n", val, (unsigned int)location);
      /* Init, or core PLT? */
      if (location >= mod->module_core
          && location < mod->module_core + mod->core_size)
            entry = (void *)sechdrs[mod->arch.core_plt_section].sh_addr;
      else
            entry = (void *)sechdrs[mod->arch.init_plt_section].sh_addr;

      /* Find this entry, or if that fails, the next avail. entry */
      while (entry->jump[0]) {
            if (entry_matches(entry, val)) return (uint32_t)entry;
            entry++;
      }

      /* Stolen from Paul Mackerras as well... */
      entry->jump[0] = 0x3d600000+((val+0x8000)>>16); /* lis r11,sym@ha */
      entry->jump[1] = 0x396b0000 + (val&0xffff);     /* addi r11,r11,sym@l*/
      entry->jump[2] = 0x7d6903a6;              /* mtctr r11 */
      entry->jump[3] = 0x4e800420;              /* bctr */

      DEBUGP("Initialized plt for 0x%x at %p\n", val, entry);
      return (uint32_t)entry;
}

int apply_relocate_add(Elf32_Shdr *sechdrs,
                   const char *strtab,
                   unsigned int symindex,
                   unsigned int relsec,
                   struct module *module)
{
      unsigned int i;
      Elf32_Rela *rela = (void *)sechdrs[relsec].sh_addr;
      Elf32_Sym *sym;
      uint32_t *location;
      uint32_t value;

      DEBUGP("Applying ADD relocate section %u to %u\n", relsec,
             sechdrs[relsec].sh_info);
      for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rela); i++) {
            /* This is where to make the change */
            location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
                  + rela[i].r_offset;
            /* This is the symbol it is referring to.  Note that all
               undefined symbols have been resolved.  */
            sym = (Elf32_Sym *)sechdrs[symindex].sh_addr
                  + ELF32_R_SYM(rela[i].r_info);
            /* `Everything is relative'. */
            value = sym->st_value + rela[i].r_addend;

            switch (ELF32_R_TYPE(rela[i].r_info)) {
            case R_PPC_ADDR32:
                  /* Simply set it */
                  *(uint32_t *)location = value;
                  break;

            case R_PPC_ADDR16_LO:
                  /* Low half of the symbol */
                  *(uint16_t *)location = value;
                  break;

            case R_PPC_ADDR16_HI:
                  /* Higher half of the symbol */
                  *(uint16_t *)location = (value >> 16);
                  break;

            case R_PPC_ADDR16_HA:
                  /* Sign-adjusted lower 16 bits: PPC ELF ABI says:
                     (((x >> 16) + ((x & 0x8000) ? 1 : 0))) & 0xFFFF.
                     This is the same, only sane.
                   */
                  *(uint16_t *)location = (value + 0x8000) >> 16;
                  break;

            case R_PPC_REL24:
                  if ((int)(value - (uint32_t)location) < -0x02000000
                      || (int)(value - (uint32_t)location) >= 0x02000000)
                        value = do_plt_call(location, value,
                                        sechdrs, module);

                  /* Only replace bits 2 through 26 */
                  DEBUGP("REL24 value = %08X. location = %08X\n",
                         value, (uint32_t)location);
                  DEBUGP("Location before: %08X.\n",
                         *(uint32_t *)location);
                  *(uint32_t *)location
                        = (*(uint32_t *)location & ~0x03fffffc)
                        | ((value - (uint32_t)location)
                           & 0x03fffffc);
                  DEBUGP("Location after: %08X.\n",
                         *(uint32_t *)location);
                  DEBUGP("ie. jump to %08X+%08X = %08X\n",
                         *(uint32_t *)location & 0x03fffffc,
                         (uint32_t)location,
                         (*(uint32_t *)location & 0x03fffffc)
                         + (uint32_t)location);
                  break;

            case R_PPC_REL32:
                  /* 32-bit relative jump. */
                  *(uint32_t *)location = value - (uint32_t)location;
                  break;

            default:
                  printk("%s: unknown ADD relocation: %u\n",
                         module->name,
                         ELF32_R_TYPE(rela[i].r_info));
                  return -ENOEXEC;
            }
      }
      return 0;
}

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