module_32.c

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/*  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/ftrace.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;
        }

#ifdef CONFIG_DYNAMIC_FTRACE
    _count_relocs++;    /* add one for ftrace_caller */
#endif
    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;
}

static inline int entry_matches(struct ppc_plt_entry *entry, Elf32_Addr val)
{
    if (entry->jump[0] == 0x3d800000 + ((val + 0x8000) >> 16)
        && entry->jump[1] == 0x398c0000 + (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++;
    }

    entry->jump[0] = 0x3d800000+((val+0x8000)>>16); /* lis r12,sym@ha */
    entry->jump[1] = 0x398c0000 + (val&0xffff);     /* addi r12,r12,sym@l*/
    entry->jump[2] = 0x7d8903a6;                    /* mtctr r12 */
    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;
        }
    }
#ifdef CONFIG_DYNAMIC_FTRACE
    module->arch.tramp =
        do_plt_call(module->module_core,
                (unsigned long)ftrace_caller,
                sechdrs, module);
#endif
    return 0;
}