linux/arch/powerpc/kernel/module_32.c
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   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*  Kernel module help for PPC.
   3    Copyright (C) 2001 Rusty Russell.
   4
   5*/
   6
   7#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   8
   9#include <linux/module.h>
  10#include <linux/moduleloader.h>
  11#include <linux/elf.h>
  12#include <linux/vmalloc.h>
  13#include <linux/fs.h>
  14#include <linux/string.h>
  15#include <linux/kernel.h>
  16#include <linux/ftrace.h>
  17#include <linux/cache.h>
  18#include <linux/bug.h>
  19#include <linux/sort.h>
  20#include <asm/setup.h>
  21
  22/* Count how many different relocations (different symbol, different
  23   addend) */
  24static unsigned int count_relocs(const Elf32_Rela *rela, unsigned int num)
  25{
  26        unsigned int i, r_info, r_addend, _count_relocs;
  27
  28        _count_relocs = 0;
  29        r_info = 0;
  30        r_addend = 0;
  31        for (i = 0; i < num; i++)
  32                /* Only count 24-bit relocs, others don't need stubs */
  33                if (ELF32_R_TYPE(rela[i].r_info) == R_PPC_REL24 &&
  34                    (r_info != ELF32_R_SYM(rela[i].r_info) ||
  35                     r_addend != rela[i].r_addend)) {
  36                        _count_relocs++;
  37                        r_info = ELF32_R_SYM(rela[i].r_info);
  38                        r_addend = rela[i].r_addend;
  39                }
  40
  41#ifdef CONFIG_DYNAMIC_FTRACE
  42        _count_relocs++;        /* add one for ftrace_caller */
  43#endif
  44        return _count_relocs;
  45}
  46
  47static int relacmp(const void *_x, const void *_y)
  48{
  49        const Elf32_Rela *x, *y;
  50
  51        y = (Elf32_Rela *)_x;
  52        x = (Elf32_Rela *)_y;
  53
  54        /* Compare the entire r_info (as opposed to ELF32_R_SYM(r_info) only) to
  55         * make the comparison cheaper/faster. It won't affect the sorting or
  56         * the counting algorithms' performance
  57         */
  58        if (x->r_info < y->r_info)
  59                return -1;
  60        else if (x->r_info > y->r_info)
  61                return 1;
  62        else if (x->r_addend < y->r_addend)
  63                return -1;
  64        else if (x->r_addend > y->r_addend)
  65                return 1;
  66        else
  67                return 0;
  68}
  69
  70/* Get the potential trampolines size required of the init and
  71   non-init sections */
  72static unsigned long get_plt_size(const Elf32_Ehdr *hdr,
  73                                  const Elf32_Shdr *sechdrs,
  74                                  const char *secstrings,
  75                                  int is_init)
  76{
  77        unsigned long ret = 0;
  78        unsigned i;
  79
  80        /* Everything marked ALLOC (this includes the exported
  81           symbols) */
  82        for (i = 1; i < hdr->e_shnum; i++) {
  83                /* If it's called *.init*, and we're not init, we're
  84                   not interested */
  85                if ((strstr(secstrings + sechdrs[i].sh_name, ".init") != NULL)
  86                    != is_init)
  87                        continue;
  88
  89                /* We don't want to look at debug sections. */
  90                if (strstr(secstrings + sechdrs[i].sh_name, ".debug"))
  91                        continue;
  92
  93                if (sechdrs[i].sh_type == SHT_RELA) {
  94                        pr_debug("Found relocations in section %u\n", i);
  95                        pr_debug("Ptr: %p.  Number: %u\n",
  96                               (void *)hdr + sechdrs[i].sh_offset,
  97                               sechdrs[i].sh_size / sizeof(Elf32_Rela));
  98
  99                        /* Sort the relocation information based on a symbol and
 100                         * addend key. This is a stable O(n*log n) complexity
 101                         * alogrithm but it will reduce the complexity of
 102                         * count_relocs() to linear complexity O(n)
 103                         */
 104                        sort((void *)hdr + sechdrs[i].sh_offset,
 105                             sechdrs[i].sh_size / sizeof(Elf32_Rela),
 106                             sizeof(Elf32_Rela), relacmp, NULL);
 107
 108                        ret += count_relocs((void *)hdr
 109                                             + sechdrs[i].sh_offset,
 110                                             sechdrs[i].sh_size
 111                                             / sizeof(Elf32_Rela))
 112                                * sizeof(struct ppc_plt_entry);
 113                }
 114        }
 115
 116        return ret;
 117}
 118
 119int module_frob_arch_sections(Elf32_Ehdr *hdr,
 120                              Elf32_Shdr *sechdrs,
 121                              char *secstrings,
 122                              struct module *me)
 123{
 124        unsigned int i;
 125
 126        /* Find .plt and .init.plt sections */
 127        for (i = 0; i < hdr->e_shnum; i++) {
 128                if (strcmp(secstrings + sechdrs[i].sh_name, ".init.plt") == 0)
 129                        me->arch.init_plt_section = i;
 130                else if (strcmp(secstrings + sechdrs[i].sh_name, ".plt") == 0)
 131                        me->arch.core_plt_section = i;
 132        }
 133        if (!me->arch.core_plt_section || !me->arch.init_plt_section) {
 134                pr_err("Module doesn't contain .plt or .init.plt sections.\n");
 135                return -ENOEXEC;
 136        }
 137
 138        /* Override their sizes */
 139        sechdrs[me->arch.core_plt_section].sh_size
 140                = get_plt_size(hdr, sechdrs, secstrings, 0);
 141        sechdrs[me->arch.init_plt_section].sh_size
 142                = get_plt_size(hdr, sechdrs, secstrings, 1);
 143        return 0;
 144}
 145
 146static inline int entry_matches(struct ppc_plt_entry *entry, Elf32_Addr val)
 147{
 148        if (entry->jump[0] != PPC_RAW_LIS(_R12, PPC_HA(val)))
 149                return 0;
 150        if (entry->jump[1] != PPC_RAW_ADDI(_R12, _R12, PPC_LO(val)))
 151                return 0;
 152        return 1;
 153}
 154
 155/* Set up a trampoline in the PLT to bounce us to the distant function */
 156static uint32_t do_plt_call(void *location,
 157                            Elf32_Addr val,
 158                            const Elf32_Shdr *sechdrs,
 159                            struct module *mod)
 160{
 161        struct ppc_plt_entry *entry;
 162
 163        pr_debug("Doing plt for call to 0x%x at 0x%x\n", val, (unsigned int)location);
 164        /* Init, or core PLT? */
 165        if (location >= mod->core_layout.base
 166            && location < mod->core_layout.base + mod->core_layout.size)
 167                entry = (void *)sechdrs[mod->arch.core_plt_section].sh_addr;
 168        else
 169                entry = (void *)sechdrs[mod->arch.init_plt_section].sh_addr;
 170
 171        /* Find this entry, or if that fails, the next avail. entry */
 172        while (entry->jump[0]) {
 173                if (entry_matches(entry, val)) return (uint32_t)entry;
 174                entry++;
 175        }
 176
 177        entry->jump[0] = PPC_RAW_LIS(_R12, PPC_HA(val));
 178        entry->jump[1] = PPC_RAW_ADDI(_R12, _R12, PPC_LO(val));
 179        entry->jump[2] = PPC_RAW_MTCTR(_R12);
 180        entry->jump[3] = PPC_RAW_BCTR();
 181
 182        pr_debug("Initialized plt for 0x%x at %p\n", val, entry);
 183        return (uint32_t)entry;
 184}
 185
 186int apply_relocate_add(Elf32_Shdr *sechdrs,
 187                       const char *strtab,
 188                       unsigned int symindex,
 189                       unsigned int relsec,
 190                       struct module *module)
 191{
 192        unsigned int i;
 193        Elf32_Rela *rela = (void *)sechdrs[relsec].sh_addr;
 194        Elf32_Sym *sym;
 195        uint32_t *location;
 196        uint32_t value;
 197
 198        pr_debug("Applying ADD relocate section %u to %u\n", relsec,
 199               sechdrs[relsec].sh_info);
 200        for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rela); i++) {
 201                /* This is where to make the change */
 202                location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
 203                        + rela[i].r_offset;
 204                /* This is the symbol it is referring to.  Note that all
 205                   undefined symbols have been resolved.  */
 206                sym = (Elf32_Sym *)sechdrs[symindex].sh_addr
 207                        + ELF32_R_SYM(rela[i].r_info);
 208                /* `Everything is relative'. */
 209                value = sym->st_value + rela[i].r_addend;
 210
 211                switch (ELF32_R_TYPE(rela[i].r_info)) {
 212                case R_PPC_ADDR32:
 213                        /* Simply set it */
 214                        *(uint32_t *)location = value;
 215                        break;
 216
 217                case R_PPC_ADDR16_LO:
 218                        /* Low half of the symbol */
 219                        *(uint16_t *)location = value;
 220                        break;
 221
 222                case R_PPC_ADDR16_HI:
 223                        /* Higher half of the symbol */
 224                        *(uint16_t *)location = (value >> 16);
 225                        break;
 226
 227                case R_PPC_ADDR16_HA:
 228                        /* Sign-adjusted lower 16 bits: PPC ELF ABI says:
 229                           (((x >> 16) + ((x & 0x8000) ? 1 : 0))) & 0xFFFF.
 230                           This is the same, only sane.
 231                         */
 232                        *(uint16_t *)location = (value + 0x8000) >> 16;
 233                        break;
 234
 235                case R_PPC_REL24:
 236                        if ((int)(value - (uint32_t)location) < -0x02000000
 237                            || (int)(value - (uint32_t)location) >= 0x02000000)
 238                                value = do_plt_call(location, value,
 239                                                    sechdrs, module);
 240
 241                        /* Only replace bits 2 through 26 */
 242                        pr_debug("REL24 value = %08X. location = %08X\n",
 243                               value, (uint32_t)location);
 244                        pr_debug("Location before: %08X.\n",
 245                               *(uint32_t *)location);
 246                        *(uint32_t *)location
 247                                = (*(uint32_t *)location & ~0x03fffffc)
 248                                | ((value - (uint32_t)location)
 249                                   & 0x03fffffc);
 250                        pr_debug("Location after: %08X.\n",
 251                               *(uint32_t *)location);
 252                        pr_debug("ie. jump to %08X+%08X = %08X\n",
 253                               *(uint32_t *)location & 0x03fffffc,
 254                               (uint32_t)location,
 255                               (*(uint32_t *)location & 0x03fffffc)
 256                               + (uint32_t)location);
 257                        break;
 258
 259                case R_PPC_REL32:
 260                        /* 32-bit relative jump. */
 261                        *(uint32_t *)location = value - (uint32_t)location;
 262                        break;
 263
 264                default:
 265                        pr_err("%s: unknown ADD relocation: %u\n",
 266                               module->name,
 267                               ELF32_R_TYPE(rela[i].r_info));
 268                        return -ENOEXEC;
 269                }
 270        }
 271
 272        return 0;
 273}
 274
 275#ifdef CONFIG_DYNAMIC_FTRACE
 276int module_finalize_ftrace(struct module *module, const Elf_Shdr *sechdrs)
 277{
 278        module->arch.tramp = do_plt_call(module->core_layout.base,
 279                                         (unsigned long)ftrace_caller,
 280                                         sechdrs, module);
 281        if (!module->arch.tramp)
 282                return -ENOENT;
 283
 284        return 0;
 285}
 286#endif
 287
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