262 строки
7.5 KiB
C
262 строки
7.5 KiB
C
/*
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* Copyright (C) 2014-2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/elf.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/sort.h>
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#include <asm/cache.h>
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#include <asm/opcodes.h>
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#define PLT_ENT_STRIDE L1_CACHE_BYTES
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#define PLT_ENT_COUNT (PLT_ENT_STRIDE / sizeof(u32))
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#define PLT_ENT_SIZE (sizeof(struct plt_entries) / PLT_ENT_COUNT)
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#ifdef CONFIG_THUMB2_KERNEL
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#define PLT_ENT_LDR __opcode_to_mem_thumb32(0xf8dff000 | \
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(PLT_ENT_STRIDE - 4))
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#else
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#define PLT_ENT_LDR __opcode_to_mem_arm(0xe59ff000 | \
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(PLT_ENT_STRIDE - 8))
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#endif
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struct plt_entries {
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u32 ldr[PLT_ENT_COUNT];
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u32 lit[PLT_ENT_COUNT];
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};
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static bool in_init(const struct module *mod, unsigned long loc)
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{
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return loc - (u32)mod->init_layout.base < mod->init_layout.size;
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}
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u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
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{
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struct mod_plt_sec *pltsec = !in_init(mod, loc) ? &mod->arch.core :
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&mod->arch.init;
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struct plt_entries *plt = (struct plt_entries *)pltsec->plt->sh_addr;
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int idx = 0;
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/*
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* Look for an existing entry pointing to 'val'. Given that the
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* relocations are sorted, this will be the last entry we allocated.
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* (if one exists).
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*/
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if (pltsec->plt_count > 0) {
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plt += (pltsec->plt_count - 1) / PLT_ENT_COUNT;
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idx = (pltsec->plt_count - 1) % PLT_ENT_COUNT;
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if (plt->lit[idx] == val)
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return (u32)&plt->ldr[idx];
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idx = (idx + 1) % PLT_ENT_COUNT;
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if (!idx)
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plt++;
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}
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pltsec->plt_count++;
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BUG_ON(pltsec->plt_count * PLT_ENT_SIZE > pltsec->plt->sh_size);
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if (!idx)
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/* Populate a new set of entries */
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*plt = (struct plt_entries){
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{ [0 ... PLT_ENT_COUNT - 1] = PLT_ENT_LDR, },
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{ val, }
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};
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else
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plt->lit[idx] = val;
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return (u32)&plt->ldr[idx];
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}
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#define cmp_3way(a,b) ((a) < (b) ? -1 : (a) > (b))
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static int cmp_rel(const void *a, const void *b)
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{
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const Elf32_Rel *x = a, *y = b;
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int i;
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/* sort by type and symbol index */
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i = cmp_3way(ELF32_R_TYPE(x->r_info), ELF32_R_TYPE(y->r_info));
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if (i == 0)
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i = cmp_3way(ELF32_R_SYM(x->r_info), ELF32_R_SYM(y->r_info));
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return i;
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}
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static bool is_zero_addend_relocation(Elf32_Addr base, const Elf32_Rel *rel)
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{
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u32 *tval = (u32 *)(base + rel->r_offset);
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/*
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* Do a bitwise compare on the raw addend rather than fully decoding
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* the offset and doing an arithmetic comparison.
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* Note that a zero-addend jump/call relocation is encoded taking the
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* PC bias into account, i.e., -8 for ARM and -4 for Thumb2.
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*/
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switch (ELF32_R_TYPE(rel->r_info)) {
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u16 upper, lower;
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case R_ARM_THM_CALL:
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case R_ARM_THM_JUMP24:
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upper = __mem_to_opcode_thumb16(((u16 *)tval)[0]);
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lower = __mem_to_opcode_thumb16(((u16 *)tval)[1]);
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return (upper & 0x7ff) == 0x7ff && (lower & 0x2fff) == 0x2ffe;
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case R_ARM_CALL:
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case R_ARM_PC24:
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case R_ARM_JUMP24:
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return (__mem_to_opcode_arm(*tval) & 0xffffff) == 0xfffffe;
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}
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BUG();
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}
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static bool duplicate_rel(Elf32_Addr base, const Elf32_Rel *rel, int num)
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{
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const Elf32_Rel *prev;
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/*
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* Entries are sorted by type and symbol index. That means that,
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* if a duplicate entry exists, it must be in the preceding
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* slot.
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*/
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if (!num)
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return false;
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prev = rel + num - 1;
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return cmp_rel(rel + num, prev) == 0 &&
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is_zero_addend_relocation(base, prev);
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}
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/* Count how many PLT entries we may need */
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static unsigned int count_plts(const Elf32_Sym *syms, Elf32_Addr base,
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const Elf32_Rel *rel, int num, Elf32_Word dstidx)
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{
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unsigned int ret = 0;
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const Elf32_Sym *s;
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int i;
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for (i = 0; i < num; i++) {
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switch (ELF32_R_TYPE(rel[i].r_info)) {
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case R_ARM_CALL:
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case R_ARM_PC24:
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case R_ARM_JUMP24:
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case R_ARM_THM_CALL:
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case R_ARM_THM_JUMP24:
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/*
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* We only have to consider branch targets that resolve
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* to symbols that are defined in a different section.
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* This is not simply a heuristic, it is a fundamental
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* limitation, since there is no guaranteed way to emit
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* PLT entries sufficiently close to the branch if the
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* section size exceeds the range of a branch
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* instruction. So ignore relocations against defined
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* symbols if they live in the same section as the
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* relocation target.
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*/
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s = syms + ELF32_R_SYM(rel[i].r_info);
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if (s->st_shndx == dstidx)
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break;
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/*
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* Jump relocations with non-zero addends against
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* undefined symbols are supported by the ELF spec, but
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* do not occur in practice (e.g., 'jump n bytes past
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* the entry point of undefined function symbol f').
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* So we need to support them, but there is no need to
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* take them into consideration when trying to optimize
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* this code. So let's only check for duplicates when
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* the addend is zero. (Note that calls into the core
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* module via init PLT entries could involve section
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* relative symbol references with non-zero addends, for
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* which we may end up emitting duplicates, but the init
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* PLT is released along with the rest of the .init
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* region as soon as module loading completes.)
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*/
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if (!is_zero_addend_relocation(base, rel + i) ||
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!duplicate_rel(base, rel, i))
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ret++;
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}
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}
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return ret;
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}
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int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
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char *secstrings, struct module *mod)
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{
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unsigned long core_plts = 0;
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unsigned long init_plts = 0;
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Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;
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Elf32_Sym *syms = NULL;
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/*
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* To store the PLTs, we expand the .text section for core module code
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* and for initialization code.
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*/
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for (s = sechdrs; s < sechdrs_end; ++s) {
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if (strcmp(".plt", secstrings + s->sh_name) == 0)
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mod->arch.core.plt = s;
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else if (strcmp(".init.plt", secstrings + s->sh_name) == 0)
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mod->arch.init.plt = s;
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else if (s->sh_type == SHT_SYMTAB)
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syms = (Elf32_Sym *)s->sh_addr;
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}
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if (!mod->arch.core.plt || !mod->arch.init.plt) {
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pr_err("%s: module PLT section(s) missing\n", mod->name);
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return -ENOEXEC;
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}
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if (!syms) {
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pr_err("%s: module symtab section missing\n", mod->name);
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return -ENOEXEC;
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}
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for (s = sechdrs + 1; s < sechdrs_end; ++s) {
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Elf32_Rel *rels = (void *)ehdr + s->sh_offset;
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int numrels = s->sh_size / sizeof(Elf32_Rel);
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Elf32_Shdr *dstsec = sechdrs + s->sh_info;
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if (s->sh_type != SHT_REL)
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continue;
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/* ignore relocations that operate on non-exec sections */
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if (!(dstsec->sh_flags & SHF_EXECINSTR))
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continue;
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/* sort by type and symbol index */
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sort(rels, numrels, sizeof(Elf32_Rel), cmp_rel, NULL);
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if (strncmp(secstrings + dstsec->sh_name, ".init", 5) != 0)
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core_plts += count_plts(syms, dstsec->sh_addr, rels,
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numrels, s->sh_info);
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else
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init_plts += count_plts(syms, dstsec->sh_addr, rels,
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numrels, s->sh_info);
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}
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mod->arch.core.plt->sh_type = SHT_NOBITS;
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mod->arch.core.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
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mod->arch.core.plt->sh_addralign = L1_CACHE_BYTES;
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mod->arch.core.plt->sh_size = round_up(core_plts * PLT_ENT_SIZE,
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sizeof(struct plt_entries));
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mod->arch.core.plt_count = 0;
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mod->arch.init.plt->sh_type = SHT_NOBITS;
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mod->arch.init.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
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mod->arch.init.plt->sh_addralign = L1_CACHE_BYTES;
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mod->arch.init.plt->sh_size = round_up(init_plts * PLT_ENT_SIZE,
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sizeof(struct plt_entries));
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mod->arch.init.plt_count = 0;
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pr_debug("%s: plt=%x, init.plt=%x\n", __func__,
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mod->arch.core.plt->sh_size, mod->arch.init.plt->sh_size);
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return 0;
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}
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