2 * Copyright (C) 2014 Linaro Ltd. <ard.biesheuvel@linaro.org>
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License version 2 as
6 * published by the Free Software Foundation.
10 #include <linux/kernel.h>
11 #include <linux/module.h>
12 #include <linux/sort.h>
14 #include <asm/cache.h>
15 #include <asm/opcodes.h>
17 #define PLT_ENT_STRIDE L1_CACHE_BYTES
18 #define PLT_ENT_COUNT (PLT_ENT_STRIDE / sizeof(u32))
19 #define PLT_ENT_SIZE (sizeof(struct plt_entries) / PLT_ENT_COUNT)
21 #ifdef CONFIG_THUMB2_KERNEL
22 #define PLT_ENT_LDR __opcode_to_mem_thumb32(0xf8dff000 | \
25 #define PLT_ENT_LDR __opcode_to_mem_arm(0xe59ff000 | \
30 u32 ldr[PLT_ENT_COUNT];
31 u32 lit[PLT_ENT_COUNT];
34 u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
36 struct plt_entries *plt, *plt_end;
39 plt = (void *)mod->arch.plt->sh_addr;
40 plt_end = (void *)plt + mod->arch.plt->sh_size;
42 /* Look for an existing entry pointing to 'val' */
43 for (c = mod->arch.plt_count; plt < plt_end; c -= PLT_ENT_COUNT, plt++) {
47 /* Populate a new set of entries */
48 *plt = (struct plt_entries){
49 { [0 ... PLT_ENT_COUNT - 1] = PLT_ENT_LDR, },
52 mod->arch.plt_count++;
55 for (i = 0; i < PLT_ENT_COUNT; i++) {
58 mod->arch.plt_count++;
60 if (plt->lit[i] == val)
61 return (u32)&plt->ldr[i];
67 #define cmp_3way(a,b) ((a) < (b) ? -1 : (a) > (b))
69 static int cmp_rel(const void *a, const void *b)
71 const Elf32_Rel *x = a, *y = b;
74 /* sort by type and symbol index */
75 i = cmp_3way(ELF32_R_TYPE(x->r_info), ELF32_R_TYPE(y->r_info));
77 i = cmp_3way(ELF32_R_SYM(x->r_info), ELF32_R_SYM(y->r_info));
81 static bool is_zero_addend_relocation(Elf32_Addr base, const Elf32_Rel *rel)
83 u32 *tval = (u32 *)(base + rel->r_offset);
86 * Do a bitwise compare on the raw addend rather than fully decoding
87 * the offset and doing an arithmetic comparison.
88 * Note that a zero-addend jump/call relocation is encoded taking the
89 * PC bias into account, i.e., -8 for ARM and -4 for Thumb2.
91 switch (ELF32_R_TYPE(rel->r_info)) {
95 case R_ARM_THM_JUMP24:
96 upper = __mem_to_opcode_thumb16(((u16 *)tval)[0]);
97 lower = __mem_to_opcode_thumb16(((u16 *)tval)[1]);
99 return (upper & 0x7ff) == 0x7ff && (lower & 0x2fff) == 0x2ffe;
104 return (__mem_to_opcode_arm(*tval) & 0xffffff) == 0xfffffe;
109 static bool duplicate_rel(Elf32_Addr base, const Elf32_Rel *rel, int num)
111 const Elf32_Rel *prev;
114 * Entries are sorted by type and symbol index. That means that,
115 * if a duplicate entry exists, it must be in the preceding
121 prev = rel + num - 1;
122 return cmp_rel(rel + num, prev) == 0 &&
123 is_zero_addend_relocation(base, prev);
126 /* Count how many PLT entries we may need */
127 static unsigned int count_plts(const Elf32_Sym *syms, Elf32_Addr base,
128 const Elf32_Rel *rel, int num)
130 unsigned int ret = 0;
134 for (i = 0; i < num; i++) {
135 switch (ELF32_R_TYPE(rel[i].r_info)) {
140 case R_ARM_THM_JUMP24:
142 * We only have to consider branch targets that resolve
143 * to undefined symbols. This is not simply a heuristic,
144 * it is a fundamental limitation, since the PLT itself
145 * is part of the module, and needs to be within range
146 * as well, so modules can never grow beyond that limit.
148 s = syms + ELF32_R_SYM(rel[i].r_info);
149 if (s->st_shndx != SHN_UNDEF)
153 * Jump relocations with non-zero addends against
154 * undefined symbols are supported by the ELF spec, but
155 * do not occur in practice (e.g., 'jump n bytes past
156 * the entry point of undefined function symbol f').
157 * So we need to support them, but there is no need to
158 * take them into consideration when trying to optimize
159 * this code. So let's only check for duplicates when
160 * the addend is zero.
162 if (!is_zero_addend_relocation(base, rel + i) ||
163 !duplicate_rel(base, rel, i))
170 int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
171 char *secstrings, struct module *mod)
173 unsigned long plts = 0;
174 Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;
175 Elf32_Sym *syms = NULL;
178 * To store the PLTs, we expand the .text section for core module code
179 * and for initialization code.
181 for (s = sechdrs; s < sechdrs_end; ++s) {
182 if (strcmp(".plt", secstrings + s->sh_name) == 0)
184 else if (s->sh_type == SHT_SYMTAB)
185 syms = (Elf32_Sym *)s->sh_addr;
188 if (!mod->arch.plt) {
189 pr_err("%s: module PLT section missing\n", mod->name);
193 pr_err("%s: module symtab section missing\n", mod->name);
197 for (s = sechdrs + 1; s < sechdrs_end; ++s) {
198 Elf32_Rel *rels = (void *)ehdr + s->sh_offset;
199 int numrels = s->sh_size / sizeof(Elf32_Rel);
200 Elf32_Shdr *dstsec = sechdrs + s->sh_info;
202 if (s->sh_type != SHT_REL)
205 /* ignore relocations that operate on non-exec sections */
206 if (!(dstsec->sh_flags & SHF_EXECINSTR))
209 /* sort by type and symbol index */
210 sort(rels, numrels, sizeof(Elf32_Rel), cmp_rel, NULL);
212 plts += count_plts(syms, dstsec->sh_addr, rels, numrels);
215 mod->arch.plt->sh_type = SHT_NOBITS;
216 mod->arch.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
217 mod->arch.plt->sh_addralign = L1_CACHE_BYTES;
218 mod->arch.plt->sh_size = round_up(plts * PLT_ENT_SIZE,
219 sizeof(struct plt_entries));
220 mod->arch.plt_count = 0;
222 pr_debug("%s: plt=%x\n", __func__, mod->arch.plt->sh_size);