1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * Emit the .klp.symid table which allows "objtool klp diff" to reliably 4 * disambiguate duplicate-named local symbols in vmlinux. 5 * 6 * Livepatch identifies a duplicate-named symbol by its position (sympos) 7 * among the same-named kallsyms entries, counted in ascending address order 8 * in the final linked vmlinux. That order can't be derived from vmlinux.o 9 * alone: the final link reorders sub-sections (.text.unlikely*, .data..*, 10 * etc). 11 * 12 * Bridge the gap with a table which survives the final link: a single 13 * non-alloc section containing an array of { id, addr } entries, where 14 * 'id' is a unique counter identifier and 'addr' has a relocation to the 15 * symbol. The linker copies 'id' verbatim and resolves 'addr' to the symbol's 16 * final address. 17 * 18 * The table is only emitted for vmlinux.o, and only when klp-build asks for it 19 * with KLP_SYMIDS=1, which adds --klp-symids to the vmlinux.o objtool run. 20 * 21 * It can't survive --gc-sections, which sweeps the whole section; klp-build 22 * rejects CONFIG_LD_DEAD_CODE_DATA_ELIMINATION. 23 */ 24 #include <linux/string.h> 25 26 #include <objtool/objtool.h> 27 #include <objtool/warn.h> 28 #include <objtool/endianness.h> 29 #include <objtool/klp.h> 30 31 static const char * const discarded_secs[] = { 32 ".discard", 33 ".modinfo", 34 "__tracepoint_check", 35 }; 36 37 static bool discarded_sec(struct section *sec) 38 { 39 if (!(sec->sh.sh_flags & SHF_ALLOC)) 40 return true; 41 42 for (int i = 0; i < ARRAY_SIZE(discarded_secs); i++) 43 if (strstarts(sec->name, discarded_secs[i])) 44 return true; 45 46 return false; 47 } 48 49 static bool symid_needed(struct elf *elf, struct symbol *sym) 50 { 51 struct symbol *s; 52 53 if (!is_local_sym(sym) || is_undef_sym(sym)) 54 return false; 55 56 if (!is_func_sym(sym) && !is_object_sym(sym)) 57 return false; 58 59 if (is_prefix_func(sym)) 60 return false; 61 62 if (discarded_sec(sym->sec)) 63 return false; 64 65 for_each_sym_by_name(elf, sym->name, s) { 66 if (s == sym || is_sec_sym(s) || is_file_sym(s) || is_undef_sym(s)) 67 continue; 68 return true; 69 } 70 71 return false; 72 } 73 74 int klp_create_symid_sections(struct objtool_file *file) 75 { 76 struct elf *elf = file->elf; 77 struct klp_symid *symids; 78 struct section *sec; 79 struct symbol *sym; 80 u64 nr = 0, i = 0; 81 82 if (!str_ends_with(objname, "vmlinux.o")) 83 return 0; 84 85 for_each_sym(elf, sym) 86 if (symid_needed(elf, sym)) 87 nr++; 88 89 if (!nr) 90 return 0; 91 92 sec = elf_create_section(elf, KLP_SYMID_SEC, 0, sizeof(struct klp_symid), 93 SHT_PROGBITS, 8, 0); 94 if (!sec) 95 return -1; 96 97 symids = elf_add_data(elf, sec, NULL, nr * sizeof(struct klp_symid)); 98 if (!symids) 99 return -1; 100 101 for_each_sym(elf, sym) { 102 if (!symid_needed(elf, sym)) 103 continue; 104 105 symids[i].id = bswap_if_needed(elf, i); 106 107 if (!elf_create_reloc(elf, sec, 108 i * sizeof(struct klp_symid) + 109 offsetof(struct klp_symid, addr), 110 sym, 0, R_ABS64)) 111 return -1; 112 113 i++; 114 } 115 116 return 0; 117 } 118