| 1 | |
| 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 | ".exitcall.exit",
|
| 34 | ".modinfo",
|
| 35 | ".no_trim_symbol",
|
| 36 | "__tracepoint_check",
|
| 37 | };
|
| 38 |
|
| 39 | static bool discarded_sec(struct section *sec)
|
| 40 | {
|
| 41 | if (!(sec->sh.sh_flags & SHF_ALLOC))
|
| 42 | return true;
|
| 43 |
|
| 44 | for (int i = 0; i < ARRAY_SIZE(discarded_secs); i++)
|
| 45 | if (strstarts(sec->name, discarded_secs[i]))
|
| 46 | return true;
|
| 47 |
|
| 48 | return false;
|
| 49 | }
|
| 50 |
|
| 51 | static bool symid_needed(struct elf *elf, struct symbol *sym)
|
| 52 | {
|
| 53 | struct symbol *s;
|
| 54 |
|
| 55 | if (!is_local_sym(sym) || is_undef_sym(sym))
|
| 56 | return false;
|
| 57 |
|
| 58 | if (!is_func_sym(sym) && !is_object_sym(sym))
|
| 59 | return false;
|
| 60 |
|
| 61 | if (is_prefix_func(sym))
|
| 62 | return false;
|
| 63 |
|
| 64 | if (discarded_sec(sym->sec))
|
| 65 | return false;
|
| 66 |
|
| 67 | for_each_sym_by_name(elf, sym->name, s) {
|
| 68 | if (s == sym || is_sec_sym(s) || is_file_sym(s) || is_undef_sym(s))
|
| 69 | continue;
|
| 70 | return true;
|
| 71 | }
|
| 72 |
|
| 73 | return false;
|
| 74 | }
|
| 75 |
|
| 76 | int klp_create_symid_sections(struct objtool_file *file)
|
| 77 | {
|
| 78 | struct elf *elf = file->elf;
|
| 79 | struct klp_symid *symids;
|
| 80 | struct section *sec;
|
| 81 | struct symbol *sym;
|
| 82 | u64 nr = 0, i = 0;
|
| 83 |
|
| 84 | if (!str_ends_with(objname, "vmlinux.o"))
|
| 85 | return 0;
|
| 86 |
|
| 87 | for_each_sym(elf, sym)
|
| 88 | if (symid_needed(elf, sym))
|
| 89 | nr++;
|
| 90 |
|
| 91 | if (!nr)
|
| 92 | return 0;
|
| 93 |
|
| 94 | sec = elf_create_section(elf, KLP_SYMID_SEC, 0, sizeof(struct klp_symid),
|
| 95 | SHT_PROGBITS, 8, 0);
|
| 96 | if (!sec)
|
| 97 | return -1;
|
| 98 |
|
| 99 | symids = elf_add_data(elf, sec, NULL, nr * sizeof(struct klp_symid));
|
| 100 | if (!symids)
|
| 101 | return -1;
|
| 102 |
|
| 103 | for_each_sym(elf, sym) {
|
| 104 | if (!symid_needed(elf, sym))
|
| 105 | continue;
|
| 106 |
|
| 107 | symids[i].id = bswap_if_needed(elf, i);
|
| 108 |
|
| 109 | if (!elf_create_reloc(elf, sec,
|
| 110 | i * sizeof(struct klp_symid) +
|
| 111 | offsetof(struct klp_symid, addr),
|
| 112 | sym, 0, R_ABS64))
|
| 113 | return -1;
|
| 114 |
|
| 115 | i++;
|
| 116 | }
|
| 117 |
|
| 118 | return 0;
|
| 119 | }
|