Commit-ID: e7c2bc37bfae120bce3e7cc8c8abf9d110af0757 Gitweb: https://git.kernel.org/tip/e7c2bc37bfae120bce3e7cc8c8abf9d110af0757 Author: Josh Poimboeuf <jpoim...@redhat.com> AuthorDate: Wed, 17 Jul 2019 20:36:53 -0500 Committer: Thomas Gleixner <t...@linutronix.de> CommitDate: Thu, 18 Jul 2019 21:01:09 +0200
objtool: Refactor jump table code Now that C jump tables are supported, call them "jump tables" instead of "switch tables". Also rename some other variables, add comments, and simplify the code flow a bit. Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Tested-by: Nick Desaulniers <ndesaulni...@google.com> Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org> Link: https://lkml.kernel.org/r/cf951b0c0641628e0b9b81f7ceccd9bcabcb4bd8.1563413318.git.jpoim...@redhat.com --- tools/objtool/check.c | 82 +++++++++++++++++++++++++++------------------------ tools/objtool/elf.c | 2 +- tools/objtool/elf.h | 2 +- 3 files changed, 46 insertions(+), 40 deletions(-) diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 7fe31e0f8afe..4525cf677a1b 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -627,7 +627,7 @@ static int add_jump_destinations(struct objtool_file *file) * However this code can't completely replace the * read_symbols() code because this doesn't detect the * case where the parent function's only reference to a - * subfunction is through a switch table. + * subfunction is through a jump table. */ if (!strstr(insn->func->name, ".cold.") && strstr(insn->jump_dest->func->name, ".cold.")) { @@ -899,20 +899,24 @@ out: return ret; } -static int add_switch_table(struct objtool_file *file, struct instruction *insn, +static int add_jump_table(struct objtool_file *file, struct instruction *insn, struct rela *table, struct rela *next_table) { struct rela *rela = table; - struct instruction *alt_insn; + struct instruction *dest_insn; struct alternative *alt; struct symbol *pfunc = insn->func->pfunc; unsigned int prev_offset = 0; - list_for_each_entry_from(rela, &table->rela_sec->rela_list, list) { + /* + * Each @rela is a switch table relocation which points to the target + * instruction. + */ + list_for_each_entry_from(rela, &table->sec->rela_list, list) { if (rela == next_table) break; - /* Make sure the switch table entries are consecutive: */ + /* Make sure the table entries are consecutive: */ if (prev_offset && rela->offset != prev_offset + 8) break; @@ -921,12 +925,12 @@ static int add_switch_table(struct objtool_file *file, struct instruction *insn, rela->addend == pfunc->offset) break; - alt_insn = find_insn(file, rela->sym->sec, rela->addend); - if (!alt_insn) + dest_insn = find_insn(file, rela->sym->sec, rela->addend); + if (!dest_insn) break; - /* Make sure the jmp dest is in the function or subfunction: */ - if (alt_insn->func->pfunc != pfunc) + /* Make sure the destination is in the same function: */ + if (dest_insn->func->pfunc != pfunc) break; alt = malloc(sizeof(*alt)); @@ -935,7 +939,7 @@ static int add_switch_table(struct objtool_file *file, struct instruction *insn, return -1; } - alt->insn = alt_insn; + alt->insn = dest_insn; list_add_tail(&alt->list, &insn->alts); prev_offset = rela->offset; } @@ -950,7 +954,7 @@ static int add_switch_table(struct objtool_file *file, struct instruction *insn, } /* - * find_switch_table() - Given a dynamic jump, find the switch jump table in + * find_jump_table() - Given a dynamic jump, find the switch jump table in * .rodata associated with it. * * There are 3 basic patterns: @@ -992,13 +996,13 @@ static int add_switch_table(struct objtool_file *file, struct instruction *insn, * * NOTE: RETPOLINE made it harder still to decode dynamic jumps. */ -static struct rela *find_switch_table(struct objtool_file *file, +static struct rela *find_jump_table(struct objtool_file *file, struct symbol *func, struct instruction *insn) { - struct rela *text_rela, *rodata_rela; + struct rela *text_rela, *table_rela; struct instruction *orig_insn = insn; - struct section *rodata_sec; + struct section *table_sec; unsigned long table_offset; /* @@ -1031,7 +1035,7 @@ static struct rela *find_switch_table(struct objtool_file *file, continue; table_offset = text_rela->addend; - rodata_sec = text_rela->sym->sec; + table_sec = text_rela->sym->sec; if (text_rela->type == R_X86_64_PC32) table_offset += 4; @@ -1045,29 +1049,31 @@ static struct rela *find_switch_table(struct objtool_file *file, * need to be placed in the C_JUMP_TABLE_SECTION section. They * have symbols associated with them. */ - if (find_symbol_containing(rodata_sec, table_offset) && - strcmp(rodata_sec->name, C_JUMP_TABLE_SECTION)) + if (find_symbol_containing(table_sec, table_offset) && + strcmp(table_sec->name, C_JUMP_TABLE_SECTION)) continue; - rodata_rela = find_rela_by_dest(rodata_sec, table_offset); - if (rodata_rela) { - /* - * Use of RIP-relative switch jumps is quite rare, and - * indicates a rare GCC quirk/bug which can leave dead - * code behind. - */ - if (text_rela->type == R_X86_64_PC32) - file->ignore_unreachables = true; + /* Each table entry has a rela associated with it. */ + table_rela = find_rela_by_dest(table_sec, table_offset); + if (!table_rela) + continue; - return rodata_rela; - } + /* + * Use of RIP-relative switch jumps is quite rare, and + * indicates a rare GCC quirk/bug which can leave dead code + * behind. + */ + if (text_rela->type == R_X86_64_PC32) + file->ignore_unreachables = true; + + return table_rela; } return NULL; } -static int add_func_switch_tables(struct objtool_file *file, +static int add_func_jump_tables(struct objtool_file *file, struct symbol *func) { struct instruction *insn, *last = NULL, *prev_jump = NULL; @@ -1080,7 +1086,7 @@ static int add_func_switch_tables(struct objtool_file *file, /* * Store back-pointers for unconditional forward jumps such - * that find_switch_table() can back-track using those and + * that find_jump_table() can back-track using those and * avoid some potentially confusing code. */ if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest && @@ -1095,17 +1101,17 @@ static int add_func_switch_tables(struct objtool_file *file, if (insn->type != INSN_JUMP_DYNAMIC) continue; - rela = find_switch_table(file, func, insn); + rela = find_jump_table(file, func, insn); if (!rela) continue; /* - * We found a switch table, but we don't know yet how big it + * We found a jump table, but we don't know yet how big it * is. Don't add it until we reach the end of the function or - * the beginning of another switch table in the same function. + * the beginning of another jump table in the same function. */ if (prev_jump) { - ret = add_switch_table(file, prev_jump, prev_rela, rela); + ret = add_jump_table(file, prev_jump, prev_rela, rela); if (ret) return ret; } @@ -1115,7 +1121,7 @@ static int add_func_switch_tables(struct objtool_file *file, } if (prev_jump) { - ret = add_switch_table(file, prev_jump, prev_rela, NULL); + ret = add_jump_table(file, prev_jump, prev_rela, NULL); if (ret) return ret; } @@ -1128,7 +1134,7 @@ static int add_func_switch_tables(struct objtool_file *file, * section which contains a list of addresses within the function to jump to. * This finds these jump tables and adds them to the insn->alts lists. */ -static int add_switch_table_alts(struct objtool_file *file) +static int add_jump_table_alts(struct objtool_file *file) { struct section *sec; struct symbol *func; @@ -1142,7 +1148,7 @@ static int add_switch_table_alts(struct objtool_file *file) if (func->type != STT_FUNC) continue; - ret = add_func_switch_tables(file, func); + ret = add_func_jump_tables(file, func); if (ret) return ret; } @@ -1339,7 +1345,7 @@ static int decode_sections(struct objtool_file *file) if (ret) return ret; - ret = add_switch_table_alts(file); + ret = add_jump_table_alts(file); if (ret) return ret; diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index 9194732a673d..edba4745f25a 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -385,7 +385,7 @@ static int read_relas(struct elf *elf) rela->offset = rela->rela.r_offset; symndx = GELF_R_SYM(rela->rela.r_info); rela->sym = find_symbol_by_index(elf, symndx); - rela->rela_sec = sec; + rela->sec = sec; if (!rela->sym) { WARN("can't find rela entry symbol %d for %s", symndx, sec->name); diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h index 2fe0b0aa741d..d4d3e0528d4a 100644 --- a/tools/objtool/elf.h +++ b/tools/objtool/elf.h @@ -57,7 +57,7 @@ struct rela { struct list_head list; struct hlist_node hash; GElf_Rela rela; - struct section *rela_sec; + struct section *sec; struct symbol *sym; unsigned int type; unsigned long offset;
