Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752113AbcDWLK7 (ORCPT ); Sat, 23 Apr 2016 07:10:59 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:36663 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751701AbcDWLK5 (ORCPT ); Sat, 23 Apr 2016 07:10:57 -0400 Date: Sat, 23 Apr 2016 13:10:52 +0200 From: Ingo Molnar To: Linus Torvalds Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Thomas Gleixner , Andrew Morton , Arnaldo Carvalho de Melo , Jiri Olsa , Josh Poimboeuf Subject: [GIT PULL] objtool fixes Message-ID: <20160423111052.GA12566@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9972 Lines: 293 Linus, Please pull the latest core-urgent-for-linus git tree from: git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git core-urgent-for-linus # HEAD: c2bb9e32e2315971a8535fee77335c04a739d71d objtool: Fix Makefile to properly see if libelf is supported A handful of objtool fixes: two improvements to how warnings are printed plus a false positive warning fix, and build environment fix. Thanks, Ingo ------------------> Josh Poimboeuf (2): objtool: Add workaround for GCC switch jump table bug objtool: Detect falling through to the next function Steven Rostedt (1): objtool: Fix Makefile to properly see if libelf is supported Makefile | 3 +- tools/objtool/Documentation/stack-validation.txt | 38 +++++++--- tools/objtool/builtin-check.c | 97 ++++++++++++++++++------ 3 files changed, 103 insertions(+), 35 deletions(-) diff --git a/Makefile b/Makefile index 1d0aef03eae7..70ca38ef9f4b 100644 --- a/Makefile +++ b/Makefile @@ -1008,7 +1008,8 @@ prepare0: archprepare FORCE prepare: prepare0 prepare-objtool ifdef CONFIG_STACK_VALIDATION - has_libelf := $(shell echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf - &> /dev/null && echo 1 || echo 0) + has_libelf := $(call try-run,\ + echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -,1,0) ifeq ($(has_libelf),1) objtool_target := tools/objtool FORCE else diff --git a/tools/objtool/Documentation/stack-validation.txt b/tools/objtool/Documentation/stack-validation.txt index 5a95896105bc..55a60d331f47 100644 --- a/tools/objtool/Documentation/stack-validation.txt +++ b/tools/objtool/Documentation/stack-validation.txt @@ -299,18 +299,38 @@ they mean, and suggestions for how to fix them. Errors in .c files ------------------ -If you're getting an objtool error in a compiled .c file, chances are -the file uses an asm() statement which has a "call" instruction. An -asm() statement with a call instruction must declare the use of the -stack pointer in its output operand. For example, on x86_64: +1. c_file.o: warning: objtool: funcA() falls through to next function funcB() - register void *__sp asm("rsp"); - asm volatile("call func" : "+r" (__sp)); + This means that funcA() doesn't end with a return instruction or an + unconditional jump, and that objtool has determined that the function + can fall through into the next function. There could be different + reasons for this: -Otherwise the stack frame may not get created before the call. + 1) funcA()'s last instruction is a call to a "noreturn" function like + panic(). In this case the noreturn function needs to be added to + objtool's hard-coded global_noreturns array. Feel free to bug the + objtool maintainer, or you can submit a patch. -Another possible cause for errors in C code is if the Makefile removes --fno-omit-frame-pointer or adds -fomit-frame-pointer to the gcc options. + 2) funcA() uses the unreachable() annotation in a section of code + that is actually reachable. + + 3) If funcA() calls an inline function, the object code for funcA() + might be corrupt due to a gcc bug. For more details, see: + https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646 + +2. If you're getting any other objtool error in a compiled .c file, it + may be because the file uses an asm() statement which has a "call" + instruction. An asm() statement with a call instruction must declare + the use of the stack pointer in its output operand. For example, on + x86_64: + + register void *__sp asm("rsp"); + asm volatile("call func" : "+r" (__sp)); + + Otherwise the stack frame may not get created before the call. + +3. Another possible cause for errors in C code is if the Makefile removes + -fno-omit-frame-pointer or adds -fomit-frame-pointer to the gcc options. Also see the above section for .S file errors for more information what the individual error messages mean. diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c index 7515cb2e879a..e8a1e69eb92c 100644 --- a/tools/objtool/builtin-check.c +++ b/tools/objtool/builtin-check.c @@ -54,6 +54,7 @@ struct instruction { struct symbol *call_dest; struct instruction *jump_dest; struct list_head alts; + struct symbol *func; }; struct alternative { @@ -66,6 +67,7 @@ struct objtool_file { struct list_head insn_list; DECLARE_HASHTABLE(insn_hash, 16); struct section *rodata, *whitelist; + bool ignore_unreachables, c_file; }; const char *objname; @@ -228,7 +230,7 @@ static int __dead_end_function(struct objtool_file *file, struct symbol *func, } } - if (insn->type == INSN_JUMP_DYNAMIC) + if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts)) /* sibling call */ return 0; } @@ -248,6 +250,7 @@ static int dead_end_function(struct objtool_file *file, struct symbol *func) static int decode_instructions(struct objtool_file *file) { struct section *sec; + struct symbol *func; unsigned long offset; struct instruction *insn; int ret; @@ -281,6 +284,21 @@ static int decode_instructions(struct objtool_file *file) hash_add(file->insn_hash, &insn->hash, insn->offset); list_add_tail(&insn->list, &file->insn_list); } + + list_for_each_entry(func, &sec->symbol_list, list) { + if (func->type != STT_FUNC) + continue; + + if (!find_insn(file, sec, func->offset)) { + WARN("%s(): can't find starting instruction", + func->name); + return -1; + } + + func_for_each_insn(file, func, insn) + if (!insn->func) + insn->func = func; + } } return 0; @@ -664,13 +682,40 @@ static int add_func_switch_tables(struct objtool_file *file, text_rela->addend); /* - * TODO: Document where this is needed, or get rid of it. - * * rare case: jmpq *[addr](%rip) + * + * This check is for a rare gcc quirk, currently only seen in + * three driver functions in the kernel, only with certain + * obscure non-distro configs. + * + * As part of an optimization, gcc makes a copy of an existing + * switch jump table, modifies it, and then hard-codes the jump + * (albeit with an indirect jump) to use a single entry in the + * table. The rest of the jump table and some of its jump + * targets remain as dead code. + * + * In such a case we can just crudely ignore all unreachable + * instruction warnings for the entire object file. Ideally we + * would just ignore them for the function, but that would + * require redesigning the code quite a bit. And honestly + * that's just not worth doing: unreachable instruction + * warnings are of questionable value anyway, and this is such + * a rare issue. + * + * kbuild reports: + * - https://lkml.kernel.org/r/201603231906.LWcVUpxm%25fengguang.wu@intel.com + * - https://lkml.kernel.org/r/201603271114.K9i45biy%25fengguang.wu@intel.com + * - https://lkml.kernel.org/r/201603291058.zuJ6ben1%25fengguang.wu@intel.com + * + * gcc bug: + * - https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70604 */ - if (!rodata_rela) + if (!rodata_rela) { rodata_rela = find_rela_by_dest(file->rodata, text_rela->addend + 4); + if (rodata_rela) + file->ignore_unreachables = true; + } if (!rodata_rela) continue; @@ -732,9 +777,6 @@ static int decode_sections(struct objtool_file *file) { int ret; - file->whitelist = find_section_by_name(file->elf, "__func_stack_frame_non_standard"); - file->rodata = find_section_by_name(file->elf, ".rodata"); - ret = decode_instructions(file); if (ret) return ret; @@ -799,6 +841,7 @@ static int validate_branch(struct objtool_file *file, struct alternative *alt; struct instruction *insn; struct section *sec; + struct symbol *func = NULL; unsigned char state; int ret; @@ -813,6 +856,16 @@ static int validate_branch(struct objtool_file *file, } while (1) { + if (file->c_file && insn->func) { + if (func && func != insn->func) { + WARN("%s() falls through to next function %s()", + func->name, insn->func->name); + return 1; + } + + func = insn->func; + } + if (insn->visited) { if (frame_state(insn->state) != frame_state(state)) { WARN_FUNC("frame pointer state mismatch", @@ -823,13 +876,6 @@ static int validate_branch(struct objtool_file *file, return 0; } - /* - * Catch a rare case where a noreturn function falls through to - * the next function. - */ - if (is_fentry_call(insn) && (state & STATE_FENTRY)) - return 0; - insn->visited = true; insn->state = state; @@ -1035,12 +1081,8 @@ static int validate_functions(struct objtool_file *file) continue; insn = find_insn(file, sec, func->offset); - if (!insn) { - WARN("%s(): can't find starting instruction", - func->name); - warnings++; + if (!insn) continue; - } ret = validate_branch(file, insn, 0); warnings += ret; @@ -1056,13 +1098,14 @@ static int validate_functions(struct objtool_file *file) if (insn->visited) continue; - if (!ignore_unreachable_insn(func, insn) && - !warnings) { - WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset); - warnings++; - } - insn->visited = true; + + if (file->ignore_unreachables || warnings || + ignore_unreachable_insn(func, insn)) + continue; + + WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset); + warnings++; } } } @@ -1133,6 +1176,10 @@ int cmd_check(int argc, const char **argv) INIT_LIST_HEAD(&file.insn_list); hash_init(file.insn_hash); + file.whitelist = find_section_by_name(file.elf, "__func_stack_frame_non_standard"); + file.rodata = find_section_by_name(file.elf, ".rodata"); + file.ignore_unreachables = false; + file.c_file = find_section_by_name(file.elf, ".comment"); ret = decode_sections(&file); if (ret < 0)