From 2cc17fda94c5ee8c64c2fdc2ef981fc277e2e958 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Mon, 10 Oct 2016 15:24:01 -0500 Subject: objtool: Support '-mtune=atom' stack frame setup instruction Arnd reported that enabling CONFIG_MATOM results in a bunch of objtool false positive frame pointer warnings: arch/x86/events/intel/ds.o: warning: objtool: intel_pmu_pebs_del()+0x43: call without frame pointer save/setup security/keys/keyring.o: warning: objtool: keyring_read()+0x59: call without frame pointer save/setup kernel/signal.o: warning: objtool: __dequeue_signal()+0xd8: call without frame pointer save/setup ... objtool gets confused by the fact that the '-mtune=atom' GCC option sometimes uses 'lea (%rsp),%rbp' instead of 'mov %rsp,%rbp'. The instructions are effectively the same, but objtool doesn't know about the 'lea' variant. Fix the false warnings by adding support for 'lea (%rsp),%rbp' in the objtool decoder. Reported-by: Arnd Bergmann Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- tools/objtool/arch/x86/decode.c | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'tools') diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c index c0c0b265e88e..b63a31be1218 100644 --- a/tools/objtool/arch/x86/decode.c +++ b/tools/objtool/arch/x86/decode.c @@ -98,6 +98,15 @@ int arch_decode_instruction(struct elf *elf, struct section *sec, *type = INSN_FP_SETUP; break; + case 0x8d: + if (insn.rex_prefix.bytes && + insn.rex_prefix.bytes[0] == 0x48 && + insn.modrm.nbytes && insn.modrm.bytes[0] == 0x2c && + insn.sib.nbytes && insn.sib.bytes[0] == 0x24) + /* lea %(rsp), %rbp */ + *type = INSN_FP_SETUP; + break; + case 0x90: *type = INSN_NOP; break; -- cgit v1.2.3 From 3732710ff6f2ce2b1b7f044937a422b717d4f953 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Thu, 13 Oct 2016 16:22:52 -0500 Subject: objtool: Improve rare switch jump table pattern detection GCC 6 added a new switch statement jump table optimization which makes objtool's life harder. It looks like: mov [rodata addr],%reg1 ... some instructions ... jmpq *(%reg1,%reg2,8) The optimization is quite rare, but objtool still needs to be able to identify the pattern so that it can follow all possible control flow paths related to the switch statement. In order to detect the pattern, objtool starts from the indirect jump and scans backwards through the function until it finds the first instruction in the pattern. If it encounters an unconditional jump along the way, it stops and considers the pattern to be not found. As it turns out, unconditional jumps can happen, as long as they are small forward jumps within the range being scanned. This fixes the following warnings: drivers/infiniband/sw/rxe/rxe_comp.o: warning: objtool: rxe_completer()+0x2f4: sibling call from callable instruction with changed frame pointer drivers/infiniband/sw/rxe/rxe_resp.o: warning: objtool: rxe_responder()+0x10f: sibling call from callable instruction with changed frame pointer Reported-by: Arnd Bergmann Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/8a9ed68ae1780e8d3963e4ee13f2f257fe3a3c33.1476393584.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- tools/objtool/builtin-check.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) (limited to 'tools') diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c index 143b6cdd7f06..a00a05d287e7 100644 --- a/tools/objtool/builtin-check.c +++ b/tools/objtool/builtin-check.c @@ -713,6 +713,7 @@ static struct rela *find_switch_table(struct objtool_file *file, struct instruction *insn) { struct rela *text_rela, *rodata_rela; + struct instruction *orig_insn = insn; text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); if (text_rela && text_rela->sym == file->rodata->sym) { @@ -733,10 +734,16 @@ static struct rela *find_switch_table(struct objtool_file *file, /* case 3 */ func_for_each_insn_continue_reverse(file, func, insn) { - if (insn->type == INSN_JUMP_UNCONDITIONAL || - insn->type == INSN_JUMP_DYNAMIC) + if (insn->type == INSN_JUMP_DYNAMIC) break; + /* allow small jumps within the range */ + if (insn->type == INSN_JUMP_UNCONDITIONAL && + insn->jump_dest && + (insn->jump_dest->offset <= insn->offset || + insn->jump_dest->offset >= orig_insn->offset)) + break; + text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); if (text_rela && text_rela->sym == file->rodata->sym) -- cgit v1.2.3 From 9cfffb116887b1b7c51cd4e3fa5790dc52a0758f Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Thu, 13 Oct 2016 16:22:53 -0500 Subject: objtool: Skip all "unreachable instruction" warnings for gcov kernels Recently objtool has started reporting a few "unreachable instruction" warnings when CONFIG_GCOV is enabled for newer versions of GCC. Usually this warning means there's some new control flow that objtool doesn't understand. But in this case, objtool is correct and the instructions really are inaccessible. It's an annoying quirk of gcov, but it's harmless, so it's ok to just silence the warnings. With older versions of GCC, it was relatively easy to detect gcov-specific instructions and to skip any unreachable warnings produced by them. But GCC 6 has gotten craftier. Instead of continuing to play whack-a-mole with gcov, just use a bigger, more permanent hammer and disable unreachable warnings for the whole file when gcov is enabled. This is fine to do because a) unreachable warnings are usually of questionable value; and b) gcov isn't used for production kernels and we can relax the checks a bit there. Reported-by: kbuild test robot Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Arnd Bergmann Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/38d5c87d61d9cd46486dd2c86f46603dff0df86f.1476393584.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- tools/objtool/builtin-check.c | 57 ++++++++++++++++++++----------------------- 1 file changed, 26 insertions(+), 31 deletions(-) (limited to 'tools') diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c index a00a05d287e7..4490601a9235 100644 --- a/tools/objtool/builtin-check.c +++ b/tools/objtool/builtin-check.c @@ -97,6 +97,19 @@ static struct instruction *next_insn_same_sec(struct objtool_file *file, return next; } +static bool gcov_enabled(struct objtool_file *file) +{ + struct section *sec; + struct symbol *sym; + + list_for_each_entry(sec, &file->elf->sections, list) + list_for_each_entry(sym, &sec->symbol_list, list) + if (!strncmp(sym->name, "__gcov_.", 8)) + return true; + + return false; +} + #define for_each_insn(file, insn) \ list_for_each_entry(insn, &file->insn_list, list) @@ -1041,34 +1054,6 @@ static int validate_branch(struct objtool_file *file, return 0; } -static bool is_gcov_insn(struct instruction *insn) -{ - struct rela *rela; - struct section *sec; - struct symbol *sym; - unsigned long offset; - - rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); - if (!rela) - return false; - - if (rela->sym->type != STT_SECTION) - return false; - - sec = rela->sym->sec; - offset = rela->addend + insn->offset + insn->len - rela->offset; - - list_for_each_entry(sym, &sec->symbol_list, list) { - if (sym->type != STT_OBJECT) - continue; - - if (offset >= sym->offset && offset < sym->offset + sym->len) - return (!memcmp(sym->name, "__gcov0.", 8)); - } - - return false; -} - static bool is_kasan_insn(struct instruction *insn) { return (insn->type == INSN_CALL && @@ -1090,9 +1075,6 @@ static bool ignore_unreachable_insn(struct symbol *func, if (insn->type == INSN_NOP) return true; - if (is_gcov_insn(insn)) - return true; - /* * Check if this (or a subsequent) instruction is related to * CONFIG_UBSAN or CONFIG_KASAN. @@ -1153,6 +1135,19 @@ static int validate_functions(struct objtool_file *file) ignore_unreachable_insn(func, insn)) continue; + /* + * gcov produces a lot of unreachable + * instructions. If we get an unreachable + * warning and the file has gcov enabled, just + * ignore it, and all other such warnings for + * the file. + */ + if (!file->ignore_unreachables && + gcov_enabled(file)) { + file->ignore_unreachables = true; + continue; + } + WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset); warnings++; } -- cgit v1.2.3