objtool: Add workaround for GCC switch jump table bug (7e578441) · Commits · 戴 / test

tools/objtool/builtin-check.c

+41 −12

Original line number	Diff line number	Diff line
		@@ -66,6 +66,7 @@ struct objtool_file {
		struct list_head insn_list;
		DECLARE_HASHTABLE(insn_hash, 16);
		struct section rodata, whitelist;
		bool ignore_unreachables;
		};

		const char *objname;
		@@ -664,13 +665,40 @@ 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 +760,6 @@ 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;
		@@ -1056,14 +1081,15 @@ static int validate_functions(struct objtool_file *file)
		if (insn->visited)
		continue;

		if (!ignore_unreachable_insn(func, insn) &&
		!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++;
		}

		insn->visited = true;
		}
		}
		}

		@@ -1133,6 +1159,9 @@ 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;

		ret = decode_sections(&file);
		if (ret < 0)

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