objtool: Make noinstr hacks optional

Objtool has some hacks in place to workaround toolchain limitations
which otherwise would break no-instrumentation rules. Make the hacks
explicit (and optional for other arches) by turning it into a cmdline
option and kernel config option.

Signed-off-by: Josh Poimboeuf <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Reviewed-by: Miroslav Benes <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/Kconfig

···
 config HAVE_JUMP_LABEL_HACK
 	bool
 
+config HAVE_NOINSTR_HACK
+	bool
+
 config HAVE_STACK_VALIDATION
 	bool
 	help

arch/x86/Kconfig

···
 	select HAVE_MOD_ARCH_SPECIFIC
 	select HAVE_MOVE_PMD
 	select HAVE_MOVE_PUD
+	select HAVE_NOINSTR_HACK		if HAVE_OBJTOOL
 	select HAVE_NMI
 	select HAVE_OBJTOOL			if X86_64
 	select HAVE_OPTPROBES

lib/Kconfig.debug

···
 	bool "Code coverage for fuzzing"
 	depends on ARCH_HAS_KCOV
 	depends on CC_HAS_SANCOV_TRACE_PC || GCC_PLUGINS
-	depends on !ARCH_WANTS_NO_INSTR || HAVE_OBJTOOL || \
+	depends on !ARCH_WANTS_NO_INSTR || HAVE_NOINSTR_HACK || \
 		   GCC_VERSION >= 120000 || CLANG_VERSION >= 130000
 	select DEBUG_FS
 	select GCC_PLUGIN_SANCOV if !CC_HAS_SANCOV_TRACE_PC
-	select OBJTOOL if HAVE_OBJTOOL
+	select OBJTOOL if HAVE_NOINSTR_HACK
 	help
 	  KCOV exposes kernel code coverage information in a form suitable
 	  for coverage-guided fuzzing (randomized testing).

lib/Kconfig.kcsan

···
 	# We can either let objtool nop __tsan_func_{entry,exit}() and builtin
 	# atomics instrumentation in .noinstr.text, or use a compiler that can
 	# implement __no_kcsan to really remove all instrumentation.
-	depends on HAVE_OBJTOOL || CC_IS_GCC || CLANG_VERSION >= 140000
-	select OBJTOOL if HAVE_OBJTOOL
+	depends on !ARCH_WANTS_NO_INSTR || HAVE_NOINSTR_HACK || \
+		   CC_IS_GCC || CLANG_VERSION >= 140000
+	select OBJTOOL if HAVE_NOINSTR_HACK
 	help
 	  Enable support for modeling a subset of weak memory, which allows
 	  detecting a subset of data races due to missing memory barriers.

scripts/Makefile.build

···
 
 objtool_args =								\
 	$(if $(CONFIG_HAVE_JUMP_LABEL_HACK), --hacks=jump_label)	\
+	$(if $(CONFIG_HAVE_NOINSTR_HACK), --hacks=noinstr)		\
 	$(if $(CONFIG_X86_KERNEL_IBT), --lto --ibt)			\
 	$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount)		\
 	$(if $(CONFIG_UNWINDER_ORC), --orc)				\

scripts/link-vmlinux.sh

···
 			objtoolopt="${objtoolopt} --hacks=jump_label"
 		fi
 
+		if is_enabled CONFIG_HAVE_NOINSTR_HACK; then
+			objtoolopt="${objtoolopt} --hacks=noinstr"
+		fi
+
 		if is_enabled CONFIG_X86_KERNEL_IBT; then
 			objtoolopt="${objtoolopt} --ibt"
 		fi

tools/objtool/builtin-check.c

···
 		found = true;
 	}
 
+	if (!str || strstr(str, "noinstr")) {
+		opts.hack_noinstr = true;
+		found = true;
+	}
+
 	return found ? 0 : -1;
 }
 
 const struct option check_options[] = {
 	OPT_GROUP("Actions:"),
-	OPT_CALLBACK_OPTARG('h', "hacks", NULL, NULL, "jump_label", "patch toolchain bugs/limitations", parse_hacks),
+	OPT_CALLBACK_OPTARG('h', "hacks", NULL, NULL, "jump_label,noinstr", "patch toolchain bugs/limitations", parse_hacks),
 	OPT_BOOLEAN('i', "ibt", &opts.ibt, "validate and annotate IBT"),
 	OPT_BOOLEAN('m', "mcount", &opts.mcount, "annotate mcount/fentry calls for ftrace"),
 	OPT_BOOLEAN('n', "noinstr", &opts.noinstr, "validate noinstr rules"),
···
 static bool opts_valid(void)
 {
 	if (opts.hack_jump_label	||
+	    opts.hack_noinstr		||
 	    opts.ibt			||
 	    opts.mcount			||
 	    opts.noinstr		||

tools/objtool/check.c

···
 	 * attribute so they need a little help, NOP out any such calls from
 	 * noinstr text.
 	 */
-	if (insn->sec->noinstr && sym->profiling_func) {
+	if (opts.hack_noinstr && insn->sec->noinstr && sym->profiling_func) {
 		if (reloc) {
 			reloc->type = R_NONE;
 			elf_write_reloc(file->elf, reloc);

tools/objtool/include/objtool/builtin.h

···
 	/* actions: */
 	bool dump_orc;
 	bool hack_jump_label;
+	bool hack_noinstr;
 	bool ibt;
 	bool mcount;
 	bool noinstr;