Commit 05098119 authored by Marco Elver's avatar Marco Elver Committed by Paul E. McKenney
Browse files

objtool, kcsan: Remove memory barrier instrumentation from noinstr 



Teach objtool to turn instrumentation required for memory barrier
modeling into nops in noinstr text.

The __tsan_func_entry/exit calls are still emitted by compilers even
with the __no_sanitize_thread attribute. The memory barrier
instrumentation will be inserted explicitly (without compiler help), and
thus needs to also explicitly be removed.

Signed-off-by: default avatarMarco Elver <elver@google.com>
Acked-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 0525bd82

tools/objtool/check.c

+31 −6
Original line number Diff line number Diff line
@@ -1072,11 +1072,11 @@ static void annotate_call_site(struct objtool_file *file, 
	}



	/*

	 * Many compilers cannot disable KCOV with a function attribute

	 * so they need a little help, NOP out any KCOV calls from noinstr

	 * text.

	 * Many compilers cannot disable KCOV or sanitizer calls with a function

	 * attribute so they need a little help, NOP out any such calls from

	 * noinstr text.

	 */

	if (insn->sec->noinstr && sym->kcov) {

	if (insn->sec->noinstr && sym->profiling_func) {

		if (reloc) {

			reloc->type = R_NONE;

			elf_write_reloc(file->elf, reloc);
@@ -1991,6 +1991,31 @@ static int read_intra_function_calls(struct objtool_file *file) 
	return 0;

}



/*

 * Return true if name matches an instrumentation function, where calls to that

 * function from noinstr code can safely be removed, but compilers won't do so.

 */

static bool is_profiling_func(const char *name)

{

	/*

	 * Many compilers cannot disable KCOV with a function attribute.

	 */

	if (!strncmp(name, "__sanitizer_cov_", 16))

		return true;



	/*

	 * Some compilers currently do not remove __tsan_func_entry/exit nor

	 * __tsan_atomic_signal_fence (used for barrier instrumentation) with

	 * the __no_sanitize_thread attribute, remove them. Once the kernel's

	 * minimum Clang version is 14.0, this can be removed.

	 */

	if (!strncmp(name, "__tsan_func_", 12) ||

	    !strcmp(name, "__tsan_atomic_signal_fence"))

		return true;



	return false;

}



static int classify_symbols(struct objtool_file *file)

{

	struct section *sec;
@@ -2011,8 +2036,8 @@ static int classify_symbols(struct objtool_file *file) 
			if (!strcmp(func->name, "__fentry__"))

				func->fentry = true;



			if (!strncmp(func->name, "__sanitizer_cov_", 16))

				func->kcov = true;

			if (is_profiling_func(func->name))

				func->profiling_func = true;

		}

	}

tools/objtool/include/objtool/elf.h

+1 −1
Original line number Diff line number Diff line
@@ -58,7 +58,7 @@ struct symbol { 
	u8 static_call_tramp : 1;

	u8 retpoline_thunk   : 1;

	u8 fentry            : 1;

	u8 kcov              : 1;

	u8 profiling_func    : 1;

	struct list_head pv_target;

};