linux-kernel - [PATCH v2 07/11] objtool: Include weak functions in global

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Message-Id: <ede3460d63f4a65d282c86f1175bd2662c2286ba.1681342859.git.jpoimboe@kernel.org>
Date:   Wed, 12 Apr 2023 16:49:37 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>, linux-btrfs@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        linux-scsi@...r.kernel.org, linux-hyperv@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        kernel test robot <lkp@...el.com>
Subject: [PATCH v2 07/11] objtool: Include weak functions in global_noreturns check

If a global function doesn't return, and its prototype has the
__noreturn attribute, its weak counterpart must also not return so that
it matches the prototype and meets call site expectations.

To properly follow the compiled control flow at the call sites, change
the global_noreturns check to include both global and weak functions.

On the other hand, if a weak function isn't in global_noreturns, assume
the prototype doesn't have __noreturn.  Even if the weak function
doesn't return, call sites treat it like a returnable function.

Fixes the following warning:

  kernel/sched/build_policy.o: warning: objtool: do_idle() falls through to next function play_idle_precise()

Reported-by: kernel test robot <lkp@...el.com>
Link: https://lore.kernel.org/oe-kbuild-all/202304090346.erhqxnlt-lkp@intel.com/
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 tools/objtool/check.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index ed42717463f9..94c16436d990 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -236,14 +236,14 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 	if (!func)
 		return false;
 
-	if (func->bind == STB_WEAK)
-		return false;
-
-	if (func->bind == STB_GLOBAL)
+	if (func->bind == STB_GLOBAL || func->bind == STB_WEAK)
 		for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 			if (!strcmp(func->name, global_noreturns[i]))
 				return true;
 
+	if (func->bind == STB_WEAK)
+		return false;
+
 	if (!func->len)
 		return false;
 
-- 
2.39.2