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@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lore.kernel.org/r/ede3460d63f4a65d282c86f1175bd2662c2286ba.1681342859.git.jpoimboe@kernel.org

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8d073bfd7d7fa406ab99f30901327d2d4fdf8f1e..ae0c94285124b4f95619632b1cbae291bfc64aba 100644 (file)
--- 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;