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From:   Ilie Halip <ilie.halip@gmail.com>
Date:   Wed, 16 Sep 2020 10:03:16 +0300
Message-ID: <CAHFW8PS0WYdfO01XwmLa+3w2W-z_FF_a5eeF8Z-YfuCMQ15ccw@mail.gmail.com>
Subject: Re: [tip:x86/seves] BUILD SUCCESS WITH WARNING e6eb15c9ba3165698488ae5c34920eea20eaa38e
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Josh Poimboeuf <jpoimboe@redhat.com>,
        Marco Elver <elver@google.com>, Borislav Petkov <bp@alien8.de>,
        Rong Chen <rong.a.chen@intel.com>,
        kernel test robot <lkp@intel.com>,
        "Li, Philip" <philip.li@intel.com>, x86-ml <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        kasan-dev <kasan-dev@googlegroups.com>
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> Should objtool be made aware of the config option and then not check
> traps after no-returns?
>
> I suspect the latter, but I'm not sure how feasible it is to
> implement.  Josh, Marco, do you have thoughts on the above?

This seems to do the trick.

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e034a8f24f46..9224e6565ba2 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2612,9 +2612,10 @@ static bool is_ubsan_insn(struct instruction *insn)
                        "__ubsan_handle_builtin_unreachable"));
 }

-static bool ignore_unreachable_insn(struct instruction *insn)
+static bool ignore_unreachable_insn(struct objtool_file *file, struct
instruction *insn)
 {
        int i;
+       struct instruction *prev_insn;

        if (insn->ignore || insn->type == INSN_NOP)
                return true;
@@ -2640,7 +2641,8 @@ static bool ignore_unreachable_insn(struct
instruction *insn)
         * the UD2, which causes GCC's undefined trap logic to emit another UD2
         * (or occasionally a JMP to UD2).
         */
-       if (list_prev_entry(insn, list)->dead_end &&
+       prev_insn = list_prev_entry(insn, list);
+       if ((prev_insn->dead_end || dead_end_function(file,
prev_insn->call_dest)) &&
            (insn->type == INSN_BUG ||
             (insn->type == INSN_JUMP_UNCONDITIONAL &&
              insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
@@ -2767,7 +2769,7 @@ static int
validate_reachable_instructions(struct objtool_file *file)
                return 0;

        for_each_insn(file, insn) {
-               if (insn->visited || ignore_unreachable_insn(insn))
+               if (insn->visited || ignore_unreachable_insn(file, insn))
                        continue;

                WARN_FUNC("unreachable instruction", insn->sec, insn->offset);