On Sat, Sep 19, 2020 at 8:41 AM Ilie Halip <ilie.ha...@gmail.com> wrote:
>
> With CONFIG_UBSAN_TRAP enabled, the compiler may insert a trap instruction
> after a call to a noreturn function. In this case, objtool warns that the
> ud2 instruction is unreachable.
>
> This is a behavior seen with clang, from the oldest version capable of
> building the mainline x64_64 kernel (9.0), to the latest experimental
> version (12.0).
>
> objtool silences similar warnings (trap after dead end instructions), so
> so expand that check to include dead end functions.
>
> Cc: Nick Desaulniers <ndesaulni...@google.com>
> Cc: Rong Chen <rong.a.c...@intel.com>
> Cc: Marco Elver <el...@google.com>
> Cc: Philip Li <philip...@intel.com>
> Cc: Borislav Petkov <b...@alien8.de>
> Cc: kasan-...@googlegroups.com
> Cc: x...@kernel.org
> Cc: clang-built-li...@googlegroups.com
> BugLink: https://github.com/ClangBuiltLinux/linux/issues/1148
> Link:
> https://lore.kernel.org/lkml/CAKwvOdmptEpi8fiOyWUo=aizjix+z+vhjom2bulprwsmtwl...@mail.gmail.com
> Suggested-by: Nick Desaulniers <ndesaulni...@google.com>
> Reviewed-by: Nick Desaulniers <ndesaulni...@google.com>
> Tested-by: Nick Desaulniers <ndesaulni...@google.com>
> Reported-by: kbuild test robot <l...@intel.com>
> Signed-off-by: Ilie Halip <ilie.ha...@gmail.com>
> ---
Tested-by: Sedat Dilek <sedat.di...@gmail.com>
- Sedat -
>
> Changed in v2:
> - added a mention that this is a clang issue across all versions
> - added Nick's Reviewed-by, Tested-by
> - added Reported-by
>
> tools/objtool/check.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index e034a8f24f46..eddf8bf16b05 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;
> @@ -2639,8 +2640,11 @@ static bool ignore_unreachable_insn(struct instruction
> *insn)
> * __builtin_unreachable(). The BUG() macro has an unreachable()
> after
> * the UD2, which causes GCC's undefined trap logic to emit another
> UD2
> * (or occasionally a JMP to UD2).
> + * CONFIG_UBSAN_TRAP may also insert a UD2 after calling a __noreturn
> + * function.
> */
> - 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 +2771,7 @@ 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);
> --
> 2.25.1
>
> --
> You received this message because you are subscribed to the Google Groups
> "Clang Built Linux" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to clang-built-linux+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/clang-built-linux/20200919064118.1899325-1-ilie.halip%40gmail.com.
