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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Fri, 29 Sep 2023 08:28:45 -0700
Message-ID: <CAKwvOd=r838B622q9v_e+ViRZNctqT65t7rmA5_A7+4FhYtD_w@mail.gmail.com>
Subject: Re: [PATCH] scripts/decode_stacktrace.sh: optionally use LLVM utilities
To:     Carlos Llamas <cmllamas@google.com>
Cc:     Nathan Chancellor <nathan@kernel.org>, Tom Rix <trix@redhat.com>,
        linux-kernel@vger.kernel.org, kernel-team@android.com,
        Will Deacon <will@kernel.org>,
        John Stultz <jstultz@google.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Sami Tolvanen <samitolvanen@google.com>
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On Thu, Sep 28, 2023 at 8:48=E2=80=AFPM Carlos Llamas <cmllamas@google.com>=
 wrote:
>
> GNU's addr2line can have problems parsing a vmlinux built with LLVM,
> particularly when LTO was used. In order to decode the traces correctly
> this patch adds the ability to switch to LLVM's utilities readelf and
> addr2line. The same approach is followed by Will in [1].
>
> Before:
>   $ scripts/decode_stacktrace.sh vmlinux < kernel.log
>   [17716.240635] Call trace:
>   [17716.240646] skb_cow_data (??:?)
>   [17716.240654] esp6_input (ld-temp.o:?)
>   [17716.240666] xfrm_input (ld-temp.o:?)
>   [17716.240674] xfrm6_rcv (??:?)
>   [...]
>
> After:
>   $ LLVM=3D1 scripts/decode_stacktrace.sh vmlinux < kernel.log
>   [17716.240635] Call trace:
>   [17716.240646] skb_cow_data (include/linux/skbuff.h:2172 net/core/skbuf=
f.c:4503)
>   [17716.240654] esp6_input (net/ipv6/esp6.c:977)
>   [17716.240666] xfrm_input (net/xfrm/xfrm_input.c:659)
>   [17716.240674] xfrm6_rcv (net/ipv6/xfrm6_input.c:172)
>   [...]
>
> Note that one could set CROSS_COMPILE=3Dllvm- instead to hack around this
> issue. However, doing so can break the decodecode routine as it will
> force the selection of other LLVM utilities down the line e.g. llvm-as.
>
> [1] https://lore.kernel.org/all/20230914131225.13415-3-will@kernel.org/
>
> Cc: Will Deacon <will@kernel.org>
> Cc: John Stultz <jstultz@google.com>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Signed-off-by: Carlos Llamas <cmllamas@google.com>

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  scripts/decode_stacktrace.sh | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/decode_stacktrace.sh b/scripts/decode_stacktrace.sh
> index 564c5632e1a2..bfe5a4082d8e 100755
> --- a/scripts/decode_stacktrace.sh
> +++ b/scripts/decode_stacktrace.sh
> @@ -16,6 +16,21 @@ elif type c++filt >/dev/null 2>&1 ; then
>         cppfilt_opts=3D-i
>  fi
>
> +UTIL_SUFFIX=3D
> +if [[ -z ${LLVM:-} ]]; then
> +       UTIL_PREFIX=3D${CROSS_COMPILE:-}
> +else
> +       UTIL_PREFIX=3Dllvm-
> +       if [[ ${LLVM} =3D=3D */ ]]; then
> +               UTIL_PREFIX=3D${LLVM}${UTIL_PREFIX}
> +       elif [[ ${LLVM} =3D=3D -* ]]; then
> +               UTIL_SUFFIX=3D${LLVM}
> +       fi
> +fi
> +
> +READELF=3D${UTIL_PREFIX}readelf${UTIL_SUFFIX}
> +ADDR2LINE=3D${UTIL_PREFIX}addr2line${UTIL_SUFFIX}
> +
>  if [[ $1 =3D=3D "-r" ]] ; then
>         vmlinux=3D""
>         basepath=3D"auto"
> @@ -75,7 +90,7 @@ find_module() {
>
>         if [[ "$modpath" !=3D "" ]] ; then
>                 for fn in $(find "$modpath" -name "${module//_/[-_]}.ko*"=
) ; do
> -                       if readelf -WS "$fn" | grep -qwF .debug_line ; th=
en
> +                       if ${READELF} -WS "$fn" | grep -qwF .debug_line ;=
 then
>                                 echo $fn
>                                 return
>                         fi
> @@ -169,7 +184,7 @@ parse_symbol() {
>         if [[ $aarray_support =3D=3D true && "${cache[$module,$address]+i=
sset}" =3D=3D "isset" ]]; then
>                 local code=3D${cache[$module,$address]}
>         else
> -               local code=3D$(${CROSS_COMPILE}addr2line -i -e "$objfile"=
 "$address" 2>/dev/null)
> +               local code=3D$(${ADDR2LINE} -i -e "$objfile" "$address" 2=
>/dev/null)
>                 if [[ $aarray_support =3D=3D true ]]; then
>                         cache[$module,$address]=3D$code
>                 fi
> --
> 2.42.0.582.g8ccd20d70d-goog
>


--=20
Thanks,
~Nick Desaulniers