linux-kernel - Re: [PATCH] scripts/decode_stacktrace.sh: optionally use LLVM utilities

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Message-ID: <CAKwvOd=r838B622q9v_e+ViRZNctqT65t7rmA5_A7+4FhYtD_w@mail.gmail.com>
Date:   Fri, 29 Sep 2023 08:28:45 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Carlos Llamas <cmllamas@...gle.com>
Cc:     Nathan Chancellor <nathan@...nel.org>, Tom Rix <trix@...hat.com>,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Will Deacon <will@...nel.org>,
        John Stultz <jstultz@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: Re: [PATCH] scripts/decode_stacktrace.sh: optionally use LLVM utilities

On Thu, Sep 28, 2023 at 8:48 PM Carlos Llamas <cmllamas@...gle.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=1 scripts/decode_stacktrace.sh vmlinux < kernel.log
>   [17716.240635] Call trace:
>   [17716.240646] skb_cow_data (include/linux/skbuff.h:2172 net/core/skbuff.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=llvm- 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@...nel.org>
> Cc: John Stultz <jstultz@...gle.com>
> Cc: Masahiro Yamada <masahiroy@...nel.org>
> Signed-off-by: Carlos Llamas <cmllamas@...gle.com>

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.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=-i
>  fi
>
> +UTIL_SUFFIX=
> +if [[ -z ${LLVM:-} ]]; then
> +       UTIL_PREFIX=${CROSS_COMPILE:-}
> +else
> +       UTIL_PREFIX=llvm-
> +       if [[ ${LLVM} == */ ]]; then
> +               UTIL_PREFIX=${LLVM}${UTIL_PREFIX}
> +       elif [[ ${LLVM} == -* ]]; then
> +               UTIL_SUFFIX=${LLVM}
> +       fi
> +fi
> +
> +READELF=${UTIL_PREFIX}readelf${UTIL_SUFFIX}
> +ADDR2LINE=${UTIL_PREFIX}addr2line${UTIL_SUFFIX}
> +
>  if [[ $1 == "-r" ]] ; then
>         vmlinux=""
>         basepath="auto"
> @@ -75,7 +90,7 @@ find_module() {
>
>         if [[ "$modpath" != "" ]] ; then
>                 for fn in $(find "$modpath" -name "${module//_/[-_]}.ko*") ; do
> -                       if readelf -WS "$fn" | grep -qwF .debug_line ; then
> +                       if ${READELF} -WS "$fn" | grep -qwF .debug_line ; then
>                                 echo $fn
>                                 return
>                         fi
> @@ -169,7 +184,7 @@ parse_symbol() {
>         if [[ $aarray_support == true && "${cache[$module,$address]+isset}" == "isset" ]]; then
>                 local code=${cache[$module,$address]}
>         else
> -               local code=$(${CROSS_COMPILE}addr2line -i -e "$objfile" "$address" 2>/dev/null)
> +               local code=$(${ADDR2LINE} -i -e "$objfile" "$address" 2>/dev/null)
>                 if [[ $aarray_support == true ]]; then
>                         cache[$module,$address]=$code
>                 fi
> --
> 2.42.0.582.g8ccd20d70d-goog
>


-- 
Thanks,
~Nick Desaulniers