linux-kernel - Re: [PATCH v3 1/4] scripts/faddr2line: Use LLVM addr2line and readelf if LLVM=1

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Date:   Sun, 30 Jul 2023 05:47:45 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Will Deacon <will@...nel.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        John Stultz <jstultz@...gle.com>, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v3 1/4] scripts/faddr2line: Use LLVM addr2line and readelf
 if LLVM=1

On Fri, Jul 28, 2023 at 8:34 PM Will Deacon <will@...nel.org> wrote:
>
> GNU utilities cannot necessarily parse objects built by LLVM, which can
> result in confusing errors when using 'faddr2line':
>
> $ CROSS_COMPILE=aarch64-linux-gnu- ./scripts/faddr2line vmlinux do_one_initcall+0xf4/0x260
> aarch64-linux-gnu-addr2line: vmlinux: unknown type [0x13] section `.relr.dyn'
> aarch64-linux-gnu-addr2line: DWARF error: invalid or unhandled FORM value: 0x25
> do_one_initcall+0xf4/0x260:
> aarch64-linux-gnu-addr2line: vmlinux: unknown type [0x13] section `.relr.dyn'
> aarch64-linux-gnu-addr2line: DWARF error: invalid or unhandled FORM value: 0x25
> $x.73 at main.c:?
>
> Although this can be worked around by setting CROSS_COMPILE to "llvm=-",
> it's cleaner to follow the same syntax as the top-level Makefile and
> accept LLVM=1 as an indication to use the llvm- tools.


Just a note.
The top Makefile accepts not only LLVM=1
but also LLVM=/usr/lib/llvm-16/bin/.
The latter is useful when you want to use
a particular version or a custom one.

Another idea might be to use a generic '${prefix}'
as this is not hooked to the Makefile,
but I do not have a strong opinion.




>
> Cc: Josh Poimboeuf <jpoimboe@...nel.org>
> Cc: John Stultz <jstultz@...gle.com>
> Signed-off-by: Will Deacon <will@...nel.org>
> ---
>  scripts/faddr2line | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/faddr2line b/scripts/faddr2line
> index 0e73aca4f908..62a3fa6f6f59 100755
> --- a/scripts/faddr2line
> +++ b/scripts/faddr2line
> @@ -58,8 +58,14 @@ die() {
>         exit 1
>  }
>
> -READELF="${CROSS_COMPILE:-}readelf"
> -ADDR2LINE="${CROSS_COMPILE:-}addr2line"
> +if [ "${LLVM:-}" == "1" ]; then
> +       UTIL_PREFIX=llvm-
> +else
> +       UTIL_PREFIX=${CROSS_COMPILE:-}
> +fi
> +
> +READELF="${UTIL_PREFIX}readelf"
> +ADDR2LINE="${UTIL_PREFIX}addr2line"
>  AWK="awk"
>  GREP="grep"
>
> --
> 2.41.0.487.g6d72f3e995-goog
>


-- 
Best Regards
Masahiro Yamada