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

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Date:   Tue, 1 Aug 2023 09:50:58 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Will Deacon <will@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        Nathan Chancellor <nathan@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        John Stultz <jstultz@...gle.com>, linux-kbuild@...r.kernel.org,
        clang-built-linux <llvm@...ts.linux.dev>
Subject: Re: [PATCH v3 1/4] scripts/faddr2line: Use LLVM addr2line and readelf
 if LLVM=1

On Sat, Jul 29, 2023 at 1:48 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> 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'

^ old GNU binutils missing support for RELR relocation format.
https://maskray.me/blog/2021-10-31-relative-relocations-and-relr

> > aarch64-linux-gnu-addr2line: DWARF error: invalid or unhandled FORM value: 0x25

^ old GNU binutils missing support for DWARFv5

I suppose if someone used a new GCC with an old binutils, they could
observe the exact same errors.

> > 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.

Ah, like LLVM_PREFIX/LLVM_SUFFIX a la
commit e9c281928c24 ("kbuild: Make $(LLVM) more flexible")

Then we could have both UTIL_PREFIX+UTIL_SUFFIX.

>
> 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



-- 
Thanks,
~Nick Desaulniers