linux-kernel - Re: [PATCH v4 3/3] scripts/faddr2line: Skip over mapping symbols in output from readelf

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Date:   Tue, 26 Sep 2023 01:50:20 +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 v4 3/3] scripts/faddr2line: Skip over mapping symbols in
 output from readelf

On Thu, Sep 14, 2023 at 10:12 PM Will Deacon <will@...nel.org> wrote:
>
> Mapping symbols emitted in the readelf output can confuse the
> 'faddr2line' symbol size calculation, resulting in the erroneous
> rejection of valid offsets. This is especially prevalent when building
> an arm64 kernel with CONFIG_CFI_CLANG=y, where most functions are
> prefixed with a 32-bit data value in a '$d.n' section. For example:
>
> 447538: ffff800080014b80   548 FUNC    GLOBAL DEFAULT    2 do_one_initcall
>    104: ffff800080014c74     0 NOTYPE  LOCAL  DEFAULT    2 $x.73
>    106: ffff800080014d30     0 NOTYPE  LOCAL  DEFAULT    2 $x.75
>    111: ffff800080014da4     0 NOTYPE  LOCAL  DEFAULT    2 $d.78
>    112: ffff800080014da8     0 NOTYPE  LOCAL  DEFAULT    2 $x.79
>     36: ffff800080014de0   200 FUNC    LOCAL  DEFAULT    2 run_init_process
>
> Adding a warning to do_one_initcall() results in:
>
>   | WARNING: CPU: 0 PID: 1 at init/main.c:1236 do_one_initcall+0xf4/0x260
>
> Which 'faddr2line' refuses to accept:
>
> $ ./scripts/faddr2line vmlinux do_one_initcall+0xf4/0x260
> skipping do_one_initcall address at 0xffff800080014c74 due to size mismatch (0x260 != 0x224)
> no match for do_one_initcall+0xf4/0x260
>
> Filter out these entries from readelf using a shell reimplementation of
> is_mapping_symbol(), so that the size of a symbol is calculated as a
> delta to the next symbol present in ksymtab.
>
> Cc: Josh Poimboeuf <jpoimboe@...nel.org>
> Cc: John Stultz <jstultz@...gle.com>
> Suggested-by: Masahiro Yamada <masahiroy@...nel.org>
> Signed-off-by: Will Deacon <will@...nel.org>
> ---
>  scripts/faddr2line | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/scripts/faddr2line b/scripts/faddr2line
> index 6b8206802157..20d9b3d37843 100755
> --- a/scripts/faddr2line
> +++ b/scripts/faddr2line
> @@ -179,6 +179,11 @@ __faddr2line() {
>                         local cur_sym_elf_size=${fields[2]}
>                         local cur_sym_name=${fields[7]:-}
>
> +                       # is_mapping_symbol(cur_sym_name)
> +                       if [[ ${cur_sym_name} =~ ^((\.L)|(L0)|(\$[adtx](\.|$))) ]]; then
> +                               continue
> +                       fi
> +


Too many parentheses.


The latest include/linux/module_symbol.h looks like this.

static inline int is_mapping_symbol(const char *str)
{
        if (str[0] == '.' && str[1] == 'L')
                return true;
        if (str[0] == 'L' && str[1] == '0')
                return true;
        return str[0] == '$';
}






Does this work?

if [[ ${cur_sym_name} =~ ^(\.L|L0|\$) ]]; then
        continue
fi








>                         if [[ $cur_sym_addr = $sym_addr ]] &&
>                            [[ $cur_sym_elf_size = $sym_elf_size ]] &&
>                            [[ $cur_sym_name = $sym_name ]]; then
> --
> 2.42.0.283.g2d96d420d3-goog
>


-- 
Best Regards
Masahiro Yamada