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Date:   Tue, 27 Sep 2022 08:19:25 -0300
From:   Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
To:     Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH] scripts/faddr2line: Fix regression in name resolution on
 ppc64le
Message-ID: <YzLcPZYTWXfrU+K4@quatroqueijos.cascardo.eti.br>
References: <20220927075211.897152-1-srikar@linux.vnet.ibm.com>
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On Tue, Sep 27, 2022 at 01:22:11PM +0530, Srikar Dronamraju wrote:
> Commit 1d1a0e7c5100 ("scripts/faddr2line: Fix overlapping text section failures")
> can cause scripts/faddr2line to fail on ppc64le machines on few
> distributions, while working on other distributions. The failure can be
> attributed to difference in readelf output on various distributions.
> 
> $ ./scripts/faddr2line vmlinux find_busiest_group+0x00
> no match for find_busiest_group+0x00
> 
> Expected output was:
> $ ./scripts/faddr2line vmlinux find_busiest_group+0x00
> find_busiest_group+0x00/0x3d0:
> find_busiest_group at kernel/sched/fair.c:9595
> 
> On ppc64le, readelf adds localentry tag before the symbol name on few
> distributions and adds the localentry tag after the symbol name on few
> other distributions. This problem has been discussed in the reference
> URL given below. This problem can be overcome by filtering out
> localentry tags in readelf output. Similar fixes are already present in
> kernel by way of commits:
> 
> 1fd6cee127e2 ("libbpf: Fix VERSIONED_SYM_COUNT number parsing")
> aa915931ac3e ("libbpf: Fix readelf output parsing for Fedora")
> 
> Fixes: 1d1a0e7c5100 ("scripts/faddr2line: Fix overlapping text section failures")
> Reference: https://lore.kernel.org/bpf/20191211160133.GB4580@calabresa/
> Cc: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

Reviewed-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

The other instances of readelf --wide on faddr2line use --section-headers and
should not required the same mangling.

Cascardo.

> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
> Cc: LKML <linux-kernel@vger.kernel.org>
> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> ---
>  scripts/faddr2line | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/scripts/faddr2line b/scripts/faddr2line
> index 5514c23f45c2..0e73aca4f908 100755
> --- a/scripts/faddr2line
> +++ b/scripts/faddr2line
> @@ -74,7 +74,8 @@ command -v ${ADDR2LINE} >/dev/null 2>&1 || die "${ADDR2LINE} isn't installed"
>  find_dir_prefix() {
>  	local objfile=$1
>  
> -	local start_kernel_addr=$(${READELF} --symbols --wide $objfile | ${AWK} '$8 == "start_kernel" {printf "0x%s", $2}')
> +	local start_kernel_addr=$(${READELF} --symbols --wide $objfile | sed 's/\[.*\]//' |
> +		${AWK} '$8 == "start_kernel" {printf "0x%s", $2}')
>  	[[ -z $start_kernel_addr ]] && return
>  
>  	local file_line=$(${ADDR2LINE} -e $objfile $start_kernel_addr)
> @@ -178,7 +179,7 @@ __faddr2line() {
>  				found=2
>  				break
>  			fi
> -		done < <(${READELF} --symbols --wide $objfile | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2)
> +		done < <(${READELF} --symbols --wide $objfile | sed 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2)
>  
>  		if [[ $found = 0 ]]; then
>  			warn "can't find symbol: sym_name: $sym_name sym_sec: $sym_sec sym_addr: $sym_addr sym_elf_size: $sym_elf_size"
> @@ -259,7 +260,7 @@ __faddr2line() {
>  
>  		DONE=1
>  
> -	done < <(${READELF} --symbols --wide $objfile | ${AWK} -v fn=$sym_name '$4 == "FUNC" && $8 == fn')
> +	done < <(${READELF} --symbols --wide $objfile | sed 's/\[.*\]//' | ${AWK} -v fn=$sym_name '$4 == "FUNC" && $8 == fn')
>  }
>  
>  [[ $# -lt 2 ]] && usage
> 
> base-commit: bf682942cd26ce9cd5e87f73ae099b383041e782
> -- 
> 2.31.1
>