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Date: Fri, 13 May 2022 08:52:45 +0530
From: Kaiwan N Billimoria <kaiwan.billimoria@...il.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] scripts/faddr2line: Fix overlapping text section failures
Works perfectly!
Thanks Josh, awaiting the merge into mainline ...
On Fri, May 13, 2022 at 12:35 AM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
>
> There have been some recent reports of faddr2line failures:
>
> $ scripts/faddr2line sound/soundcore.ko sound_devnode+0x5/0x35
> bad symbol size: base: 0x0000000000000000 end: 0x0000000000000000
>
> $ ./scripts/faddr2line vmlinux.o enter_from_user_mode+0x24
> bad symbol size: base: 0x0000000000005fe0 end: 0x0000000000005fe0
>
> The problem is that faddr2line is based on 'nm', which has a major
> limitation: it doesn't know how to distinguish between different text
> sections. So if an offset exists in multiple text sections in the
> object, it may fail.
>
> Rewrite faddr2line to be section-aware, by basing it on readelf.
>
> Fixes: 67326666e2d4 ("scripts: add script for translating stack dump function offsets")
> Reported-by: Kaiwan N Billimoria <kaiwan.billimoria@...il.com>
> Reported-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> ---
> scripts/faddr2line | 150 +++++++++++++++++++++++++++++----------------
> 1 file changed, 97 insertions(+), 53 deletions(-)
>
> diff --git a/scripts/faddr2line b/scripts/faddr2line
> index 6c6439f69a72..0e6268d59883 100755
> --- a/scripts/faddr2line
> +++ b/scripts/faddr2line
> @@ -44,17 +44,6 @@
> set -o errexit
> set -o nounset
>
> -READELF="${CROSS_COMPILE:-}readelf"
> -ADDR2LINE="${CROSS_COMPILE:-}addr2line"
> -SIZE="${CROSS_COMPILE:-}size"
> -NM="${CROSS_COMPILE:-}nm"
> -
> -command -v awk >/dev/null 2>&1 || die "awk isn't installed"
> -command -v ${READELF} >/dev/null 2>&1 || die "readelf isn't installed"
> -command -v ${ADDR2LINE} >/dev/null 2>&1 || die "addr2line isn't installed"
> -command -v ${SIZE} >/dev/null 2>&1 || die "size isn't installed"
> -command -v ${NM} >/dev/null 2>&1 || die "nm isn't installed"
> -
> usage() {
> echo "usage: faddr2line [--list] <object file> <func+offset> <func+offset>..." >&2
> exit 1
> @@ -69,6 +58,14 @@ die() {
> exit 1
> }
>
> +READELF="${CROSS_COMPILE:-}readelf"
> +ADDR2LINE="${CROSS_COMPILE:-}addr2line"
> +AWK="awk"
> +
> +command -v ${AWK} >/dev/null 2>&1 || die "${AWK} isn't installed"
> +command -v ${READELF} >/dev/null 2>&1 || die "${READELF} isn't installed"
> +command -v ${ADDR2LINE} >/dev/null 2>&1 || die "${ADDR2LINE} isn't installed"
> +
> # Try to figure out the source directory prefix so we can remove it from the
> # addr2line output. HACK ALERT: This assumes that start_kernel() is in
> # init/main.c! This only works for vmlinux. Otherwise it falls back to
> @@ -76,7 +73,7 @@ die() {
> find_dir_prefix() {
> local objfile=$1
>
> - local start_kernel_addr=$(${READELF} -sW $objfile | awk '$8 == "start_kernel" {printf "0x%s", $2}')
> + local start_kernel_addr=$(${READELF} --symbols --wide $objfile | ${AWK} '$8 == "start_kernel" {printf "0x%s", $2}')
> [[ -z $start_kernel_addr ]] && return
>
> local file_line=$(${ADDR2LINE} -e $objfile $start_kernel_addr)
> @@ -97,86 +94,133 @@ __faddr2line() {
> local dir_prefix=$3
> local print_warnings=$4
>
> - local func=${func_addr%+*}
> + local sym_name=${func_addr%+*}
> local offset=${func_addr#*+}
> offset=${offset%/*}
> - local size=
> - [[ $func_addr =~ "/" ]] && size=${func_addr#*/}
> + local user_size=
> + [[ $func_addr =~ "/" ]] && user_size=${func_addr#*/}
>
> - if [[ -z $func ]] || [[ -z $offset ]] || [[ $func = $func_addr ]]; then
> + if [[ -z $sym_name ]] || [[ -z $offset ]] || [[ $sym_name = $func_addr ]]; then
> warn "bad func+offset $func_addr"
> DONE=1
> return
> fi
>
> # Go through each of the object's symbols which match the func name.
> - # In rare cases there might be duplicates.
> - file_end=$(${SIZE} -Ax $objfile | awk '$1 == ".text" {print $2}')
> - while read symbol; do
> - local fields=($symbol)
> - local sym_base=0x${fields[0]}
> - local sym_type=${fields[1]}
> - local sym_end=${fields[3]}
> -
> - # calculate the size
> - local sym_size=$(($sym_end - $sym_base))
> + # In rare cases there might be duplicates, in which case we print all
> + # matches.
> + while read line; do
> + local fields=($line)
> + local sym_addr=0x${fields[1]}
> + local sym_elf_size=${fields[2]}
> + local sym_sec=${fields[6]}
> +
> + # Get the section size:
> + local sec_size=$(${READELF} --section-headers --wide $objfile |
> + sed 's/\[ /\[/' |
> + ${AWK} -v sec=$sym_sec '$1 == "[" sec "]" { print "0x" $6; exit }')
> +
> + if [[ -z $sec_size ]]; then
> + warn "bad section size: section: $sym_sec"
> + DONE=1
> + return
> + fi
> +
> + # Calculate the symbol size.
> + #
> + # Unfortunately we can't use the ELF size, because kallsyms
> + # also includes the padding bytes in its size calculation. For
> + # kallsyms, the size calculation is the distance between the
> + # symbol and the next symbol in a sorted list.
> + local sym_size
> + local cur_sym_addr
> + local found=0
> + while read line; do
> + local fields=($line)
> + cur_sym_addr=0x${fields[1]}
> + local cur_sym_elf_size=${fields[2]}
> + local cur_sym_name=${fields[7]:-}
> +
> + if [[ $cur_sym_addr = $sym_addr ]] &&
> + [[ $cur_sym_elf_size = $sym_elf_size ]] &&
> + [[ $cur_sym_name = $sym_name ]]; then
> + found=1
> + continue
> + fi
> +
> + if [[ $found = 1 ]]; then
> + sym_size=$(($cur_sym_addr - $sym_addr))
> + [[ $sym_size -lt $sym_elf_size ]] && continue;
> + found=2
> + break
> + fi
> + done < <(${READELF} --symbols --wide $objfile | ${AWK} -v sec=$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"
> + DONE=1
> + return
> + fi
> +
> + # If nothing was found after the symbol, assume it's the last
> + # symbol in the section.
> + [[ $found = 1 ]] && sym_size=$(($sec_size - $sym_addr))
> +
> if [[ -z $sym_size ]] || [[ $sym_size -le 0 ]]; then
> - warn "bad symbol size: base: $sym_base end: $sym_end"
> + warn "bad symbol size: sym_addr: $sym_addr cur_sym_addr: $cur_sym_addr"
> DONE=1
> return
> fi
> +
> sym_size=0x$(printf %x $sym_size)
>
> - # calculate the address
> - local addr=$(($sym_base + $offset))
> + # Calculate the section address from user-supplied offset:
> + local addr=$(($sym_addr + $offset))
> if [[ -z $addr ]] || [[ $addr = 0 ]]; then
> - warn "bad address: $sym_base + $offset"
> + warn "bad address: $sym_addr + $offset"
> DONE=1
> return
> fi
> addr=0x$(printf %x $addr)
>
> - # weed out non-function symbols
> - if [[ $sym_type != t ]] && [[ $sym_type != T ]]; then
> - [[ $print_warnings = 1 ]] &&
> - echo "skipping $func address at $addr due to non-function symbol of type '$sym_type'"
> - continue
> - fi
> -
> - # if the user provided a size, make sure it matches the symbol's size
> - if [[ -n $size ]] && [[ $size -ne $sym_size ]]; then
> + # If the user provided a size, make sure it matches the symbol's size:
> + if [[ -n $user_size ]] && [[ $user_size -ne $sym_size ]]; then
> [[ $print_warnings = 1 ]] &&
> - echo "skipping $func address at $addr due to size mismatch ($size != $sym_size)"
> + echo "skipping $sym_name address at $addr due to size mismatch ($user_size != $sym_size)"
> continue;
> fi
>
> - # make sure the provided offset is within the symbol's range
> + # Make sure the provided offset is within the symbol's range:
> if [[ $offset -gt $sym_size ]]; then
> [[ $print_warnings = 1 ]] &&
> - echo "skipping $func address at $addr due to size mismatch ($offset > $sym_size)"
> + echo "skipping $sym_name address at $addr due to size mismatch ($offset > $sym_size)"
> continue
> fi
>
> - # separate multiple entries with a blank line
> + # In case of duplicates or multiple addresses specified on the
> + # cmdline, separate multiple entries with a blank line:
> [[ $FIRST = 0 ]] && echo
> FIRST=0
>
> - # pass real address to addr2line
> - echo "$func+$offset/$sym_size:"
> - local file_lines=$(${ADDR2LINE} -fpie $objfile $addr | sed "s; $dir_prefix\(\./\)*; ;")
> - [[ -z $file_lines ]] && return
> + echo "$sym_name+$offset/$sym_size:"
>
> + # Pass section address to addr2line and strip absolute paths
> + # from the output:
> + local output=$(${ADDR2LINE} -fpie $objfile $addr | sed "s; $dir_prefix\(\./\)*; ;")
> + [[ -z $output ]] && continue
> +
> + # Default output (non --list):
> if [[ $LIST = 0 ]]; then
> - echo "$file_lines" | while read -r line
> + echo "$output" | while read -r line
> do
> echo $line
> done
> DONE=1;
> - return
> + continue
> fi
>
> - # show each line with context
> - echo "$file_lines" | while read -r line
> + # For --list, show each line with its corresponding source code:
> + echo "$output" | while read -r line
> do
> echo
> echo $line
> @@ -184,12 +228,12 @@ __faddr2line() {
> n1=$[$n-5]
> n2=$[$n+5]
> f=$(echo $line | sed 's/.*at \(.\+\):.*/\1/g')
> - awk 'NR>=strtonum("'$n1'") && NR<=strtonum("'$n2'") { if (NR=='$n') printf(">%d<", NR); else printf(" %d ", NR); printf("\t%s\n", $0)}' $f
> + ${AWK} 'NR>=strtonum("'$n1'") && NR<=strtonum("'$n2'") { if (NR=='$n') printf(">%d<", NR); else printf(" %d ", NR); printf("\t%s\n", $0)}' $f
> done
>
> DONE=1
>
> - done < <(${NM} -n $objfile | awk -v fn=$func -v end=$file_end '$3 == fn { found=1; line=$0; start=$1; next } found == 1 { found=0; print line, "0x"$1 } END {if (found == 1) print line, end; }')
> + done < <(${READELF} --symbols --wide $objfile | ${AWK} -v fn=$sym_name '$4 == "FUNC" && $8 == fn')
> }
>
> [[ $# -lt 2 ]] && usage
> --
> 2.34.1
>
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