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Date: Thu, 20 Jan 2022 10:44:44 +0530
From: Kaiwan N Billimoria <kaiwan.billimoria@...il.com>
To: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Chi-Thanh Hoang <chithanh.hoang@...il.com>
Subject: Re: Issue using faddr2line on kernel modules
On Thu, Jan 20, 2022 at 5:13 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> On Wed, Jan 19, 2022 at 01:21:29PM -0800, Josh Poimboeuf wrote:
> > > $ nm -n ./oops_tryv2.ko |grep -C5 do_the_work
> > > 0000000000000000 r __func__.24215
> > > 0000000000000000 r __param_bug_in_workq
> > > 0000000000000000 D __this_module
> > > 0000000000000000 r _note_7
> > > 0000000000000000 T cleanup_module
> > > 0000000000000000 t do_the_work
> > > 0000000000000000 t do_the_work.cold
> > > 0000000000000000 b gctx
> > > 0000000000000000 T init_module
> > > 0000000000000000 t try_oops_exit
> > > 0000000000000000 t try_oops_init
> > > 0000000000000008 b t1
> > > $
> > >
> > > BTW, here's the code:
> > > https://github.com/PacktPublishing/Linux-Kernel-Debugging/tree/main/ch7/oops_tryv2
> >
> > Ok, it looks like the symbols aren't sorted like the code expects. I
> > need to do a more robust fix.
>
> Ok, please try this instead. This takes a much more robust approach to
> the function size calculation, using readelf to confine the symbol
> search to the section matching the original symbol.
>
> This actually has multiple fixes and cleanups, so it'll eventually be
> split up into a patch set.
Great. Am facing a few issues though:
1. Not sure if it's me but am having issues applying your patches; it
seems to fail:
$ patch -p1 --dry-run < ./fa1.patch
checking file scripts/faddr2line
Hunk #1 FAILED at 97.
Hunk #2 FAILED at 110.
Hunk #3 FAILED at 189.
3 out of 3 hunks FAILED
$
Against which ver are you generating the patch?
(Am using 5.10.60; i noticed the last commit in mainline was f5f67cc
in Nov 2018, so vanilla 5.10.60 should be fine, no?).
2. I manually applied your patch :) This is the output I then get:
$ <...>linux-5.10.60/scripts/faddr2line ./oops_tryv2.ko do_the_work+0x16f/0x194
awk: not an option: --bignum
bad symbol size: addr: 0x0000000000000000
$
(Not sure if this helps but am running on Ubuntu 20.04; my awk is mawk
v 1.3.4.20200120-2).
Thanks,
Kaiwan.
>
> ----
>
> diff --git a/scripts/faddr2line b/scripts/faddr2line
> index 6c6439f69a72..1acb68927977 100755
> --- a/scripts/faddr2line
> +++ b/scripts/faddr2line
> @@ -97,10 +97,11 @@ __faddr2line() {
> local dir_prefix=$3
> local print_warnings=$4
>
> + local first=1
> local func=${func_addr%+*}
> local offset=${func_addr#*+}
> offset=${offset%/*}
> - local size=
> + local user_size=
> [[ $func_addr =~ "/" ]] && size=${func_addr#*/}
>
> if [[ -z $func ]] || [[ -z $offset ]] || [[ $func = $func_addr ]]; then
> @@ -110,73 +111,87 @@ __faddr2line() {
> fi
>
> # Go through each of the object's symbols which match the func name.
> - # In rare cases there might be duplicates.
> - file_end=$(${SIZE} -Ax $objfile | awk '$1 == ".text" {print $2}')
> + # In rare cases there might be duplicates, in which case we print both.
> while read symbol; do
> local fields=($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))
> - if [[ -z $sym_size ]] || [[ $sym_size -le 0 ]]; then
> - warn "bad symbol size: base: $sym_base end: $sym_end"
> + local sym_addr=0x${fields[1]}
> + local sym_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: $sym_sec"
> DONE=1
> return
> fi
> - sym_size=0x$(printf %x $sym_size)
>
> - # calculate the address
> - local addr=$(($sym_base + $offset))
> - if [[ -z $addr ]] || [[ $addr = 0 ]]; then
> - warn "bad address: $sym_base + $offset"
> + # Calculate the symbol size:
> + #
> + # We can't use the ELF size, because kallsyms also includes the
> + # padding bytes in its size calculation. For kallsyms, the
> + # size calculation is the distance between the symbol and the
> + # next symbol in a sorted list.
> + local size=$(${READELF} --symbols --wide $objfile |
> + awk -v sec=$sym_sec '$7 == sec' |
> + sort --key=2 |
> + awk --bignum -v sym_addr=${sym_addr#0x} -v sym_size=${sym_size} -v sym_name=${func} -v sec_size=${sec_size} \
> + '$2 == sym_addr && $3 == sym_size && $8 == sym_name { found = 1; next } \
> + found == 1 { size = strtonum("0x" $2) - strtonum("0x" sym_addr); if (size < sym_size) next; found = 2; print size; exit } \
> + END { if (found == 1) print strtonum(sec_size) }')
> +
> + if [[ -z $size ]]; then
> + warn "bad symbol size: addr: $sym_addr"
> DONE=1
> return
> fi
> - addr=0x$(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
> + # Calculate the specified address:
> + local addr=$(($sym_addr + $offset))
> + if [[ -z $addr ]] || [[ $addr = 0 ]]; then
> + warn "bad address: $sym_addr + $offset"
> + DONE=1
> + return
> fi
> + addr=0x$(printf %x $addr)
>
> - # 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 $size ]]; then
> [[ $print_warnings = 1 ]] &&
> - echo "skipping $func address at $addr due to size mismatch ($size != $sym_size)"
> + echo "skipping $func address at $addr due to size mismatch ($user_size != $size)"
> continue;
> fi
>
> - # make sure the provided offset is within the symbol's range
> - if [[ $offset -gt $sym_size ]]; then
> + # Make sure the provided offset is within the symbol's range:
> + if [[ $offset -gt $size ]]; then
> [[ $print_warnings = 1 ]] &&
> - echo "skipping $func address at $addr due to size mismatch ($offset > $sym_size)"
> + echo "skipping $func address at $addr due to size mismatch ($offset > $size)"
> continue
> fi
>
> - # separate multiple entries with a blank line
> - [[ $FIRST = 0 ]] && echo
> - FIRST=0
> + # In case of duplicates, 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 $file_lines ]] && return
> + # Pass full address to addr2line:
> + echo "$func+$offset/$size:"
> + local output=$(${ADDR2LINE} -fpie $objfile $addr | sed "s; $dir_prefix\(\./\)*; ;")
> + [[ -z $output ]] && continue
>
> 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
> + # If --list was specified, show each line with context:
> + echo "$output" | while read -r line
> do
> echo
> echo $line
> @@ -189,7 +204,7 @@ __faddr2line() {
>
> DONE=1
>
> - done < <(${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 $objfile | awk -v fn=$func '$4 == "FUNC" && $8 == fn')
> }
>
> [[ $# -lt 2 ]] && usage
>
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