Re: Issue using faddr2line on kernel modules
From: Josh Poimboeuf
Date: Thu Jan 20 2022 - 12:18:01 EST
On Thu, Jan 20, 2022 at 10:44:44AM +0530, Kaiwan N Billimoria wrote:
> On Thu, Jan 20, 2022 at 5:13 AM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> 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
> $
Hm, did you happen to have the older patch already applied? This should
be applied instead of that one. Though it's definitely possible I
messed the patch up somehow.
When saving the patch, make sure to preserve the original whitespace.
I'm adding the new patch here as an attachment, if that helps.
> 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?).
It was against a newer kernel, but yes, applying it against 5.10.60
should also work.
>
> 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).
Sorry, I didn't realize mawk was still a thing :-)
Try this one?
----
diff --git a/scripts/faddr2line b/scripts/faddr2line
index 6c6439f69a72..01f28e52f3fc 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -97,86 +97,127 @@ __faddr2line() {
local dir_prefix=$3
local print_warnings=$4
- local func=${func_addr%+*}
+ local first=1
+ 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))
- if [[ -z $sym_size ]] || [[ $sym_size -le 0 ]]; then
- warn "bad symbol size: base: $sym_base end: $sym_end"
+ # In rare cases there might be duplicates, in which case we print all
+ # matches.
+ while read line; do
+ local fields=($line)
+ local sym_addr=0x${fields[1]}
+ local sym_size=${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 + $offset"
+ # Calculate the symbol size:
+ #
+ # We can't use the ELF size, because kallsyms also includes the
+ # padding bytes in its size calculation. For kallsyms, the
+ # size calculation is the distance between the symbol and the
+ # next symbol in a sorted list.
+ local size
+ local next_sym_addr
+ local found=0
+ while read line; do
+ local fields=($line)
+ next_sym_addr=0x${fields[1]}
+ local next_sym_size=${fields[2]}
+ local next_sym_name=${fields[7]:-}
+
+ if [[ $next_sym_addr = $sym_addr ]] &&
+ [[ $next_sym_size = $sym_size ]] &&
+ [[ $next_sym_name = $sym_name ]]; then
+ found=1
+ continue
+ fi
+
+ if [[ $found = 1 ]]; then
+ size=$(($next_sym_addr - $sym_addr))
+ [[ $size -lt $sym_size ]] && continue;
+ found=2
+ break
+ fi
+ done < <(${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_size: $sym_size"
DONE=1
return
fi
- addr=0x$(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
+ [[ $found = 1 ]] && size=$(($sec_size - $sym_addr))
+
+ if [[ -z $size ]] || [[ $size -le 0 ]]; then
+ warn "bad symbol size: sym_addr: $sym_addr next_sym_addr: $next_sym_addr"
+ DONE=1
+ return
fi
+ size=0x$(printf %x $size)
- # if the user provided a size, make sure it matches the symbol's size
- if [[ -n $size ]] && [[ $size -ne $sym_size ]]; then
+ # Calculate the specified address:
+ local addr=$(($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 $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 $sym_name 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 $sym_name 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 $file_lines ]] && return
+ # Pass full address to addr2line:
+ echo "$sym_name+$offset/$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 $line
@@ -189,7 +230,7 @@ __faddr2line() {
DONE=1
- done < <(${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 $objfile | awk -v fn=$sym_name '$4 == "FUNC" && $8 == fn')
}
[[ $# -lt 2 ]] && usage
diff --git a/scripts/faddr2line b/scripts/faddr2line
index 6c6439f69a72..01f28e52f3fc 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -97,86 +97,127 @@ __faddr2line() {
local dir_prefix=$3
local print_warnings=$4
- local func=${func_addr%+*}
+ local first=1
+ 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))
- if [[ -z $sym_size ]] || [[ $sym_size -le 0 ]]; then
- warn "bad symbol size: base: $sym_base end: $sym_end"
+ # In rare cases there might be duplicates, in which case we print all
+ # matches.
+ while read line; do
+ local fields=($line)
+ local sym_addr=0x${fields[1]}
+ local sym_size=${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 + $offset"
+ # Calculate the symbol size:
+ #
+ # We can't use the ELF size, because kallsyms also includes the
+ # padding bytes in its size calculation. For kallsyms, the
+ # size calculation is the distance between the symbol and the
+ # next symbol in a sorted list.
+ local size
+ local next_sym_addr
+ local found=0
+ while read line; do
+ local fields=($line)
+ next_sym_addr=0x${fields[1]}
+ local next_sym_size=${fields[2]}
+ local next_sym_name=${fields[7]:-}
+
+ if [[ $next_sym_addr = $sym_addr ]] &&
+ [[ $next_sym_size = $sym_size ]] &&
+ [[ $next_sym_name = $sym_name ]]; then
+ found=1
+ continue
+ fi
+
+ if [[ $found = 1 ]]; then
+ size=$(($next_sym_addr - $sym_addr))
+ [[ $size -lt $sym_size ]] && continue;
+ found=2
+ break
+ fi
+ done < <(${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_size: $sym_size"
DONE=1
return
fi
- addr=0x$(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
+ [[ $found = 1 ]] && size=$(($sec_size - $sym_addr))
+
+ if [[ -z $size ]] || [[ $size -le 0 ]]; then
+ warn "bad symbol size: sym_addr: $sym_addr next_sym_addr: $next_sym_addr"
+ DONE=1
+ return
fi
+ size=0x$(printf %x $size)
- # if the user provided a size, make sure it matches the symbol's size
- if [[ -n $size ]] && [[ $size -ne $sym_size ]]; then
+ # Calculate the specified address:
+ local addr=$(($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 $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 $sym_name 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 $sym_name 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 $file_lines ]] && return
+ # Pass full address to addr2line:
+ echo "$sym_name+$offset/$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 $line
@@ -189,7 +230,7 @@ __faddr2line() {
DONE=1
- done < <(${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 $objfile | awk -v fn=$sym_name '$4 == "FUNC" && $8 == fn')
}
[[ $# -lt 2 ]] && usage