[PATCH 0/7] Improve performance of 'faddr2line'

[PATCH 0/7] Improve performance of 'faddr2line'

[Brian Johannesmeyer]

Hello,

I was looking at the performance of faddr2line and noticed that it spends
most of its time performing two tasks:
- (1) Making redundant calls to readelf and addr2line for each address
  (e.g., it makes 7 readelf calls and 2 addr2line calls when converting 1
address, and it makes 252 readelf calls and 51 addr2line calls when
converting 50 addresses); and
- (2) Calculating a symbol’s size by unnecessarily looping through every
  symbol in a particular section.

This patch series consists of the following parts:
- Patches 1-2 reduce the total number of readelf calls to one,
- Patches 3-4 make minor changes in preparation for the following patches,
- Patches 5-6 reduce the total number of addr2line calls to one, and
- Patch 7 modifies the symbol size calculation to only check two symbols.

I evaluated the performance of the patch series by running faddr2line with
a standard kernel image (X86_64 defconfig with CONFIG_DEBUG_INFO enabled).
When converting only 1 address, the patch series gives a negligible
speedup. When converting 50 addresses, however, it gives a 15x speedup.

Cheers,

Brian

Brian Johannesmeyer (7):
  scripts/faddr2line: Reduce number of readelf calls to three
  scripts/faddr2line: Combine three readelf calls into one
  scripts/faddr2line: Check vmlinux only once
  scripts/faddr2line: Pass --addresses argument to addr2line
  scripts/faddr2line: Invoke addr2line as a single long-running process
  scripts/faddr2line: Remove call to addr2line from find_dir_prefix()
  scripts/faddr2line: Check only two symbols when calculating symbol
    size

 scripts/faddr2line | 110 ++++++++++++++++++++++++++++++++++-----------
 1 file changed, 84 insertions(+), 26 deletions(-)

-- 
2.34.1

[PATCH 1/7] scripts/faddr2line: Reduce number of readelf calls to three

[Brian Johannesmeyer]

Rather than calling readelf several times for each invocation of
__faddr2line, call readelf only three times at the beginning, and save its
result for future use.

Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
---
 scripts/faddr2line | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/scripts/faddr2line b/scripts/faddr2line
index 587415a52b6f..bf394bfd526a 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -87,7 +87,7 @@ 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 | sed 's/\[.*\]//' |
+	local start_kernel_addr=$(echo "${ELF_SYMS}" | sed 's/\[.*\]//' |
 		${AWK} '$8 == "start_kernel" {printf "0x%s", $2}')
 	[[ -z $start_kernel_addr ]] && return
 
@@ -103,6 +103,14 @@ find_dir_prefix() {
 	return 0
 }
 
+run_readelf() {
+	local objfile=$1
+
+	ELF_FILEHEADER=$(${READELF} --file-header $objfile)
+	ELF_SECHEADERS=$(${READELF} --section-headers --wide $objfile)
+	ELF_SYMS=$(${READELF} --symbols --wide $objfile)
+}
+
 __faddr2line() {
 	local objfile=$1
 	local func_addr=$2
@@ -125,7 +133,7 @@ __faddr2line() {
 
 	# vmlinux uses absolute addresses in the section table rather than
 	# section offsets.
-	local file_type=$(${READELF} --file-header $objfile |
+	local file_type=$(echo "${ELF_FILEHEADER}" |
 		${AWK} '$1 == "Type:" { print $2; exit }')
 	if [[ $file_type = "EXEC" ]] || [[ $file_type == "DYN" ]]; then
 		is_vmlinux=1
@@ -143,8 +151,7 @@ __faddr2line() {
 		local sec_name
 
 		# Get the section size:
-		sec_size=$(${READELF} --section-headers --wide $objfile |
-			sed 's/\[ /\[/' |
+		sec_size=$(echo "${ELF_SECHEADERS}" | sed 's/\[ /\[/' |
 			${AWK} -v sec=$sym_sec '$1 == "[" sec "]" { print "0x" $6; exit }')
 
 		if [[ -z $sec_size ]]; then
@@ -154,8 +161,7 @@ __faddr2line() {
 		fi
 
 		# Get the section name:
-		sec_name=$(${READELF} --section-headers --wide $objfile |
-			sed 's/\[ /\[/' |
+		sec_name=$(echo "${ELF_SECHEADERS}" | sed 's/\[ /\[/' |
 			${AWK} -v sec=$sym_sec '$1 == "[" sec "]" { print $2; exit }')
 
 		if [[ -z $sec_name ]]; then
@@ -197,7 +203,7 @@ __faddr2line() {
 				found=2
 				break
 			fi
-		done < <(${READELF} --symbols --wide $objfile | sed 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2)
+		done < <(echo "${ELF_SYMS}" | 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"
@@ -278,7 +284,7 @@ __faddr2line() {
 
 		DONE=1
 
-	done < <(${READELF} --symbols --wide $objfile | sed 's/\[.*\]//' | ${AWK} -v fn=$sym_name '$8 == fn')
+	done < <(echo "${ELF_SYMS}" | sed 's/\[.*\]//' | ${AWK} -v fn=$sym_name '$8 == fn')
 }
 
 [[ $# -lt 2 ]] && usage
@@ -291,7 +297,9 @@ LIST=0
 [[ ! -f $objfile ]] && die "can't find objfile $objfile"
 shift
 
-${READELF} --section-headers --wide $objfile | ${GREP} -q '\.debug_info' || die "CONFIG_DEBUG_INFO not enabled"
+run_readelf $objfile
+
+echo "${ELF_SECHEADERS}" | ${GREP} -q '\.debug_info' || die "CONFIG_DEBUG_INFO not enabled"
 
 DIR_PREFIX=supercalifragilisticexpialidocious
 find_dir_prefix $objfile
-- 
2.34.1

[PATCH 2/7] scripts/faddr2line: Combine three readelf calls into one

[Brian Johannesmeyer]

Rather than calling readelf three separate times to collect three different
types of info, call it only once, and parse out the different types of info
from its output.

Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
---
 scripts/faddr2line | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/scripts/faddr2line b/scripts/faddr2line
index bf394bfd526a..f011bda4ed25 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -105,10 +105,14 @@ find_dir_prefix() {
 
 run_readelf() {
 	local objfile=$1
-
-	ELF_FILEHEADER=$(${READELF} --file-header $objfile)
-	ELF_SECHEADERS=$(${READELF} --section-headers --wide $objfile)
-	ELF_SYMS=$(${READELF} --symbols --wide $objfile)
+	local out=$(${READELF} --file-header --section-headers --symbols --wide $objfile)
+
+	# This assumes that readelf first prints the file header, then the section headers, then the symbols.
+	# Note: It seems that GNU readelf does not prefix section headers with the "There are X section headers"
+	# line when multiple options are given, so let's also match with the "Section Headers:" line.
+	ELF_FILEHEADER=$(echo "${out}" | sed -n '/There are [0-9]* section headers, starting at offset\|Section Headers:/q;p')
+	ELF_SECHEADERS=$(echo "${out}" | sed -n '/There are [0-9]* section headers, starting at offset\|Section Headers:/,$p' | sed -n '/Symbol table .* contains [0-9]* entries:/q;p')
+	ELF_SYMS=$(echo "${out}" | sed -n '/Symbol table .* contains [0-9]* entries:/,$p')
 }
 
 __faddr2line() {
-- 
2.34.1

[PATCH 3/7] scripts/faddr2line: Check vmlinux only once

[Brian Johannesmeyer]

Rather than checking whether the object file is vmlinux for each invocation
of __faddr2line, check it only once beforehand.

Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
---
 scripts/faddr2line | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/scripts/faddr2line b/scripts/faddr2line
index f011bda4ed25..bb3b5f03f4ea 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -115,6 +115,17 @@ run_readelf() {
 	ELF_SYMS=$(echo "${out}" | sed -n '/Symbol table .* contains [0-9]* entries:/,$p')
 }
 
+check_vmlinux() {
+	# vmlinux uses absolute addresses in the section table rather than
+	# section offsets.
+	IS_VMLINUX=0
+	local file_type=$(echo "${ELF_FILEHEADER}" |
+		${AWK} '$1 == "Type:" { print $2; exit }')
+	if [[ $file_type = "EXEC" ]] || [[ $file_type == "DYN" ]]; then
+		IS_VMLINUX=1
+	fi
+}
+
 __faddr2line() {
 	local objfile=$1
 	local func_addr=$2
@@ -125,8 +136,6 @@ __faddr2line() {
 	local func_offset=${func_addr#*+}
 	func_offset=${func_offset%/*}
 	local user_size=
-	local file_type
-	local is_vmlinux=0
 	[[ $func_addr =~ "/" ]] && user_size=${func_addr#*/}
 
 	if [[ -z $sym_name ]] || [[ -z $func_offset ]] || [[ $sym_name = $func_addr ]]; then
@@ -135,14 +144,6 @@ __faddr2line() {
 		return
 	fi
 
-	# vmlinux uses absolute addresses in the section table rather than
-	# section offsets.
-	local file_type=$(echo "${ELF_FILEHEADER}" |
-		${AWK} '$1 == "Type:" { print $2; exit }')
-	if [[ $file_type = "EXEC" ]] || [[ $file_type == "DYN" ]]; then
-		is_vmlinux=1
-	fi
-
 	# Go through each of the object's symbols which match the func name.
 	# In rare cases there might be duplicates, in which case we print all
 	# matches.
@@ -260,7 +261,7 @@ __faddr2line() {
 		# Pass section address to addr2line and strip absolute paths
 		# from the output:
 		local args="--functions --pretty-print --inlines --exe=$objfile"
-		[[ $is_vmlinux = 0 ]] && args="$args --section=$sec_name"
+		[[ $IS_VMLINUX = 0 ]] && args="$args --section=$sec_name"
 		local output=$(${ADDR2LINE} $args $addr | sed "s; $dir_prefix\(\./\)*; ;")
 		[[ -z $output ]] && continue
 
@@ -305,6 +306,8 @@ run_readelf $objfile
 
 echo "${ELF_SECHEADERS}" | ${GREP} -q '\.debug_info' || die "CONFIG_DEBUG_INFO not enabled"
 
+check_vmlinux
+
 DIR_PREFIX=supercalifragilisticexpialidocious
 find_dir_prefix $objfile
 
-- 
2.34.1

[PATCH 4/7] scripts/faddr2line: Pass --addresses argument to addr2line

[Brian Johannesmeyer]

In preparation for identifying an addr2line sentinel. See previous work
[0], which applies a similar change to perf.

[0] commit 8dc26b6f718a ("perf srcline: Make sentinel reading for binutils
addr2line more robust")

Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
---
 scripts/faddr2line | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/scripts/faddr2line b/scripts/faddr2line
index bb3b5f03f4ea..820680c59a39 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -260,9 +260,12 @@ __faddr2line() {
 
 		# Pass section address to addr2line and strip absolute paths
 		# from the output:
-		local args="--functions --pretty-print --inlines --exe=$objfile"
+		local args="--functions --pretty-print --inlines --addresses --exe=$objfile"
 		[[ $IS_VMLINUX = 0 ]] && args="$args --section=$sec_name"
-		local output=$(${ADDR2LINE} $args $addr | sed "s; $dir_prefix\(\./\)*; ;")
+		local output_with_addr=$(${ADDR2LINE} $args $addr | sed "s; $dir_prefix\(\./\)*; ;")
+		[[ -z $output_with_addr ]] && continue
+
+		local output=$(echo "${output_with_addr}" | sed 's/^0x[0-9a-fA-F]*: //')
 		[[ -z $output ]] && continue
 
 		# Default output (non --list):
-- 
2.34.1

[PATCH 5/7] scripts/faddr2line: Invoke addr2line as a single long-running process

[Brian Johannesmeyer]

Rather than invoking a separate addr2line process for each address, invoke
a single addr2line coprocess, and pass each address to its stdin. Previous
work [0] applied a similar change to perf, leading to a ~60x speed-up [1].

If using an object file that is _not_ vmlinux, faddr2line passes a section
name argument to addr2line. Because we do not know until runtime which
section names will be passed to addr2line, we cannot apply this change to
non-vmlinux object files. Hence, it only applies to vmlinux.

[0] commit be8ecc57f180 ("perf srcline: Use long-running addr2line per
DSO")
[1] Link:
https://eighty-twenty.org/2021/09/09/perf-addr2line-speed-improvement

Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
---
 scripts/faddr2line | 52 +++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 45 insertions(+), 7 deletions(-)

diff --git a/scripts/faddr2line b/scripts/faddr2line
index 820680c59a39..48fc8cfc80df 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -126,6 +126,48 @@ check_vmlinux() {
 	fi
 }
 
+init_addr2line() {
+	local objfile=$1
+
+	check_vmlinux
+
+	ADDR2LINE_ARGS="--functions --pretty-print --inlines --addresses --exe=$objfile"
+	if [[ $IS_VMLINUX = 1 ]]; then
+		# If the executable file is vmlinux, we don't pass section names to
+		# addr2line, so we can launch it now as a single long-running process.
+		coproc ADDR2LINE_PROC (${ADDR2LINE} ${ADDR2LINE_ARGS})
+	fi
+}
+
+run_addr2line() {
+	local addr=$1
+	local sec_name=$2
+
+	if [[ $IS_VMLINUX = 1 ]]; then
+		# We send to the addr2line process: (1) the address, then (2) a sentinel
+		# value, i.e., something that can't be interpreted as a valid address
+		# (i.e., ","). This causes addr2line to write out: (1) the answer for
+		# our address, then (2) either "?? ??:0" or "0x0...0: ..." (if
+		# using binutils' addr2line), or "," (if using LLVM's addr2line).
+		echo ${addr} >& "${ADDR2LINE_PROC[1]}"
+		echo "," >& "${ADDR2LINE_PROC[1]}"
+		local first_line
+		read -r first_line <& "${ADDR2LINE_PROC[0]}"
+		ADDR2LINE_OUT=$(echo "${first_line}" | sed 's/^0x[0-9a-fA-F]*: //')
+		while read -r line <& "${ADDR2LINE_PROC[0]}"; do
+			if [[ "$line" == "?? ??:0" ]] || [[ "$line" == "," ]] || [[ $(echo "$line" | ${GREP} "^0x00*: ") ]]; then
+				break
+			fi
+			ADDR2LINE_OUT+=$'\n'$(echo "$line" | sed 's/^0x[0-9a-fA-F]*: //')
+		done
+	else
+		# Run addr2line as a single invocation.
+		local sec_arg
+		[[ -z $sec_name ]] && sec_arg="" || sec_arg="--section=${sec_name}"
+		ADDR2LINE_OUT=$(${ADDR2LINE} ${ADDR2LINE_ARGS} ${sec_arg} ${addr} | sed 's/^0x[0-9a-fA-F]*: //')
+	fi
+}
+
 __faddr2line() {
 	local objfile=$1
 	local func_addr=$2
@@ -260,12 +302,8 @@ __faddr2line() {
 
 		# Pass section address to addr2line and strip absolute paths
 		# from the output:
-		local args="--functions --pretty-print --inlines --addresses --exe=$objfile"
-		[[ $IS_VMLINUX = 0 ]] && args="$args --section=$sec_name"
-		local output_with_addr=$(${ADDR2LINE} $args $addr | sed "s; $dir_prefix\(\./\)*; ;")
-		[[ -z $output_with_addr ]] && continue
-
-		local output=$(echo "${output_with_addr}" | sed 's/^0x[0-9a-fA-F]*: //')
+		run_addr2line $addr $sec_name
+		local output=$(echo "${ADDR2LINE_OUT}" | sed "s; $dir_prefix\(\./\)*; ;")
 		[[ -z $output ]] && continue
 
 		# Default output (non --list):
@@ -309,7 +347,7 @@ run_readelf $objfile
 
 echo "${ELF_SECHEADERS}" | ${GREP} -q '\.debug_info' || die "CONFIG_DEBUG_INFO not enabled"
 
-check_vmlinux
+init_addr2line $objfile
 
 DIR_PREFIX=supercalifragilisticexpialidocious
 find_dir_prefix $objfile
-- 
2.34.1

[PATCH 6/7] scripts/faddr2line: Remove call to addr2line from find_dir_prefix()

[Brian Johannesmeyer]

Use the single long-running faddr2line process from find_dir_prefix().

Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
---
 scripts/faddr2line | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/scripts/faddr2line b/scripts/faddr2line
index 48fc8cfc80df..1fa6beef9f97 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -85,15 +85,17 @@ command -v ${ADDR2LINE} >/dev/null 2>&1 || die "${ADDR2LINE} isn't installed"
 # init/main.c!  This only works for vmlinux.  Otherwise it falls back to
 # printing the absolute path.
 find_dir_prefix() {
-	local objfile=$1
-
 	local start_kernel_addr=$(echo "${ELF_SYMS}" | sed 's/\[.*\]//' |
 		${AWK} '$8 == "start_kernel" {printf "0x%s", $2}')
 	[[ -z $start_kernel_addr ]] && return
 
-	local file_line=$(${ADDR2LINE} -e $objfile $start_kernel_addr)
-	[[ -z $file_line ]] && return
+	run_addr2line ${start_kernel_addr} ""
+	[[ -z $ADDR2LINE_OUT ]] && return
 
+	local file_line=${ADDR2LINE_OUT#* at }
+	if [[ -z $file_line ]] || [[ $file_line = $ADDR2LINE_OUT ]]; then
+		return
+	fi
 	local prefix=${file_line%init/main.c:*}
 	if [[ -z $prefix ]] || [[ $prefix = $file_line ]]; then
 		return
@@ -350,7 +352,7 @@ echo "${ELF_SECHEADERS}" | ${GREP} -q '\.debug_info' || die "CONFIG_DEBUG_INFO n
 init_addr2line $objfile
 
 DIR_PREFIX=supercalifragilisticexpialidocious
-find_dir_prefix $objfile
+find_dir_prefix
 
 FIRST=1
 while [[ $# -gt 0 ]]; do
-- 
2.34.1

[PATCH 7/7] scripts/faddr2line: Check only two symbols when calculating symbol size

[Brian Johannesmeyer]

Rather than looping through each symbol in a particular section to
calculate a symbol's size, grep for the symbol and its immediate
successor, and only use those two symbols.

Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
---
 scripts/faddr2line | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/faddr2line b/scripts/faddr2line
index 1fa6beef9f97..70d5a4602a92 100755
--- a/scripts/faddr2line
+++ b/scripts/faddr2line
@@ -252,7 +252,7 @@ __faddr2line() {
 				found=2
 				break
 			fi
-		done < <(echo "${ELF_SYMS}" | sed 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2)
+		done < <(echo "${ELF_SYMS}" | sed 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2 | ${GREP} -A1 " ${sym_name}$")
 
 		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"
-- 
2.34.1

Re: [PATCH 7/7] scripts/faddr2line: Check only two symbols when calculating symbol size

[Brian Johannesmeyer]

On Mon, Mar 11, 2024 at 1:40 PM Brian Johannesmeyer
<bjohannesmeyer@gmail.com> wrote:
>
> Rather than looping through each symbol in a particular section to
> calculate a symbol's size, grep for the symbol and its immediate
> successor, and only use those two symbols.
>
> Signed-off-by: Brian Johannesmeyer <bjohannesmeyer@gmail.com>
> ---
>  scripts/faddr2line | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/scripts/faddr2line b/scripts/faddr2line
> index 1fa6beef9f97..70d5a4602a92 100755
> --- a/scripts/faddr2line
> +++ b/scripts/faddr2line
> @@ -252,7 +252,7 @@ __faddr2line() {
>                                 found=2
>                                 break
>                         fi
> -               done < <(echo "${ELF_SYMS}" | sed 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2)
> +               done < <(echo "${ELF_SYMS}" | sed 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2 | ${GREP} -A1 " ${sym_name}$")
>
>                 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"
> --
> 2.34.1
>

Hey Josh,

I just noticed that this patch does not correctly handle duplicate
sym_names. To fix, the "--no-group-separator" option should be added
as follows:

> -               done < <(echo "${ELF_SYMS}" | sed 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2)
> +               done < <(echo "${ELF_SYMS}" | sed 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2 | ${GREP} -A1 --no-group-separator " ${sym_name}$")

Would you like me to re-submit the patch series with this fix?

Thanks,

Brian

Re: [PATCH 7/7] scripts/faddr2line: Check only two symbols when calculating symbol size

[Josh Poimboeuf]

On Thu, Apr 11, 2024 at 12:28:29PM -0700, Brian Johannesmeyer wrote:
> Hey Josh,
> 
> I just noticed that this patch does not correctly handle duplicate
> sym_names. To fix, the "--no-group-separator" option should be added
> as follows:
> 
> > -               done < <(echo "${ELF_SYMS}" | sed 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2)
> > +               done < <(echo "${ELF_SYMS}" | sed 's/\[.*\]//' | ${AWK} -v sec=$sym_sec '$7 == sec' | sort --key=2 | ${GREP} -A1 --no-group-separator " ${sym_name}$")
> 
> Would you like me to re-submit the patch series with this fix?

Yes, that would be helpful.  Thanks!

-- 
Josh

Re: [PATCH 0/7] Improve performance of 'faddr2line'

[Josh Poimboeuf]

On Mon, Mar 11, 2024 at 09:40:12PM +0100, Brian Johannesmeyer wrote:
> Hello,
> 
> I was looking at the performance of faddr2line and noticed that it spends
> most of its time performing two tasks:
> - (1) Making redundant calls to readelf and addr2line for each address
>   (e.g., it makes 7 readelf calls and 2 addr2line calls when converting 1
> address, and it makes 252 readelf calls and 51 addr2line calls when
> converting 50 addresses); and
> - (2) Calculating a symbol’s size by unnecessarily looping through every
>   symbol in a particular section.
> 
> This patch series consists of the following parts:
> - Patches 1-2 reduce the total number of readelf calls to one,
> - Patches 3-4 make minor changes in preparation for the following patches,
> - Patches 5-6 reduce the total number of addr2line calls to one, and
> - Patch 7 modifies the symbol size calculation to only check two symbols.
> 
> I evaluated the performance of the patch series by running faddr2line with
> a standard kernel image (X86_64 defconfig with CONFIG_DEBUG_INFO enabled).
> When converting only 1 address, the patch series gives a negligible
> speedup. When converting 50 addresses, however, it gives a 15x speedup.

This looks really nice.

If testing runs ok, I'll go ahead and queue it up.

Thanks!

-- 
Josh