linux-kernel - [PATCH 2/3] scripts/decode_stacktrace.sh: symbol: preserve alignment

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Message-Id: <20250908-decode_strace_indent-v1-2-28e5e4758080@kernel.org>
Date: Mon, 08 Sep 2025 17:41:58 +0200
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Carlos Llamas <cmllamas@...gle.com>, 
 Elliot Berman <quic_eberman@...cinc.com>, 
 Stephen Boyd <swboyd@...omium.org>, Breno Leitao <leitao@...ian.org>, 
 Luca Ceresoli <luca.ceresoli@...tlin.com>, linux-kernel@...r.kernel.org, 
 "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
Subject: [PATCH 2/3] scripts/decode_stacktrace.sh: symbol: preserve
 alignment

With lines having a symbol to decode, the script was only trying to
preserve the alignment for the timestamps, but not the rest, nor when
the caller was set (CONFIG_PRINTK_CALLER=y).

With this sample ...

  [   52.080924] Call Trace:
  [   52.080926]  <TASK>
  [   52.080931]  dump_stack_lvl+0x6f/0xb0

... the script was producing the following output:

  [   52.080924] Call Trace:
  [   52.080926]  <TASK>
  [   52.080931] dump_stack_lvl (arch/x86/include/asm/irqflags.h:19)

  (dump_stack_lvl is no longer aligned with <TASK>: one missing space)

With this other sample ...

  [   52.080924][   T48] Call Trace:
  [   52.080926][   T48]  <TASK>
  [   52.080931][   T48]  dump_stack_lvl+0x6f/0xb0

... the script was producing the following output:

  [   52.080924][   T48] Call Trace:
  [   52.080926][   T48]  <TASK>
  [ 52.080931][ T48] dump_stack_lvl (arch/x86/include/asm/irqflags.h:19)

  (the misalignment is clearer here)

That's because the script had a workaround for CONFIG_PRINTK_TIME=y
only, see the previous comment called "Format timestamps with tabs".

To always preserve spaces, they need to be recorded along the words.
That is what is now done with the new 'spaces' array.

Some notes:

- 'extglob' is needed only for this operation, and that's why it is set
  in a dedicated subshell.

- 'read' is used with '-r' not to treat a <backslash> character in any
  special way, e.g. when followed by a space.

- When a word is removed from the 'words' array, the corresponding space
  needs to be removed from the 'spaces' array as well.

With the last sample, we now have:

  [   52.080924][   T48] Call Trace:
  [   52.080926][   T48]  <TASK>
  [   52.080931][   T48]  dump_stack_lvl (arch/x86/include/asm/irqflags.h:19)

  (the alignment is preserved)

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
 scripts/decode_stacktrace.sh | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/scripts/decode_stacktrace.sh b/scripts/decode_stacktrace.sh
index c6b5c14412f0f6f78fb60b0b042d6e22bbb46b79..0c92d6a7f777e1b2d5452dd894a13a71e3d58051 100755
--- a/scripts/decode_stacktrace.sh
+++ b/scripts/decode_stacktrace.sh
@@ -255,10 +255,11 @@ handle_line() {
 		basepath=${basepath%/init/main.c:*)}
 	fi
 
-	local words
+	local words spaces
 
-	# Tokenize
-	read -a words <<<"$1"
+	# Tokenize: words and spaces to preserve the alignment
+	read -ra words <<<"$1"
+	IFS='#' read -ra spaces <<<"$(shopt -s extglob; echo "${1//+([^[:space:]])/#}")"
 
 	# Remove hex numbers. Do it ourselves until it happens in the
 	# kernel
@@ -270,19 +271,13 @@ handle_line() {
 	for i in "${!words[@]}"; do
 		# Remove the address
 		if [[ ${words[$i]} =~ \[\<([^]]+)\>\] ]]; then
-			unset words[$i]
-		fi
-
-		# Format timestamps with tabs
-		if [[ ${words[$i]} == \[ && ${words[$i+1]} == *\] ]]; then
-			unset words[$i]
-			words[$i+1]=$(printf "[%13s\n" "${words[$i+1]}")
+			unset words[$i] spaces[$i]
 		fi
 	done
 
 	if [[ ${words[$last]} =~ ^[0-9a-f]+\] ]]; then
 		words[$last-1]="${words[$last-1]} ${words[$last]}"
-		unset words[$last]
+		unset words[$last] spaces[$last]
 		last=$(( $last - 1 ))
 	fi
 
@@ -294,7 +289,7 @@ handle_line() {
 	local info_str=""
 	if [[ ${words[$last]} =~ \([A-Z]*\) ]]; then
 		info_str=${words[$last]}
-		unset words[$last]
+		unset words[$last] spaces[$last]
 		last=$(( $last - 1 ))
 	fi
 
@@ -311,7 +306,7 @@ handle_line() {
 			modbuildid=
 		fi
 		symbol=${words[$last-1]}
-		unset words[$last-1]
+		unset words[$last-1] spaces[$last-1]
 	else
 		# The symbol is the last element, process it
 		symbol=${words[$last]}
@@ -323,7 +318,10 @@ handle_line() {
 	parse_symbol # modifies $symbol
 
 	# Add up the line number to the symbol
-	echo "${words[@]}" "${symbol}${module:+ ${module}}${info_str:+ ${info_str}}"
+	for i in "${!words[@]}"; do
+		echo -n "${spaces[i]}${words[i]}"
+	done
+	echo "${spaces[$last]}${symbol}${module:+ ${module}}${info_str:+ ${info_str}}"
 }
 
 while read line; do

-- 
2.51.0