functions: Improve TRACE_FUNC and DEBUG_STACK: provide full call stack traces in output

Signed-off-by: Thierry Laurion <insurgo@riseup.net>

initrd/etc/functions

@@ -512,25 +512,53 @@ DO_WITH_DEBUG() {
 	return "$exit_status"
 }
 
-# Trace the current script and function.
+# TRACE_FUNC outputs the function call stack in a readable format.
+# It helps debug the execution path leading to the current function.
+#
+# The format of the output is:
+#	main(/path/to/script:line) -> function1(/path/to/file:line) -> function2(/path/to/file:line)
+#
+# Usage:
+#	Call TRACE_FUNC within any function to print the call hierarchy.
 TRACE_FUNC() {
-	# Index [1] for BASH_SOURCE and FUNCNAME give us the caller location.
-	# FUNCNAME is 'main' if called from a script outside any function.
-	# BASH_LINENO is offset by 1, it provides the line that the
-	# corresponding FUNCNAME was _called from_, so BASH_LINENO[0] is the
-	# location of the caller.
-	TRACE "${BASH_SOURCE[1]}(${BASH_LINENO[0]}): ${FUNCNAME[1]}"
+	local i stack_trace=""
+
+	# Traverse the call stack from the earliest caller to the direct caller of TRACE_FUNC
+	for ((i=${#FUNCNAME[@]}-1; i>1; i--)); do 
+		stack_trace+="${FUNCNAME[i]}(${BASH_SOURCE[i]}:${BASH_LINENO[i-1]}) -> "
+	done
+
+	# Append the direct caller (without extra " -> " at the end)
+	stack_trace+="${FUNCNAME[1]}(${BASH_SOURCE[1]}:${BASH_LINENO[0]})"
+
+	# Print the final trace output
+	TRACE "${stack_trace}"
 }
 
-# Show the entire current call stack in debug output - useful if a catastrophic
-# error or something very unexpected occurs, like totally invalid parameters.
+# DEBUG_STACK prints the entire call stack for debugging purposes.
+# This function provides more detailed output than TRACE_FUNC, which is useful
+# for diagnosing errors, tracking function calls, or understanding unexpected behavior.
+#
+# The output format:
+#	call stack: (N frames)
+#	- 0 - /path/to/file(line): function_name
+#	- 1 - /path/to/file(line): function_name
+#
+# Usage:
+#	Call DEBUG_STACK anywhere to display the full stack trace.
 DEBUG_STACK() {
-	local FRAMES
-	FRAMES="${#FUNCNAME[@]}"
-	DEBUG "call stack: ($((FRAMES - 1)) frames)"
-	# Don't print DEBUG_STACK itself, start from 1
-	for i in $(seq 1 "$((FRAMES - 1))"); do
-		DEBUG "- $((i - 1)) - ${BASH_SOURCE[$i]}(${BASH_LINENO[$((i - 1))]}): ${FUNCNAME[$i]}"
+	local SKIP_FIRST=0
+
+	# If TRACE_FUNC called DEBUG_STACK, remove it from the stack to avoid redundancy.
+	[[ "${FUNCNAME[1]}" == "TRACE_FUNC" ]] && SKIP_FIRST=1  
+
+	# Get the total number of stack frames
+	local FRAMES="${#FUNCNAME[@]}"
+	DEBUG "call stack: ($((FRAMES - 1 - SKIP_FIRST)) frames)"
+
+	# Iterate through the stack and print each function call with file and line number
+	for i in $(seq $((1 + SKIP_FIRST)) "$((FRAMES - 1))"); do
+		DEBUG "- $((i - 1 - SKIP_FIRST)) - ${BASH_SOURCE[$i]}(${BASH_LINENO[$((i - 1))]}): ${FUNCNAME[$i]}"
 	done
 }