scripts/faddr2line: Reduce number of readelf calls to three

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>
Link: https://lore.kernel.org/r/20240415145538.1938745-2-bjohannesmeyer@gmail.comSigned-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

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