scripts/faddr2line: Combine three readelf calls into one

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>
Link: https://lore.kernel.org/r/20240415145538.1938745-3-bjohannesmeyer@gmail.comSigned-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

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() {