scripts: add script for translating stack dump function offsets

addr2line doesn't work with KASLR addresses.  Add a basic addr2line
wrapper script which takes the 'func+offset/size' format as input.
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

scripts/faddr2line

+#!/bin/bash
+#
+# Translate stack dump function offsets.
+#
+# addr2line doesn't work with KASLR addresses.  This works similarly to
+# addr2line, but instead takes the 'func+0x123' format as input:
+#
+#   $ ./scripts/faddr2line ~/k/vmlinux meminfo_proc_show+0x5/0x568
+#   meminfo_proc_show+0x5/0x568:
+#   meminfo_proc_show at fs/proc/meminfo.c:27
+#
+# If the address is part of an inlined function, the full inline call chain is
+# printed:
+#
+#   $ ./scripts/faddr2line ~/k/vmlinux native_write_msr+0x6/0x27
+#   native_write_msr+0x6/0x27:
+#   arch_static_branch at arch/x86/include/asm/msr.h:121
+#    (inlined by) static_key_false at include/linux/jump_label.h:125
+#    (inlined by) native_write_msr at arch/x86/include/asm/msr.h:125
+#
+# The function size after the '/' in the input is optional, but recommended.
+# It's used to help disambiguate any duplicate symbol names, which can occur
+# rarely.  If the size is omitted for a duplicate symbol then it's possible for
+# multiple code sites to be printed:
+#
+#   $ ./scripts/faddr2line ~/k/vmlinux raw_ioctl+0x5
+#   raw_ioctl+0x5/0x20:
+#   raw_ioctl at drivers/char/raw.c:122
+#
+#   raw_ioctl+0x5/0xb1:
+#   raw_ioctl at net/ipv4/raw.c:876
+#
+# Multiple addresses can be specified on a single command line:
+#
+#   $ ./scripts/faddr2line ~/k/vmlinux type_show+0x10/45 free_reserved_area+0x90
+#   type_show+0x10/0x2d:
+#   type_show at drivers/video/backlight/backlight.c:213
+#
+#   free_reserved_area+0x90/0x123:
+#   free_reserved_area at mm/page_alloc.c:6429 (discriminator 2)
+
+
+set -o errexit
+set -o nounset
+
+command -v awk >/dev/null 2>&1 || die "awk isn't installed"
+command -v readelf >/dev/null 2>&1 || die "readelf isn't installed"
+command -v addr2line >/dev/null 2>&1 || die "addr2line isn't installed"
+
+usage() {
+	echo "usage: faddr2line <object file> <func+offset> <func+offset>..." >&2
+	exit 1
+}
+
+warn() {
+	echo "$1" >&2
+}
+
+die() {
+	echo "ERROR: $1" >&2
+	exit 1
+}
+
+# Try to figure out the source directory prefix so we can remove it from the
+# addr2line output.  HACK ALERT: This assumes that start_kernel() is in
+# kernel/init.c!  This only works for vmlinux.  Otherwise it falls back to
+# printing the absolute path.
+find_dir_prefix() {
+	local objfile=$1
+
+	local start_kernel_addr=$(readelf -sW $objfile | awk '$8 == "start_kernel" {printf "0x%s", $2}')
+	[[ -z $start_kernel_addr ]] && return
+
+	local file_line=$(addr2line -e $objfile $start_kernel_addr)
+	[[ -z $file_line ]] && return
+
+	local prefix=${file_line%init/main.c:*}
+	if [[ -z $prefix ]] || [[ $prefix = $file_line ]]; then
+		return
+	fi
+
+	DIR_PREFIX=$prefix
+	return 0
+}
+
+__faddr2line() {
+	local objfile=$1
+	local func_addr=$2
+	local dir_prefix=$3
+	local print_warnings=$4
+
+	local func=${func_addr%+*}
+	local offset=${func_addr#*+}
+	offset=${offset%/*}
+	local size=
+	[[ $func_addr =~ "/" ]] && size=${func_addr#*/}
+
+	if [[ -z $func ]] || [[ -z $offset ]] || [[ $func = $func_addr ]]; then
+		warn "bad func+offset $func_addr"
+		DONE=1
+		return
+	fi
+
+	# Go through each of the object's symbols which match the func name.
+	# In rare cases there might be duplicates.
+	while read symbol; do
+		local fields=($symbol)
+		local sym_base=0x${fields[1]}
+		local sym_size=${fields[2]}
+		local sym_type=${fields[3]}
+
+		# calculate the address
+		local addr=$(($sym_base + $offset))
+		if [[ -z $addr ]] || [[ $addr = 0 ]]; then
+			warn "bad address: $sym_base + $offset"
+			DONE=1
+			return
+		fi
+		local hexaddr=0x$(printf %x $addr)
+
+		# weed out non-function symbols
+		if [[ $sym_type != "FUNC" ]]; then
+			[[ $print_warnings = 1 ]] &&
+				echo "skipping $func address at $hexaddr due to non-function symbol"
+			continue
+		fi
+
+		# if the user provided a size, make sure it matches the symbol's size
+		if [[ -n $size ]] && [[ $size -ne $sym_size ]]; then
+			[[ $print_warnings = 1 ]] &&
+				echo "skipping $func address at $hexaddr due to size mismatch ($size != $sym_size)"
+			continue;
+		fi
+
+		# make sure the provided offset is within the symbol's range
+		if [[ $offset -gt $sym_size ]]; then
+			[[ $print_warnings = 1 ]] &&
+				echo "skipping $func address at $hexaddr due to size mismatch ($offset > $sym_size)"
+			continue
+		fi
+
+		# separate multiple entries with a blank line
+		[[ $FIRST = 0 ]] && echo
+		FIRST=0
+
+		local hexsize=0x$(printf %x $sym_size)
+		echo "$func+$offset/$hexsize:"
+		addr2line -fpie $objfile $hexaddr | sed "s;$dir_prefix;;"
+		DONE=1
+
+	done < <(readelf -sW $objfile | awk -v f=$func '$8 == f {print}')
+}
+
+[[ $# -lt 2 ]] && usage
+
+objfile=$1
+[[ ! -f $objfile ]] && die "can't find objfile $objfile"
+shift
+
+DIR_PREFIX=supercalifragilisticexpialidocious
+find_dir_prefix $objfile
+
+FIRST=1
+while [[ $# -gt 0 ]]; do
+	func_addr=$1
+	shift
+
+	# print any matches found
+	DONE=0
+	__faddr2line $objfile $func_addr $DIR_PREFIX 0
+
+	# if no match was found, print warnings
+	if [[ $DONE = 0 ]]; then
+		__faddr2line $objfile $func_addr $DIR_PREFIX 1
+		warn "no match for $func_addr"
+	fi
+done