1#! /bin/bash
2# SPDX-License-Identifier: GPL-2.0
3# (c) 2015, Quentin Casasnovas <quentin.casasnovas@oracle.com>
4
5obj=$1
6
7file ${obj} | grep -q ELF || (echo "${obj} is not an ELF file." 1>&2 ; exit 0)
8
9# Bail out early if there isn't an __ex_table section in this object file.
10objdump -hj __ex_table ${obj} 2> /dev/null > /dev/null
11[ $? -ne 0 ] && exit 0
12
13white_list=.text,.fixup
14
15suspicious_relocs=$(objdump -rj __ex_table ${obj}  | tail -n +6 |
16			grep -v $(eval echo -e{${white_list}}) | awk '{print $3}')
17
18# No suspicious relocs in __ex_table, jobs a good'un
19[ -z "${suspicious_relocs}" ] && exit 0
20
21
22# After this point, something is seriously wrong since we just found out we
23# have some relocations in __ex_table which point to sections which aren't
24# white listed.  If you're adding a new section in the Linux kernel, and
25# you're expecting this section to contain code which can fault (i.e. the
26# __ex_table relocation to your new section is expected), simply add your
27# new section to the white_list variable above.  If not, you're probably
28# doing something wrong and the rest of this code is just trying to print
29# you more information about it.
30
31function find_section_offset_from_symbol()
32{
33    eval $(objdump -t ${obj} | grep ${1} | sed 's/\([0-9a-f]\+\) .\{7\} \([^ \t]\+\).*/section="\2"; section_offset="0x\1" /')
34
35    # addr2line takes addresses in hexadecimal...
36    section_offset=$(printf "0x%016x" $(( ${section_offset} + $2 )) )
37}
38
39function find_symbol_and_offset_from_reloc()
40{
41    # Extract symbol and offset from the objdump output
42    eval $(echo $reloc | sed 's/\([^+]\+\)+\?\(0x[0-9a-f]\+\)\?/symbol="\1"; symbol_offset="\2"/')
43
44    # When the relocation points to the begining of a symbol or section, it
45    # won't print the offset since it is zero.
46    if [ -z "${symbol_offset}" ]; then
47	symbol_offset=0x0
48    fi
49}
50
51function find_alt_replacement_target()
52{
53    # The target of the .altinstr_replacement is the relocation just before
54    # the .altinstr_replacement one.
55    eval $(objdump -rj .altinstructions ${obj} | grep -B1 "${section}+${section_offset}" | head -n1 | awk '{print $3}' |
56	   sed 's/\([^+]\+\)+\(0x[0-9a-f]\+\)/alt_target_section="\1"; alt_target_offset="\2"/')
57}
58
59function handle_alt_replacement_reloc()
60{
61    # This will define alt_target_section and alt_target_section_offset
62    find_alt_replacement_target ${section} ${section_offset}
63
64    echo "Error: found a reference to .altinstr_replacement in __ex_table:"
65    addr2line -fip -j ${alt_target_section} -e ${obj} ${alt_target_offset} | awk '{print "\t" $0}'
66
67    error=true
68}
69
70function is_executable_section()
71{
72    objdump -hwj ${section} ${obj} | grep -q CODE
73    return $?
74}
75
76function handle_suspicious_generic_reloc()
77{
78    if is_executable_section ${section}; then
79	# We've got a relocation to a non white listed _executable_
80	# section, print a warning so the developper adds the section to
81	# the white list or fix his code.  We try to pretty-print the file
82	# and line number where that relocation was added.
83	echo "Warning: found a reference to section \"${section}\" in __ex_table:"
84	addr2line -fip -j ${section} -e ${obj} ${section_offset} | awk '{print "\t" $0}'
85    else
86	# Something is definitively wrong here since we've got a relocation
87	# to a non-executable section, there's no way this would ever be
88	# running in the kernel.
89	echo "Error: found a reference to non-executable section \"${section}\" in __ex_table at offset ${section_offset}"
90	error=true
91    fi
92}
93
94function handle_suspicious_reloc()
95{
96    case "${section}" in
97	".altinstr_replacement")
98	    handle_alt_replacement_reloc ${section} ${section_offset}
99	    ;;
100	*)
101	    handle_suspicious_generic_reloc ${section} ${section_offset}
102	    ;;
103    esac
104}
105
106function diagnose()
107{
108
109    for reloc in ${suspicious_relocs}; do
110	# Let's find out where the target of the relocation in __ex_table
111	# is, this will define ${symbol} and ${symbol_offset}
112	find_symbol_and_offset_from_reloc ${reloc}
113
114	# When there's a global symbol at the place of the relocation,
115	# objdump will use it instead of giving us a section+offset, so
116	# let's find out which section is this symbol in and the total
117	# offset withing that section.
118	find_section_offset_from_symbol ${symbol} ${symbol_offset}
119
120	# In this case objdump was presenting us with a reloc to a symbol
121	# rather than a section. Now that we've got the actual section,
122	# we can skip it if it's in the white_list.
123	if [ -z "$( echo $section | grep -v $(eval echo -e{${white_list}}))" ]; then
124	    continue;
125	fi
126
127	# Will either print a warning if the relocation happens to be in a
128	# section we do not know but has executable bit set, or error out.
129	handle_suspicious_reloc
130    done
131}
132
133function check_debug_info() {
134    objdump -hj .debug_info ${obj} 2> /dev/null > /dev/null ||
135	echo -e "${obj} does not contain debug information, the addr2line output will be limited.\n" \
136	     "Recompile ${obj} with CONFIG_DEBUG_INFO to get a more useful output."
137}
138
139check_debug_info
140
141diagnose
142
143if [ "${error}" ]; then
144    exit 1
145fi
146
147exit 0
148