1 #! /bin/bash
2 # SPDX-License-Identifier: GPL-2.0
3 # (c) 2015, Quentin Casasnovas <quentin.casasnovas@oracle.com>
4
5 obj=$1
6
7 file ${obj} | grep -q ELF || (echo "${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.
10 objdump -hj __ex_table ${obj} 2> /dev/null > /dev/null
11 [ $? -ne 0 ] && exit 0
12
13 white_list=.text,.fixup
14
15 suspicious_relocs=$(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
31 function 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
39 function 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
51 function 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
59 function 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
70 function is_executable_section()
71 {
72 objdump -hwj ${section} ${obj} | grep -q CODE
73 return $?
74 }
75
76 function 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 ${section_offset}"
90 error=true
91 fi
92 }
93
94 function handle_suspicious_reloc()
95 {
96 case "${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
106 function 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
133 function 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 ${obj} with CONFIG_DEBUG_INFO to get a more useful output."
137 }
138
139 check_debug_info
140
141 diagnose
142
143 if [ "${error}" ]; then
144 exit 1
145 fi
146
147 exit 0
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