file ${obj} | grep -q ELF || (echo"${obj} is not an ELF file." 1>&2 ; exit 0)
# Bail out early if there isn't an __ex_table section in this object file.
objdump -hj __ex_table ${obj} 2> /dev/null > /dev/null
[ $? -ne 0 ] && exit 0
# No suspicious relocs in __ex_table, jobs a good'un
[ -z "${suspicious_relocs}" ] && exit 0
# After this point, something is seriously wrong since we just found out we # have some relocations in __ex_table which point to sections which aren't # white listed. If you're adding a new section in the Linux kernel, and # you're expecting this section to contain code which can fault (i.e. the # __ex_table relocation to your new section is expected), simply add your # new section to the white_list variable above. If not, you're probably # doing something wrong and the rest of this code is just trying to print # you more information about it.
function find_section_offset_from_symbol()
{ eval $(objdump -t ${obj} | grep ${1} | sed 's/\([0-9a-f]\+\) .\{7\} \([^ \t]\+\).*/section="\2"; section_offset="0x\1" /')
function find_symbol_and_offset_from_reloc()
{ # Extract symbol and offset from the objdump output eval $(echo $reloc | sed 's/\([^+]\+\)+\?\(0x[0-9a-f]\+\)\?/symbol="\1"; symbol_offset="\2"/')
# When the relocation points to the begining of a symbol or section, it # won't print the offset since it is zero. if [ -z "${symbol_offset}" ]; then
symbol_offset=0x0 fi
}
function find_alt_replacement_target()
{ # The target of the .altinstr_replacement is the relocation just before # the .altinstr_replacement one. eval $(objdump -rj .altinstructions ${obj} | grep -B1 "${section}+${section_offset}" | head -n1 | awk '{print $3}' |
sed 's/\([^+]\+\)+\(0x[0-9a-f]\+\)/alt_target_section="\1"; alt_target_offset="\2"/')
}
function handle_alt_replacement_reloc()
{ # This will define alt_target_section and alt_target_section_offset
find_alt_replacement_target ${section} ${section_offset}
echo"Error: found a reference to .altinstr_replacement in __ex_table:"
addr2line -fip -j ${alt_target_section} -e ${obj} ${alt_target_offset} | awk '{print "\t" $0}'
function handle_suspicious_generic_reloc()
{ if is_executable_section ${section}; then # We've got a relocation to a non white listed _executable_ # section, print a warning so the developper adds the section to # the white list or fix his code. We try to pretty-print the file # and line number where that relocation was added. echo"Warning: found a reference to section \"${section}\" in __ex_table:"
addr2line -fip -j ${section} -e ${obj} ${section_offset} | awk '{print "\t" $0}' else # Something is definitively wrong here since we've got a relocation # to a non-executable section, there's no way this would ever be # running in the kernel. echo"Error: found a reference to non-executable section \"${section}\" in __ex_table at offset ${section_offset}"
error=true fi
}
function handle_suspicious_reloc()
{
case "${section}" in ".altinstr_replacement")
handle_alt_replacement_reloc ${section} ${section_offset}
;;
*)
handle_suspicious_generic_reloc ${section} ${section_offset}
;;
esac
}
function diagnose()
{
for reloc in ${suspicious_relocs}; do # Let's find out where the target of the relocation in __ex_table # is, this will define ${symbol} and ${symbol_offset}
find_symbol_and_offset_from_reloc ${reloc}
# When there's a global symbol at the place of the relocation, # objdump will use it instead of giving us a section+offset, so # let's find out which section is this symbol in and the total # offset withing that section.
find_section_offset_from_symbol ${symbol} ${symbol_offset}
# In this case objdump was presenting us with a reloc to a symbol # rather than a section. Now that we've got the actual section, # we can skip it if it's in the white_list. if [ -z "$( echo $section | grep -v $(eval echo -e{${white_list}}))" ]; then
continue; fi
# Will either print a warning if the relocation happens to be in a # section we do not know but has executable bit set, or error out.
handle_suspicious_reloc done
}
function check_debug_info() {
objdump -hj .debug_info ${obj} 2> /dev/null > /dev/null || echo -e "${obj} does not contain debug information, the addr2line output will be limited.\n" \ "Recompile ${obj} with CONFIG_DEBUG_INFO to get a more useful output."
}
check_debug_info
diagnose
if [ "${error}" ]; then
exit 1 fi
exit 0
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