#! /bin/bash
# (c) 2015, Quentin Casasnovas <quentin.casasnovas@oracle.com>

global obj := $1

file $(obj) | grep -q ELF || shell {echo "$(obj) is not and 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
test $Status -ne 0 && exit 0

global white_list := '.text,.fixup'

global suspicious_relocs := $[objdump -rj __ex_table $(obj)  | tail -n +6 |
			grep -v $[eval echo -e{$(white_list)}] | awk '{print $3}]

# No suspicious relocs in __ex_table, jobs a good'un
test -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.

proc find_section_offset_from_symbol
{
    eval $[objdump -t $(obj) | grep $(1) | sed 's/\([0-9a-f]\+\) .\{7\} \([^ \t]\+\).*/section="\2"; section_offset="0x\1" /]

    # addr2line takes addresses in hexadecimal...
    global section_offset := $[printf "0x%016x" $( ${section_offset} + $2 )]
}

proc 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 test -z $(symbol_offset) {
	global symbol_offset := '0x0'
    }
}

proc 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"/]
}

proc 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}'

    global error := 'true'
}

proc is_executable_section
{
    objdump -hwj $(section) $(obj) | grep -q CODE
    return $?
}

proc handle_suspicious_generic_reloc
{
    if is_executable_section $(section) {
	# We've got a relocation to a non white listed _executable_
	# section, print a warning so the developper adds the section to
	# the white list or fix his code.  We try to pretty-print the file
	# and line number where that relocation was added.
	echo "Warning: found a reference to section \"$(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)"
	global error := 'true'
    }
}

proc handle_suspicious_reloc
{
    matchstr $(section) {
	".altinstr_replacement" {
	    handle_alt_replacement_reloc $(section) $(section_offset)
	    }
	* {
	    handle_suspicious_generic_reloc $(section) $(section_offset)
	    }
    }
}

proc diagnose
{

    for reloc in [$(suspicious_relocs)] {
	# 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 test -z $[ echo $section | grep -v $[eval echo -e{$(white_list)}]] {
	    continue;
	}

	# 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
    }
}

proc 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 test $(error) {
    exit 1
}

exit 0
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                          (C {(tail)} {(-n)} {(Lit_Other "+") (6)})
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                            {
                              (CommandSubPart
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                                left_token: <Left_CommandSub "$(">
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      op_id: Op_DAmp
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                                (SQ 
                                  <
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                                  >
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              keyword: Assign_None
              pairs: [
                (assign_pair
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                  op: Equal
                  rhs: 
                    {
                      (CommandSubPart
                        command_list: 
                          (CommandList
                            children: [
                              (C {(printf)} {(DQ ("0x%016x"))} 
                                {
                                  (ArithSubPart
                                    anode: 
                                      (ArithBinary
                                        op_id: Arith_Plus
                                        left: (ArithWord w:{(${ VSub_Name section_offset)})
                                        right: (ArithWord w:{($ VSub_Number "$2")})
                                      )
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                                }
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                    }
                  spids: [234]
                )
              ]
              spids: [234]
            )
          ]
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        )
      spids: [191 196]
    )
    (FuncDef
      name: find_symbol_and_offset_from_reloc
      body: 
        (BraceGroup
          children: [
            (C {(eval)} 
              {
                (CommandSubPart
                  command_list: 
                    (CommandList
                      children: [
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                            (C {(echo)} {($ VSub_Name "$reloc")})
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                                (SQ 
                                  <
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                          negated: False
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                        (C {(Lit_Other "[")} {(-z)} {(DQ (${ VSub_Name symbol_offset))} {(Lit_Other "]")})
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                  action: [
                    (Assignment
                      keyword: Assign_None
                      pairs: [
                        (assign_pair
                          lhs: (LhsName name:symbol_offset)
                          op: Equal
                          rhs: {(0x0)}
                          spids: [317]
                        )
                      ]
                      spids: [317]
                    )
                  ]
                  spids: [-1 314]
                )
              ]
              spids: [-1 321]
            )
          ]
          spids: [266]
        )
      spids: [260 265]
    )
    (FuncDef
      name: find_alt_replacement_target
      body: 
        (BraceGroup
          children: [
            (C {(eval)} 
              {
                (CommandSubPart
                  command_list: 
                    (CommandList
                      children: [
                        (Pipeline
                          children: [
                            (C {(objdump)} {(-rj)} {(.altinstructions)} {(${ VSub_Name obj)})
                            (C {(grep)} {(-B1)} 
                              {(DQ (${ VSub_Name section) ("+") (${ VSub_Name section_offset))}
                            )
                            (C {(head)} {(-n1)})
                            (C {(awk)} {(SQ <"{print $3}">)})
                            (C {(sed)} 
                              {
                                (SQ 
                                  <
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                                  >
                                )
                              }
                            )
                          ]
                          negated: False
                        )
                      ]
                    )
                  left_token: <Left_CommandSub "$(">
                  spids: [345 394]
                )
              }
            )
          ]
          spids: [332]
        )
      spids: [326 331]
    )
    (FuncDef
      name: handle_alt_replacement_reloc
      body: 
        (BraceGroup
          children: [
            (C {(find_alt_replacement_target)} {(${ VSub_Name section)} {(${ VSub_Name section_offset)})
            (C {(echo)} {(DQ ("Error: found a reference to .altinstr_replacement in __ex_table:"))})
            (Pipeline
              children: [
                (C {(addr2line)} {(-fip)} {(-j)} {(${ VSub_Name alt_target_section)} {(-e)} 
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                )
                (C {(awk)} {(SQ <"{print \"\\t\" $0}">)})
              ]
              negated: False
            )
            (Assignment
              keyword: Assign_None
              pairs: [(assign_pair lhs:(LhsName name:error) op:Equal rhs:{(true)} spids:[461])]
              spids: [461]
            )
          ]
          spids: [405]
        )
      spids: [399 404]
    )
    (FuncDef
      name: is_executable_section
      body: 
        (BraceGroup
          children: [
            (Pipeline
              children: [
                (C {(objdump)} {(-hwj)} {(${ VSub_Name section)} {(${ VSub_Name obj)})
                (C {(grep)} {(-q)} {(CODE)})
              ]
              negated: False
            )
            (ControlFlow token:<ControlFlow_Return return> arg_word:{($ VSub_QMark "$?")})
          ]
          spids: [473]
        )
      spids: [467 472]
    )
    (FuncDef
      name: handle_suspicious_generic_reloc
      body: 
        (BraceGroup
          children: [
            (If
              arms: [
                (if_arm
                  cond: [
                    (Sentence
                      child: (C {(is_executable_section)} {(${ VSub_Name section)})
                      terminator: <Op_Semi ";">
                    )
                  ]
                  action: [
                    (C {(echo)} 
                      {
                        (DQ ("Warning: found a reference to section ") 
                          (EscapedLiteralPart
                            token: <Lit_EscapedChar "\\\"">
                          ) (${ VSub_Name section) (EscapedLiteralPart token:<Lit_EscapedChar "\\\"">) (" in __ex_table:")
                        )
                      }
                    )
                    (Pipeline
                      children: [
                        (C {(addr2line)} {(-fip)} {(-j)} {(${ VSub_Name section)} {(-e)} 
                          {(${ VSub_Name obj)} {(${ VSub_Name section_offset)}
                        )
                        (C {(awk)} {(SQ <"{print \"\\t\" $0}">)})
                      ]
                      negated: False
                    )
                  ]
                  spids: [-1 522]
                )
              ]
              else_action: [
                (C {(echo)} 
                  {
                    (DQ ("Error: found a reference to non-executable section ") 
                      (EscapedLiteralPart token:<Lit_EscapedChar "\\\"">) (${ VSub_Name section) (EscapedLiteralPart token:<Lit_EscapedChar "\\\"">) 
                      (" in __ex_table at offset ") (${ VSub_Name section_offset)
                    )
                  }
                )
                (Assignment
                  keyword: Assign_None
                  pairs: [(assign_pair lhs:(LhsName name:error) op:Equal rhs:{(true)} spids:[614])]
                  spids: [614]
                )
              ]
              spids: [583 618]
            )
          ]
          spids: [510]
        )
      spids: [504 509]
    )
    (FuncDef
      name: handle_suspicious_reloc
      body: 
        (BraceGroup
          children: [
            (Case
              to_match: {(DQ (${ VSub_Name section))}
              arms: [
                (case_arm
                  pat_list: [{(DQ (.altinstr_replacement))}]
                  action: [
                    (C {(handle_alt_replacement_reloc)} {(${ VSub_Name section)} 
                      {(${ VSub_Name section_offset)}
                    )
                  ]
                  spids: [644 646 660 -1]
                )
                (case_arm
                  pat_list: [{(Lit_Other "*")}]
                  action: [
                    (C {(handle_suspicious_generic_reloc)} {(${ VSub_Name section)} 
                      {(${ VSub_Name section_offset)}
                    )
                  ]
                  spids: [663 664 678 -1]
                )
              ]
              spids: [632 640 681]
            )
          ]
          spids: [629]
        )
      spids: [623 628]
    )
    (FuncDef
      name: diagnose
      body: 
        (BraceGroup
          children: [
            (ForEach
              iter_name: reloc
              iter_words: [{(${ VSub_Name suspicious_relocs)}]
              do_arg_iter: False
              body: 
                (DoGroup
                  children: [
                    (C {(find_symbol_and_offset_from_reloc)} {(${ VSub_Name reloc)})
                    (C {(find_section_offset_from_symbol)} {(${ VSub_Name symbol)} 
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                    )
                    (If
                      arms: [
                        (if_arm
                          cond: [
                            (Sentence
                              child: 
                                (C {(Lit_Other "[")} {(-z)} 
                                  {
                                    (DQ 
                                      (CommandSubPart
                                        command_list: 
                                          (CommandList
                                            children: [
                                              (Pipeline
                                                children: [
                                                  (C {(echo)} {($ VSub_Name "$section")})
                                                  (C {(grep)} {(-v)} 
                                                    {
                                                      (CommandSubPart
                                                        command_list: 
                                                          (CommandList
                                                            children: [
                                                              (C {(eval)} {(echo)} 
                                                                {(-e) (Lit_LBrace "{") 
                                                                  (${ VSub_Name white_list) (Lit_RBrace "}")
                                                                }
                                                              )
                                                            ]
                                                          )
                                                        left_token: <Left_CommandSub "$(">
                                                        spids: [785 796]
                                                      )
                                                    }
                                                  )
                                                ]
                                                negated: False
                                              )
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                                          )
                                        left_token: <Left_CommandSub "$(">
                                        spids: [773 797]
                                      )
                                    )
                                  } {(Lit_Other "]")}
                                )
                              terminator: <Op_Semi ";">
                            )
                          ]
                          action: [
                            (Sentence
                              child: (ControlFlow token:<ControlFlow_Continue continue>)
                              terminator: <Op_Semi ";">
                            )
                          ]
                          spids: [-1 803]
                        )
                      ]
                      spids: [-1 810]
                    )
                    (C {(handle_suspicious_reloc)})
                  ]
                  spids: [707 825]
                )
              spids: [701 705]
            )
          ]
          spids: [692]
        )
      spids: [686 691]
    )
    (FuncDef
      name: check_debug_info
      body: 
        (BraceGroup
          children: [
            (AndOr
              children: [
                (SimpleCommand
                  words: [{(objdump)} {(-hj)} {(.debug_info)} {(${ VSub_Name obj)}]
                  redirects: [
                    (Redir
                      op_id: Redir_Great
                      fd: 2
                      arg_word: {(/dev/null)}
                      spids: [849]
                    )
                    (Redir
                      op_id: Redir_Great
                      fd: -1
                      arg_word: {(/dev/null)}
                      spids: [853]
                    )
                  ]
                )
                (C {(echo)} {(-e)} 
                  {
                    (DQ (${ VSub_Name obj) 
                      (
" does not contain debug information, the addr2line output will be limited."
                      ) (EscapedLiteralPart token:<Lit_EscapedChar "\\n">)
                    )
                  } {(DQ ("Recompile ") (${ VSub_Name obj) (" with CONFIG_DEBUG_INFO to get a more useful output."))}
                )
              ]
              op_id: Op_DPipe
            )
          ]
          spids: [836]
        )
      spids: [830 835]
    )
    (C {(check_debug_info)})
    (C {(diagnose)})
    (If
      arms: [
        (if_arm
          cond: [
            (Sentence
              child: (C {(Lit_Other "[")} {(DQ (${ VSub_Name error))} {(Lit_Other "]")})
              terminator: <Op_Semi ";">
            )
          ]
          action: [(C {(exit)} {(1)})]
          spids: [-1 904]
        )
      ]
      spids: [-1 911]
    )
    (C {(exit)} {(0)})
  ]
)