%% -*- erlang-indent-level: 2 -*-
%%% @copyright 2011-2014 Yiannis Tsiouris <[email protected]>,
%%% Chris Stavrakakis <[email protected]>,
%%% Kostis Sagonas <[email protected]>
%%% @author Yiannis Tsiouris <[email protected]>
%%% [http://www.softlab.ntua.gr/~gtsiour/]
%%% @doc This module contains functions for extracting various pieces of
%%% information from an ELF formated Object file. To fully understand
%%% the ELF format and the use of these functions please read
%%% "[http://www.linuxjournal.com/article/1060?page=0,0]" carefully.
-module(elf_format).
-export([get_tab_entries/1,
%% Relocations
get_rodata_relocs/1,
get_text_relocs/1,
extract_rela/2,
get_rela_addends/1,
%% Note
extract_note/2,
%% Executable code
extract_text/1,
%% GCC Exception Table
get_exn_handlers/1,
%% Misc.
set_architecture_flag/1,
is64bit/0
]).
-include("elf_format.hrl").
%%------------------------------------------------------------------------------
%% Types
%%------------------------------------------------------------------------------
-type elf() :: binary().
-type lp() :: non_neg_integer(). % landing pad
-type num() :: non_neg_integer().
-type index() :: non_neg_integer().
-type offset() :: non_neg_integer().
-type size() :: non_neg_integer().
-type start() :: non_neg_integer().
-type info() :: index().
-type nameoff() :: offset().
-type valueoff() :: offset().
-type name() :: string().
-type name_size() :: {name(), size()}.
-type name_sizes() :: [name_size()].
%%------------------------------------------------------------------------------
%% Abstract Data Types and Accessors for ELF Structures.
%%------------------------------------------------------------------------------
%% File header
-record(elf_ehdr, {ident, % ELF identification
type, % Object file type
machine, % Machine Type
version, % Object file version
entry, % Entry point address
phoff, % Program header offset
shoff :: offset(), % Section header offset
flags, % Processor-specific flags
ehsize :: size(), % ELF header size
phentsize :: size(), % Size of program header entry
phnum :: num(), % Number of program header entries
shentsize :: size(), % Size of section header entry
shnum :: num(), % Number of section header entries
shstrndx :: index() % Section name string table index
}).
-type elf_ehdr() :: #elf_ehdr{}.
-record(elf_ehdr_ident, {class, % File class
data, % Data encoding
version, % File version
osabi, % OS/ABI identification
abiversion, % ABI version
pad, % Start of padding bytes
nident % Size of e_ident[]
}).
%% -type elf_ehdr_ident() :: #elf_ehdr_ident{}.
%% Section header entries
-record(elf_shdr, {name, % Section name
type, % Section type
flags, % Section attributes
addr, % Virtual address in memory
offset :: offset(), % Offset in file
size :: size(), % Size of section
link, % Link to other section
info, % Miscellaneous information
addralign, % Address align boundary
entsize % Size of entries, if section has table
}).
%% -type elf_shdr() :: #elf_shdr{}.
%% Symbol table entries
-record(elf_sym, {name :: nameoff(), % Symbol name
info, % Type and Binding attributes
other, % Reserved
shndx, % Section table index
value :: valueoff(), % Symbol value
size :: size() % Size of object
}).
-type elf_sym() :: #elf_sym{}.
%% Relocations
-record(elf_rel, {r_offset :: offset(), % Address of reference
r_info :: info() % Symbol index and type of relocation
}).
-type elf_rel() :: #elf_rel{}.
-record(elf_rela, {r_offset :: offset(), % Address of reference
r_info :: info(), % Symbol index and type of relocation
r_addend :: offset() % Constant part of expression
}).
-type elf_rela() :: #elf_rela{}.
%% %% Program header table
%% -record(elf_phdr, {type, % Type of segment
%% flags, % Segment attributes
%% offset, % Offset in file
%% vaddr, % Virtual address in memory
%% paddr, % Reserved
%% filesz, % Size of segment in file
%% memsz, % Size of segment in memory
%% align % Alignment of segment
%% }).
%% %% GCC exception table
%% -record(elf_gccexntab, {lpbenc, % Landing pad base encoding
%% lpbase, % Landing pad base
%% ttenc, % Type table encoding
%% ttoff, % Type table offset
%% csenc, % Call-site table encoding
%% cstabsize, % Call-site table size
%% cstab :: cstab() % Call-site table
%% }).
%% -type elf_gccexntab() :: #elf_gccexntab{}.
-record(elf_gccexntab_callsite, {start :: start(), % Call-site start
size :: size(), % Call-site size
lp :: lp(), % Call-site landing pad
% (exception handler)
onaction % On action (e.g. cleanup)
}).
%% -type elf_gccexntab_callsite() :: #elf_gccexntab_callsite{}.
%%------------------------------------------------------------------------------
%% Accessor Functions
%%------------------------------------------------------------------------------
%% File header
%% -spec mk_ehdr(...) -> elf_ehrd().
mk_ehdr(Ident, Type, Machine, Version, Entry, Phoff, Shoff, Flags, Ehsize,
Phentsize, Phnum, Shentsize, Shnum, Shstrndx) ->
#elf_ehdr{ident = Ident, type = Type, machine = Machine, version = Version,
entry = Entry, phoff = Phoff, shoff = Shoff, flags = Flags,
ehsize = Ehsize, phentsize = Phentsize, phnum = Phnum,
shentsize = Shentsize, shnum = Shnum, shstrndx = Shstrndx}.
%% -spec ehdr_shoff(elf_ehdr()) -> offset().
%% ehdr_shoff(#elf_ehdr{shoff = Offset}) -> Offset.
%%
%% -spec ehdr_shentsize(elf_ehdr()) -> size().
%% ehdr_shentsize(#elf_ehdr{shentsize = Size}) -> Size.
%%
%% -spec ehdr_shnum(elf_ehdr()) -> num().
%% ehdr_shnum(#elf_ehdr{shnum = Num}) -> Num.
%%
%% -spec ehdr_shstrndx(elf_ehdr()) -> index().
%% ehdr_shstrndx(#elf_ehdr{shstrndx = Index}) -> Index.
%%-spec mk_ehdr_ident(...) -> elf_ehdr_ident().
mk_ehdr_ident(Class, Data, Version, OsABI, AbiVersion, Pad, Nident) ->
#elf_ehdr_ident{class = Class, data = Data, version = Version, osabi = OsABI,
abiversion = AbiVersion, pad = Pad, nident = Nident}.
%%%-------------------------
%%% Section header entries
%%%-------------------------
mk_shdr(Name, Type, Flags, Addr, Offset, Size, Link, Info, AddrAlign, EntSize) ->
#elf_shdr{name = Name, type = Type, flags = Flags, addr = Addr,
offset = Offset, size = Size, link = Link, info = Info,
addralign = AddrAlign, entsize = EntSize}.
%% -spec shdr_offset(elf_shdr()) -> offset().
%% shdr_offset(#elf_shdr{offset = Offset}) -> Offset.
%%
%% -spec shdr_size(elf_shdr()) -> size().
%% shdr_size(#elf_shdr{size = Size}) -> Size.
%%%-------------------------
%%% Symbol Table Entries
%%%-------------------------
mk_sym(Name, Info, Other, Shndx, Value, Size) ->
#elf_sym{name = Name, info = Info, other = Other,
shndx = Shndx, value = Value, size = Size}.
-spec sym_name(elf_sym()) -> nameoff().
sym_name(#elf_sym{name = Name}) -> Name.
%% -spec sym_value(elf_sym()) -> valueoff().
%% sym_value(#elf_sym{value = Value}) -> Value.
%%
%% -spec sym_size(elf_sym()) -> size().
%% sym_size(#elf_sym{size = Size}) -> Size.
%%%-------------------------
%%% Relocations
%%%-------------------------
-spec mk_rel(offset(), info()) -> elf_rel().
mk_rel(Offset, Info) ->
#elf_rel{r_offset = Offset, r_info = Info}.
%% The following two functions capitalize on the fact that the two kinds of
%% relocation records (for 32- and 64-bit architectures have similar structure.
-spec r_offset(elf_rel() | elf_rela()) -> offset().
r_offset(#elf_rel{r_offset = Offset}) -> Offset;
r_offset(#elf_rela{r_offset = Offset}) -> Offset.
-spec r_info(elf_rel() | elf_rela()) -> info().
r_info(#elf_rel{r_info = Info}) -> Info;
r_info(#elf_rela{r_info = Info}) -> Info.
-spec mk_rela(offset(), info(), offset()) -> elf_rela().
mk_rela(Offset, Info, Addend) ->
#elf_rela{r_offset = Offset, r_info = Info, r_addend = Addend}.
-spec rela_addend(elf_rela()) -> offset().
rela_addend(#elf_rela{r_addend = Addend}) -> Addend.
%% %%%-------------------------
%% %%% GCC exception table
%% %%%-------------------------
%% -type cstab() :: [elf_gccexntab_callsite()].
%%
%% mk_gccexntab(LPbenc, LPbase, TTenc, TToff, CSenc, CStabsize, CStab) ->
%% #elf_gccexntab{lpbenc = LPbenc, lpbase = LPbase, ttenc = TTenc,
%% ttoff = TToff, csenc = CSenc, cstabsize = CStabsize,
%% cstab = CStab}.
%%
%% -spec gccexntab_cstab(elf_gccexntab()) -> cstab().
%% gccexntab_cstab(#elf_gccexntab{cstab = CSTab}) -> CSTab.
mk_gccexntab_callsite(Start, Size, LP, Action) ->
#elf_gccexntab_callsite{start = Start, size=Size, lp=LP, onaction=Action}.
%% -spec gccexntab_callsite_start(elf_gccexntab_callsite()) -> start().
%% gccexntab_callsite_start(#elf_gccexntab_callsite{start = Start}) -> Start.
%%
%% -spec gccexntab_callsite_size(elf_gccexntab_callsite()) -> size().
%% gccexntab_callsite_size(#elf_gccexntab_callsite{size = Size}) -> Size.
%%
%% -spec gccexntab_callsite_lp(elf_gccexntab_callsite()) -> lp().
%% gccexntab_callsite_lp(#elf_gccexntab_callsite{lp = LP}) -> LP.
%%------------------------------------------------------------------------------
%% Functions to manipulate the ELF File Header
%%------------------------------------------------------------------------------
%% @doc Extracts the File Header from an ELF formatted object file. Also sets
%% the ELF class variable in the process dictionary (used by many functions
%% in this and hipe_llvm_main modules).
-spec extract_header(elf()) -> elf_ehdr().
extract_header(Elf) ->
Ehdr_bin = get_binary_segment(Elf, 0, ?ELF_EHDR_SIZE),
<< %% Structural pattern matching on fields.
Ident_bin:?E_IDENT_SIZE/binary,
Type:?bits(?E_TYPE_SIZE)/integer-little,
Machine:?bits(?E_MACHINE_SIZE)/integer-little,
Version:?bits(?E_VERSION_SIZE)/integer-little,
Entry:?bits(?E_ENTRY_SIZE)/integer-little,
Phoff:?bits(?E_PHOFF_SIZE)/integer-little,
Shoff:?bits(?E_SHOFF_SIZE)/integer-little,
Flags:?bits(?E_FLAGS_SIZE)/integer-little,
Ehsize:?bits(?E_EHSIZE_SIZE)/integer-little,
Phentsize:?bits(?E_PHENTSIZE_SIZE)/integer-little,
Phnum:?bits(?E_PHNUM_SIZE)/integer-little,
Shentsize:?bits(?E_SHENTSIZE_SIZE)/integer-little,
Shnum:?bits(?E_SHENTSIZE_SIZE)/integer-little,
Shstrndx:?bits(?E_SHSTRNDX_SIZE)/integer-little
>> = Ehdr_bin,
<<16#7f, $E, $L, $F, Class, Data, Version, Osabi, Abiversion,
Pad:6/binary, Nident
>> = Ident_bin,
Ident = mk_ehdr_ident(Class, Data, Version, Osabi,
Abiversion, Pad, Nident),
mk_ehdr(Ident, Type, Machine, Version, Entry, Phoff, Shoff, Flags,
Ehsize, Phentsize, Phnum, Shentsize, Shnum, Shstrndx).
%%------------------------------------------------------------------------------
%% Functions to manipulate Section Header Entries
%%------------------------------------------------------------------------------
%% @doc Extracts the Section Header Table from an ELF formated Object File.
extract_shdrtab(Elf) ->
%% Extract File Header to get info about Section Header Offset (in bytes),
%% Entry Size (in bytes) and Number of entries
#elf_ehdr{shoff = ShOff, shentsize = ShEntsize, shnum = ShNum} =
extract_header(Elf),
%% Get actual Section header table (binary)
ShdrBin = get_binary_segment(Elf, ShOff, ShNum * ShEntsize),
get_shdrtab_entries(ShdrBin, []).
get_shdrtab_entries(<<>>, Acc) ->
lists:reverse(Acc);
get_shdrtab_entries(ShdrBin, Acc) ->
<<%% Structural pattern matching on fields.
Name:?bits(?SH_NAME_SIZE)/integer-little,
Type:?bits(?SH_TYPE_SIZE)/integer-little,
Flags:?bits(?SH_FLAGS_SIZE)/integer-little,
Addr:?bits(?SH_ADDR_SIZE)/integer-little,
Offset:?bits(?SH_OFFSET_SIZE)/integer-little,
Size:?bits(?SH_SIZE_SIZE)/integer-little,
Link:?bits(?SH_LINK_SIZE)/integer-little,
Info:?bits(?SH_INFO_SIZE)/integer-little,
Addralign:?bits(?SH_ADDRALIGN_SIZE)/integer-little,
Entsize:?bits(?SH_ENTSIZE_SIZE)/integer-little,
MoreShdrE/binary
>> = ShdrBin,
ShdrE = mk_shdr(Name, Type, Flags, Addr, Offset,
Size, Link, Info, Addralign, Entsize),
get_shdrtab_entries(MoreShdrE, [ShdrE | Acc]).
%% @doc Extracts a specific Entry of a Section Header Table. This function
%% takes as argument the Section Header Table (`SHdrTab') and the entry's
%% serial number (`EntryNum') and returns the entry (`shdr').
get_shdrtab_entry(SHdrTab, EntryNum) ->
lists:nth(EntryNum + 1, SHdrTab).
%%------------------------------------------------------------------------------
%% Functions to manipulate Section Header String Table
%%------------------------------------------------------------------------------
%% @doc Extracts the Section Header String Table. This section is not a known
%% ELF Object File section. It is just a "hidden" table storing the
%% names of all sections that exist in current object file.
-spec extract_shstrtab(elf()) -> [name()].
extract_shstrtab(Elf) ->
%% Extract Section Name String Table Index
#elf_ehdr{shstrndx = ShStrNdx} = extract_header(Elf),
ShHdrTab = extract_shdrtab(Elf),
%% Extract Section header entry and get actual Section-header String Table
#elf_shdr{offset = ShStrOffset, size = ShStrSize} =
get_shdrtab_entry(ShHdrTab, ShStrNdx),
case get_binary_segment(Elf, ShStrOffset, ShStrSize) of
<<>> -> %% Segment empty
[];
ShStrTab -> %% Convert to string table
[Name || {Name, _Size} <- get_names(ShStrTab)]
end.
%%------------------------------------------------------------------------------
-spec get_tab_entries(elf()) -> [{name(), valueoff(), size()}].
get_tab_entries(Elf) ->
SymTab = extract_symtab(Elf),
Ts = [{Name, Value, Size div ?ELF_XWORD_SIZE}
|| #elf_sym{name = Name, value = Value, size = Size} <- SymTab,
Name =/= 0],
{NameIndices, ValueOffs, Sizes} = lists:unzip3(Ts),
%% Find the names of the symbols.
%% Get string table entries ([{Name, Offset in strtab section}]). Keep only
%% relevant entries:
StrTab = extract_strtab(Elf),
Relevant = [get_strtab_entry(StrTab, Off) || Off <- NameIndices],
%% Zip back to {Name, ValueOff, Size}
lists:zip3(Relevant, ValueOffs, Sizes).
%%------------------------------------------------------------------------------
%% Functions to manipulate Symbol Table
%%------------------------------------------------------------------------------
%% @doc Function that extracts Symbol Table from an ELF Object file.
extract_symtab(Elf) ->
Symtab_bin = extract_segment_by_name(Elf, ?SYMTAB),
get_symtab_entries(Symtab_bin, []).
get_symtab_entries(<<>>, Acc) ->
lists:reverse(Acc);
get_symtab_entries(Symtab_bin, Acc) ->
<<SymE_bin:?ELF_SYM_SIZE/binary, MoreSymE/binary>> = Symtab_bin,
case is64bit() of
true ->
<<%% Structural pattern matching on fields.
Name:?bits(?ST_NAME_SIZE)/integer-little,
Info:?bits(?ST_INFO_SIZE)/integer-little,
Other:?bits(?ST_OTHER_SIZE)/integer-little,
Shndx:?bits(?ST_SHNDX_SIZE)/integer-little,
Value:?bits(?ST_VALUE_SIZE)/integer-little,
Size:?bits(?ST_SIZE_SIZE)/integer-little
>> = SymE_bin;
false ->
<< %% Same fields in different order:
Name:?bits(?ST_NAME_SIZE)/integer-little,
Value:?bits(?ST_VALUE_SIZE)/integer-little,
Size:?bits(?ST_SIZE_SIZE)/integer-little,
Info:?bits(?ST_INFO_SIZE)/integer-little,
Other:?bits(?ST_OTHER_SIZE)/integer-little,
Shndx:?bits(?ST_SHNDX_SIZE)/integer-little
>> = SymE_bin
end,
SymE = mk_sym(Name, Info, Other, Shndx, Value, Size),
get_symtab_entries(MoreSymE, [SymE | Acc]).
%% @doc Extracts a specific entry from the Symbol Table (as binary).
%% This function takes as arguments the Symbol Table (`SymTab')
%% and the entry's serial number and returns that entry (`sym').
get_symtab_entry(SymTab, EntryNum) ->
lists:nth(EntryNum + 1, SymTab).
%%------------------------------------------------------------------------------
%% Functions to manipulate String Table
%%------------------------------------------------------------------------------
%% @doc Extracts String Table from an ELF formated Object File.
-spec extract_strtab(elf()) -> [{string(), offset()}].
extract_strtab(Elf) ->
Strtab_bin = extract_segment_by_name(Elf, ?STRTAB),
NamesSizes = get_names(Strtab_bin),
make_offsets(NamesSizes).
%% @doc Returns the name of the symbol at the given offset. The string table
%% contains entries of the form {Name, Offset}. If no such offset exists
%% returns the empty string (`""').
%% XXX: There might be a bug here because of the "compact" saving the ELF
%% format uses: e.g. only stores ".rela.text" for ".rela.text" and ".text".
get_strtab_entry(Strtab, Offset) ->
case lists:keyfind(Offset, 2, Strtab) of
{Name, Offset} -> Name;
false -> ""
end.
%%------------------------------------------------------------------------------
%% Functions to manipulate Relocations
%%------------------------------------------------------------------------------
%% @doc This function gets as argument an ELF binary file and returns a list
%% with all .rela.rodata labels (i.e. constants and literals in code)
%% or an empty list if no ".rela.rodata" section exists in code.
-spec get_rodata_relocs(elf()) -> [offset()].
get_rodata_relocs(Elf) ->
case is64bit() of
true ->
%% Only care about the addends (== offsets):
get_rela_addends(extract_rela(Elf, ?RODATA));
false ->
%% Find offsets hardcoded in ".rodata" entry
%%XXX: Treat all 0s as padding and skip them!
[SkipPadding || SkipPadding <- extract_rodata(Elf), SkipPadding =/= 0]
end.
-spec get_rela_addends([elf_rela()]) -> [offset()].
get_rela_addends(RelaEntries) ->
[rela_addend(E) || E <- RelaEntries].
%% @doc Extract a list of the form `[{SymbolName, Offset}]' with all relocatable
%% symbols and their offsets in the code from the ".text" section.
-spec get_text_relocs(elf()) -> [{name(), offset()}].
get_text_relocs(Elf) ->
%% Only care about the symbol table index and the offset:
NameOffsetTemp = [{?ELF_R_SYM(r_info(E)), r_offset(E)}
|| E <- extract_rela(Elf, ?TEXT)],
{NameIndices, ActualOffsets} = lists:unzip(NameOffsetTemp),
%% Find the names of the symbols:
%%
%% Get those symbol table entries that are related to Text relocs:
Symtab = extract_symtab(Elf),
SymtabEs = [get_symtab_entry(Symtab, Index) || Index <- NameIndices],
%XXX: not zero-indexed!
%% Symbol table entries contain the offset of the name of the symbol in
%% String Table:
SymtabEs2 = [sym_name(E) || E <- SymtabEs], %XXX: Do we need to sort SymtabE?
%% Get string table entries ([{Name, Offset in strtab section}]). Keep only
%% relevant entries:
Strtab = extract_strtab(Elf),
Relevant = [get_strtab_entry(Strtab, Off) || Off <- SymtabEs2],
%% Zip back with actual offsets:
lists:zip(Relevant, ActualOffsets).
%% @doc Extract the Relocations segment for section `Name' (that is passed
%% as second argument) from an ELF formated Object file binary.
-spec extract_rela(elf(), name()) -> [elf_rel() | elf_rela()].
extract_rela(Elf, Name) ->
SegName =
case is64bit() of
true -> ?RELA(Name); % ELF-64 uses ".rela"
false -> ?REL(Name) % ...while ELF-32 uses ".rel"
end,
Rela_bin = extract_segment_by_name(Elf, SegName),
get_rela_entries(Rela_bin, []).
get_rela_entries(<<>>, Acc) ->
lists:reverse(Acc);
get_rela_entries(Bin, Acc) ->
E = case is64bit() of
true ->
<<%% Structural pattern matching on fields of a Rela Entry.
Offset:?bits(?R_OFFSET_SIZE)/integer-little,
Info:?bits(?R_INFO_SIZE)/integer-little,
Addend:?bits(?R_ADDEND_SIZE)/integer-little,
Rest/binary
>> = Bin,
mk_rela(Offset, Info, Addend);
false ->
<<%% Structural pattern matching on fields of a Rel Entry.
Offset:?bits(?R_OFFSET_SIZE)/integer-little,
Info:?bits(?R_INFO_SIZE)/integer-little,
Rest/binary
>> = Bin,
mk_rel(Offset, Info)
end,
get_rela_entries(Rest, [E | Acc]).
%% %% @doc Extract the `EntryNum' (serial number) Relocation Entry.
%% get_rela_entry(Rela, EntryNum) ->
%% lists:nth(EntryNum + 1, Rela).
%%------------------------------------------------------------------------------
%% Functions to manipulate Executable Code segment
%%------------------------------------------------------------------------------
%% @doc This function gets as arguments an ELF formated binary file and
%% returns the Executable Code (".text" segment) or an empty binary if it
%% is not found.
-spec extract_text(elf()) -> binary().
extract_text(Elf) ->
extract_segment_by_name(Elf, ?TEXT).
%%------------------------------------------------------------------------------
%% Functions to manipulate Note Section
%%------------------------------------------------------------------------------
%% @doc Extract specific Note Section from an ELF Object file. The function
%% takes as first argument the object file (`Elf') and the `Name' of the
%% wanted Note Section (<b>without</b> the ".note" prefix!). It returns
%% the specified binary segment or an empty binary if no such section
%% exists.
-spec extract_note(elf(), string()) -> binary().
extract_note(Elf, Name) ->
extract_segment_by_name(Elf, ?NOTE(Name)).
%%------------------------------------------------------------------------------
%% Functions to manipulate GCC Exception Table segment
%%------------------------------------------------------------------------------
%% A description for the C++ exception table formats can be found at Exception
%% Handling Tables (http://www.codesourcery.com/cxx-abi/exceptions.pdf).
%% A list with `{Start, End, HandlerOffset}' for all call sites in the code
-spec get_exn_handlers(elf()) -> [{start(), start(), lp()}].
get_exn_handlers(Elf) ->
CallSites = extract_gccexntab_callsites(Elf),
[{Start, Start + Size, LP}
|| #elf_gccexntab_callsite{start = Start, size = Size, lp = LP} <- CallSites].
%% @doc This function gets as argument an ELF binary file and returns
%% the table (list) of call sites which is stored in GCC
%% Exception Table (".gcc_except_table") section.
%% It returns an empty list if the Exception Table is not found.
%% XXX: Assumes there is *no* Action Record Table.
extract_gccexntab_callsites(Elf) ->
case extract_segment_by_name(Elf, ?GCC_EXN_TAB) of
<<>> ->
[];
ExnTab ->
%% First byte of LSDA is Landing Pad base encoding.
<<LBenc:8, More/binary>> = ExnTab,
%% Second byte is the Landing Pad base (if its encoding is not
%% DW_EH_PE_omit) (optional).
{_LPBase, LSDACont} =
case LBenc =:= ?DW_EH_PE_omit of
true -> % No landing pad base byte. (-1 denotes that)
{-1, More};
false -> % Landing pad base.
<<Base:8, More2/binary>> = More,
{Base, More2}
end,
%% Next byte of LSDA is the encoding of the Type Table.
<<TTenc:8, More3/binary>> = LSDACont,
%% Next byte is the Types Table offset encoded in U-LEB128 (optional).
{_TTOff, LSDACont2} =
case TTenc =:= ?DW_EH_PE_omit of
true -> % There is no Types Table pointer. (-1 denotes that)
{-1, More3};
false -> % The byte offset from this field to the start of the Types
% Table used for exception matching.
leb128_decode(More3)
end,
%% Next byte of LSDA is the encoding of the fields in the Call-site Table.
<<_CSenc:8, More4/binary>> = LSDACont2,
%% Sixth byte is the size (in bytes) of the Call-site Table encoded in
%% U-LEB128.
{_CSTabSize, CSTab} = leb128_decode(More4),
%% Extract all call site information
get_gccexntab_callsites(CSTab, [])
end.
get_gccexntab_callsites(<<>>, Acc) ->
lists:reverse(Acc);
get_gccexntab_callsites(CSTab, Acc) ->
%% We are only interested in the Landing Pad of every entry.
<<Start:32/integer-little, Size:32/integer-little,
LP:32/integer-little, OnAction:8, More/binary
>> = CSTab,
GccCS = mk_gccexntab_callsite(Start, Size, LP, OnAction),
get_gccexntab_callsites(More, [GccCS | Acc]).
%%------------------------------------------------------------------------------
%% Functions to manipulate Read-only Data (.rodata)
%%------------------------------------------------------------------------------
extract_rodata(Elf) ->
Rodata_bin = extract_segment_by_name(Elf, ?RODATA),
get_rodata_entries(Rodata_bin, []).
get_rodata_entries(<<>>, Acc) ->
lists:reverse(Acc);
get_rodata_entries(Rodata_bin, Acc) ->
<<Num:?bits(?ELF_ADDR_SIZE)/integer-little, More/binary>> = Rodata_bin,
get_rodata_entries(More, [Num | Acc]).
%%------------------------------------------------------------------------------
%% Helper functions
%%------------------------------------------------------------------------------
%% @doc Returns the binary segment starting at `Offset' with length `Size'
%% (bytes) from a binary file. If `Offset' is bigger than the byte size of
%% the binary, an empty binary (`<<>>') is returned.
-spec get_binary_segment(binary(), offset(), size()) -> binary().
get_binary_segment(Bin, Offset, _Size) when Offset > byte_size(Bin) ->
<<>>;
get_binary_segment(Bin, Offset, Size) ->
<<_Hdr:Offset/binary, BinSeg:Size/binary, _More/binary>> = Bin,
BinSeg.
%% @doc This function gets as arguments an ELF formated binary object and
%% a string with the segments' name and returns the specified segment or
%% an empty binary (`<<>>') if there exists no segment with that name.
%% There are handy macros defined in elf_format.hrl for all Standard
%% Section Names.
-spec extract_segment_by_name(elf(), string()) -> binary().
extract_segment_by_name(Elf, SectionName) ->
%% Extract Section Header Table and Section Header String Table from binary
SHdrTable = extract_shdrtab(Elf),
Names = extract_shstrtab(Elf),
%% Zip to a list of (Name,ShdrE)
[_Zero | ShdrEs] = lists:keysort(2, SHdrTable), % Skip first entry (zeros).
L = lists:zip(Names, ShdrEs),
%% Find Section Header Table entry by name
case lists:keyfind(SectionName, 1, L) of
{SectionName, ShdrE} -> %% Note: Same name.
#elf_shdr{offset = Offset, size = Size} = ShdrE,
get_binary_segment(Elf, Offset, Size);
false -> %% Not found.
<<>>
end.
%% @doc Extracts a list of strings with (zero-separated) names from a binary.
%% Returns tuples of `{Name, Size}'.
%% XXX: Skip trailing 0.
-spec get_names(<<_:8,_:_*8>>) -> name_sizes().
get_names(<<0, Bin/binary>>) ->
NamesSizes = get_names(Bin, []),
fix_names(NamesSizes, []).
get_names(<<>>, Acc) ->
lists:reverse(Acc);
get_names(Bin, Acc) ->
{Name, MoreNames} = bin_get_string(Bin),
get_names(MoreNames, [{Name, length(Name)} | Acc]).
%% @doc Fix names:
%% e.g. If ".rela.text" exists, ".text" does not. Same goes for
%% ".rel.text". In that way, the Section Header String Table is more
%% compact. Add ".text" just *before* the corresponding rela-field,
%% etc.
-spec fix_names(name_sizes(), name_sizes()) -> name_sizes().
fix_names([], Acc) ->
lists:reverse(Acc);
fix_names([{Name, Size}=T | Names], Acc) ->
case is64bit() of
true ->
case string:str(Name, ".rela") =:= 1 of
true -> %% Name starts with ".rela":
Section = string:substr(Name, 6),
fix_names(Names, [{Section, Size - 5}
| [T | Acc]]); % XXX: Is order ok? (".text"
% always before ".rela.text")
false -> %% Name does not start with ".rela":
fix_names(Names, [T | Acc])
end;
false ->
case string:str(Name, ".rel") =:= 1 of
true -> %% Name starts with ".rel":
Section = string:substr(Name, 5),
fix_names(Names, [{Section, Size - 4}
| [T | Acc]]); % XXX: Is order ok? (".text"
% always before ".rela.text")
false -> %% Name does not start with ".rel":
fix_names(Names, [T | Acc])
end
end.
%% @doc A function that byte-reverses a binary. This might be needed because of
%% little (fucking!) endianess.
-spec bin_reverse(binary()) -> binary().
bin_reverse(Bin) when is_binary(Bin) ->
bin_reverse(Bin, <<>>).
-spec bin_reverse(binary(), binary()) -> binary().
bin_reverse(<<>>, Acc) ->
Acc;
bin_reverse(<<Head, More/binary>>, Acc) ->
bin_reverse(More, <<Head, Acc/binary>>).
%% @doc A function that extracts a null-terminated string from a binary. It
%% returns the found string along with the rest of the binary.
-spec bin_get_string(binary()) -> {string(), binary()}.
bin_get_string(Bin) ->
bin_get_string(Bin, <<>>).
bin_get_string(<<>>, BinAcc) ->
Bin = bin_reverse(BinAcc), % little endian!
{binary_to_list(Bin), <<>>};
bin_get_string(<<0, MoreBin/binary>>, BinAcc) ->
Bin = bin_reverse(BinAcc), % little endian!
{binary_to_list(Bin), MoreBin};
bin_get_string(<<Letter, Tail/binary>>, BinAcc) ->
bin_get_string(Tail, <<Letter, BinAcc/binary>>).
%% @doc
make_offsets(NamesSizes) ->
{Names, Sizes} = lists:unzip(NamesSizes),
Offsets = make_offsets_from_sizes(Sizes, 1, []),
lists:zip(Names, Offsets).
make_offsets_from_sizes([], _, Acc) ->
lists:reverse(Acc);
make_offsets_from_sizes([Size | Sizes], Cur, Acc) ->
make_offsets_from_sizes(Sizes, Size+Cur+1, [Cur | Acc]). % For the "."!
%% @doc Little-Endian Base 128 (LEB128) Decoder
%% This function extracts the <b>first</b> LEB128-encoded integer in a
%% binary and returns that integer along with the remaining binary. This is
%% done because a LEB128 number has variable bit-size and that is a way of
%% extracting only one number in a binary and continuing parsing the binary
%% for other kind of data (e.g. different encoding).
%% FIXME: Only decodes unsigned data!
-spec leb128_decode(binary()) -> {integer(), binary()}.
leb128_decode(LebNum) ->
leb128_decode(LebNum, 0, <<>>).
-spec leb128_decode(binary(), integer(), binary()) -> {integer(), binary()}.
leb128_decode(LebNum, NoOfBits, Acc) ->
<<Sentinel:1/bits, NextBundle:7/bits, MoreLebNums/bits>> = LebNum,
case Sentinel of
<<1:1>> -> % more bytes to follow
leb128_decode(MoreLebNums, NoOfBits+7, <<NextBundle:7/bits, Acc/bits>>);
<<0:1>> -> % byte bundle stop
Size = NoOfBits+7,
<<Num:Size/integer>> = <<NextBundle:7/bits, Acc/bits>>,
{Num, MoreLebNums}
end.
%% @doc Extract ELF Class from ELF header and export symbol to process
%% dictionary.
-spec set_architecture_flag(elf()) -> 'ok'.
set_architecture_flag(Elf) ->
%% Extract information about ELF Class from ELF Header
<<16#7f, $E, $L, $F, EI_Class, _MoreHeader/binary>>
= get_binary_segment(Elf, 0, ?ELF_EHDR_SIZE),
put(elf_class, EI_Class),
ok.
%% @doc Read from object file header if the file class is ELF32 or ELF64.
-spec is64bit() -> boolean().
is64bit() ->
case get(elf_class) of
?ELFCLASS64 -> true;
?ELFCLASS32 -> false
end.
