aboutsummaryrefslogblamecommitdiffstats
path: root/lib/compiler/src/beam_disasm.erl
blob: 5c4d8e12b5ca7af923f53474ae79c35dff1cd582 (plain) (tree)
1
2
3
4
5
6
7
8
9
10
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623

                   
  
                                                        
  




                                                                      
  



                                                                         
  





























































































































































































                                                                              
                                                    































































































































































































































































































































































































































                                                                                    
                                                             







                                                         


















































































































































































































































































































































































                                                                                  






                                                          



                                                           




















































































                                                                                 







                                        

















































                                                                            
%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2000-2011. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%=======================================================================
%% Notes:
%%   1. It does NOT work for .beam files of previous BEAM versions.
%%   2. If handling of new BEAM instructions is needed, this should be 
%%      inserted at the end of function resolve_inst().
%%=======================================================================

-module(beam_disasm).

-export([file/1]). %% the main function
-export([function__code/1, format_error/1]).
-ifdef(DEBUG_DISASM).
-export([dfs/1, df/1, files/1, pp/1, pp/2]).
-endif.

-author("Kostis Sagonas").

-include("beam_opcodes.hrl").
-include("beam_disasm.hrl").

%%-----------------------------------------------------------------------

-type literals()     :: 'none' | gb_tree().
-type symbolic_tag() :: 'a' | 'f' | 'h' | 'i' | 'u' | 'x' | 'y' | 'z'.
-type disasm_tag()   :: symbolic_tag() | 'fr' | 'atom' | 'float' | 'literal'.
-type disasm_term()  :: 'nil' | {disasm_tag(), _}.

%%-----------------------------------------------------------------------

-define(NO_DEBUG(Str,Xs), ok).
-define(DEBUG(Str,Xs), io:format(Str,Xs)).
-define(exit(Reason), exit({?MODULE,?LINE,Reason})).

%%-----------------------------------------------------------------------
%% Utility functions to get/set their fields. (Uncomment and export
%% them when/if they get used in other files.)
%%-----------------------------------------------------------------------

%% -spec function__name(#function{}) -> atom().
%% function__name(#function{name = N}) -> N.
%% -spec function__arity(#function{}) -> arity().
%% function__arity(#function{arity = A}) -> A.
%% function__entry(#function{entry = E}) -> E.

-spec function__code(#function{}) -> [beam_instr()].
function__code(#function{code = Code}) -> Code.

-spec function__code_update(#function{}, [beam_instr()]) -> #function{}.
function__code_update(Function, NewCode) ->
  Function#function{code = NewCode}.

%%-----------------------------------------------------------------------
%% Error information

-spec format_error({'internal',term()} | {'error',atom(),term()}) -> string().

format_error({internal,Error}) ->
    io_lib:format("~p: disassembly failed with reason ~P.",
		  [?MODULE, Error, 25]);
format_error({error,Module,Error}) ->
    lists:flatten(Module:format_error(Error)).

%%-----------------------------------------------------------------------
%% User comfort functions to directly disassemble to file or to
%% stream, pretty-printed, and to just pretty-print, also commented.
%%-----------------------------------------------------------------------

-ifdef(DEBUG_DISASM).

dfs(Files) when is_list(Files) ->
    lists:foreach(fun df/1, Files).

df(Module) when is_atom(Module) ->
    case code:which(Module) of
	File when is_list(File) ->
	    df(File);
	Reason when is_atom(Reason) ->
	    {error,?MODULE,Reason}
    end;
df(File) when is_list(File) ->
    file(File, filename:rootname(File, ".beam")++".dis").

files(Files) when is_list(Files) ->
    lists:foreach(fun (File) -> file(File, group_leader()) end, Files).

file(File, Dest) ->
    case file(File) of
	#beam_file{code = DisasmCode} ->
	    pp(Dest, [{file,File}, {code,DisasmCode}]);
	Error -> Error
    end.

-spec pp([_]) -> 'ok' | {'error', atom()}.

pp(Disasm) ->
    pp(group_leader(), Disasm).

-spec pp(pid() | file:filename(), [_]) -> 'ok' | {'error', atom()}.

pp(Stream, Disasm) when is_pid(Stream), is_list(Disasm) ->
    NL = io_lib:nl(),
    lists:foreach(
      fun ({code,Code}) ->
	      lists:foreach(
		fun (#function{name=F,arity=A,entry=E,code=C}) ->
			io:format(Stream, "~p.~n", [{function,F,A,E}]),
			lists:foreach(
			  fun (I) -> 
				  io:put_chars(Stream, [pp_instr(I)|NL])
			  end, C),
			io:nl(Stream)
		end, Code);
	  (Item) ->
	      io:format(Stream, "~p.~n~n", [Item])
      end, Disasm),
    ok;
pp(File, Disasm) when is_list(Disasm) ->
    case file:open(File, [write]) of
	{ok,F} ->
	    Result = pp(F, Disasm),
	    ok = file:close(F),
	    Result;
	{error,_Reason} = Error -> Error
    end.

pp_instr({comment,I,Comment}) ->
    [pp_instr(I)|" % "++Comment];
pp_instr({comment,Comment}) ->
    ["%% "++Comment];
pp_instr({label,_}=I) ->
    io_lib:format("  ~p.", [I]);
pp_instr(I) ->
    io_lib:format("    ~p.", [I]).

-endif.

%%-----------------------------------------------------------------------
%% The main exported function
%%   File is either a file name or a binary containing the code.
%%   Call `format_error({error, Module, Reason})' for an error string.
%%-----------------------------------------------------------------------

-spec file(file:filename() | binary()) -> #beam_file{} | {'error',atom(),_}.

file(File) ->
    try process_chunks(File)
    catch error:Reason ->
	    {error,?MODULE,{internal,{Reason,erlang:get_stacktrace()}}}
    end.

%%-----------------------------------------------------------------------
%% Interface might need to be revised -- do not depend on it.
%%-----------------------------------------------------------------------

process_chunks(F) ->
    case beam_lib:chunks(F, [atoms,"Code","StrT",
			     indexed_imports,labeled_exports]) of
	{ok,{Module,
	     [{atoms,AtomsList},{"Code",CodeBin},{"StrT",StrBin},
	      {indexed_imports,ImportsList},{labeled_exports,Exports}]}} ->
	    Atoms = mk_atoms(AtomsList),
	    LambdaBin = optional_chunk(F, "FunT"),
	    Lambdas = beam_disasm_lambdas(LambdaBin, Atoms),
	    LiteralBin = optional_chunk(F, "LitT"),
	    Literals = beam_disasm_literals(LiteralBin),
	    Code = beam_disasm_code(CodeBin, Atoms, mk_imports(ImportsList),
				    StrBin, Lambdas, Literals, Module),
	    Attributes = optional_chunk(F, attributes),
	    CompInfo = 
		case optional_chunk(F, "CInf") of
		    none -> none;
		    CompInfoBin when is_binary(CompInfoBin) ->
			binary_to_term(CompInfoBin)
		end,
	    #beam_file{module = Module,
		       labeled_exports = Exports,
		       attributes = Attributes,
		       compile_info = CompInfo,
		       code = Code};
	Error -> Error
    end.

%%-----------------------------------------------------------------------
%% Retrieve an optional chunk or none if the chunk doesn't exist.
%%-----------------------------------------------------------------------

optional_chunk(F, ChunkTag) ->
    case beam_lib:chunks(F, [ChunkTag]) of
	{ok,{_Module,[{ChunkTag,Chunk}]}} -> Chunk;
	{error,beam_lib,{missing_chunk,_,_}} -> none
    end.

%%-----------------------------------------------------------------------
%% Disassembles the lambda (fun) table of a BEAM file.
%%-----------------------------------------------------------------------

-type l_info() :: {non_neg_integer(), {_,_,_,_,_,_}}.
-spec beam_disasm_lambdas('none' | binary(), gb_tree()) -> 'none' | [l_info()].

beam_disasm_lambdas(none, _) -> none;
beam_disasm_lambdas(<<_:32,Tab/binary>>, Atoms) ->
    disasm_lambdas(Tab, Atoms, 0).

disasm_lambdas(<<F:32,A:32,Lbl:32,Index:32,NumFree:32,OldUniq:32,More/binary>>,
	       Atoms, OldIndex) ->
    Info = {lookup(F, Atoms),A,Lbl,Index,NumFree,OldUniq},
    [{OldIndex,Info}|disasm_lambdas(More, Atoms, OldIndex+1)];
disasm_lambdas(<<>>, _, _) -> [].

%%-----------------------------------------------------------------------
%% Disassembles the literal table (constant pool) of a BEAM file.
%%-----------------------------------------------------------------------

-spec beam_disasm_literals('none' | binary()) -> literals().

beam_disasm_literals(none) -> none;
beam_disasm_literals(<<_:32,Compressed/binary>>) ->
    <<_:32,Tab/binary>> = zlib:uncompress(Compressed),
    gb_trees:from_orddict(disasm_literals(Tab, 0)).

disasm_literals(<<Sz:32,Ext:Sz/binary,T/binary>>, Index) ->
    [{Index,binary_to_term(Ext)}|disasm_literals(T, Index+1)];
disasm_literals(<<>>, _) -> [].

%%-----------------------------------------------------------------------
%% Disassembles the code chunk of a BEAM file:
%%   - The code is first disassembled into a long list of instructions.
%%   - This list is then split into functions and all names are resolved.
%%-----------------------------------------------------------------------

beam_disasm_code(<<_SS:32, % Sub-Size (length of information before code)
		  _IS:32,  % Instruction Set Identifier (always 0)
		  _OM:32,  % Opcode Max
		  _L:32,_F:32,
		  CodeBin/binary>>, Atoms, Imports,
		 Str, Lambdas, Literals, M) ->
    Code = binary_to_list(CodeBin),
    try disasm_code(Code, Atoms, Literals) of
	DisasmCode ->
	    Functions = get_function_chunks(DisasmCode),
	    Labels = mk_labels(local_labels(Functions)),
	    [function__code_update(Function,
				   resolve_names(Is, Imports, Str,
						 Labels, Lambdas, Literals, M))
	     || Function = #function{code=Is} <- Functions]
    catch
	error:Rsn ->
	    ?NO_DEBUG('code disassembling failed: ~p~n', [Rsn]),
	    ?exit(Rsn)
    end.

%%-----------------------------------------------------------------------

disasm_code([B|Bs], Atoms, Literals) ->
    {Instr,RestBs} = disasm_instr(B, Bs, Atoms, Literals),
    [Instr|disasm_code(RestBs, Atoms, Literals)];
disasm_code([], _, _) -> [].

%%-----------------------------------------------------------------------
%% Splits the code stream into chunks representing the code of functions.
%%
%% NOTE: code actually looks like
%%   label L1: ... label Ln:
%%     func_info ...
%%   label entry:
%%     ...
%%     <on failure, use label Li to show where things died>
%%     ...
%% So the labels before each func_info should be included as well.
%% Ideally, only one such label is needed, but the BEAM compiler
%% before R8 didn't care to remove the redundant ones.
%%-----------------------------------------------------------------------

get_function_chunks([]) ->
    ?exit(empty_code_segment);
get_function_chunks(Code) ->
    get_funs(labels_r(Code, [])).

labels_r([], R) -> {R, []};
labels_r([{label,_}=I|Is], R) ->
    labels_r(Is, [I|R]);
labels_r(Is, R) -> {R, Is}.

get_funs({[],[]}) -> [];
get_funs({_,[]}) ->
    ?exit(no_func_info_in_code_segment);
get_funs({LsR0,[{func_info,[{atom,M}=AtomM,{atom,F}=AtomF,ArityArg]}|Code0]})
  when is_atom(M), is_atom(F) ->
    Arity = resolve_arg_unsigned(ArityArg),
    {LsR,Code,RestCode} = get_fun(Code0, []),
    Entry = case Code of
		[{label,[{u,E}]}|_] -> E;
		_ -> undefined
	    end,
    [#function{name=F,
	       arity=Arity,
	       entry=Entry,
	       code=lists:reverse(LsR0, [{func_info,AtomM,AtomF,Arity}|Code])}
     |get_funs({LsR,RestCode})].

get_fun([{func_info,_}|_]=Is, R0) ->
    {LsR,R} = labels_r(R0, []),
    {LsR,lists:reverse(R),Is};
get_fun([{int_code_end,[]}], R) ->
    {[],lists:reverse(R),[]};
get_fun([I|Is], R) ->
    get_fun(Is, [I|R]);
get_fun([], R) ->
    ?DEBUG('warning: code segment did not end with int_code_end~n',[]),
    {[],lists:reverse(R),[]}.

%%-----------------------------------------------------------------------
%% Collects local labels -- I am not sure this is 100% what is needed.
%%-----------------------------------------------------------------------

local_labels(Funs) ->
    lists:sort(lists:foldl(fun (F, R) ->
				   local_labels_1(function__code(F), R)
			   end, [], Funs)).

%% The first clause below attempts to provide some (limited form of)
%% backwards compatibility; it is not needed for .beam files generated
%% by the R8 compiler.  The clause should one fine day be taken out.
local_labels_1([{label,_}|[{label,_}|_]=Code], R) ->
    local_labels_1(Code, R);
local_labels_1([{label,_},{func_info,{atom,M},{atom,F},A}|Code], R)
  when is_atom(M), is_atom(F) ->
    local_labels_2(Code, R, M, F, A);
local_labels_1(Code, _) ->
    ?exit({'local_labels: no label in code',Code}).

local_labels_2([{label,[{u,L}]}|Code], R, M, F, A) ->
    local_labels_2(Code, [{L,{M,F,A}}|R], M, F, A);
local_labels_2(_, R, _, _, _) -> R.

%%-----------------------------------------------------------------------
%% Disassembles a single BEAM instruction; most instructions are handled
%% in a generic way; indexing instructions are handled separately.
%%-----------------------------------------------------------------------

disasm_instr(B, Bs, Atoms, Literals) ->
    {SymOp, Arity} = beam_opcodes:opname(B),
    case SymOp of
	select_val ->
	    disasm_select_inst(select_val, Bs, Atoms, Literals);
	select_tuple_arity ->
	    disasm_select_inst(select_tuple_arity, Bs, Atoms, Literals);
	_ ->
	    try decode_n_args(Arity, Bs, Atoms, Literals) of
		{Args, RestBs} ->
		    ?NO_DEBUG("instr ~p~n", [{SymOp, Args}]),
		    {{SymOp, Args}, RestBs}
	    catch
		error:Rsn ->
		    ?NO_DEBUG("decode_n_args(~p,~p) failed~n", [Arity, Bs]),
		    ?exit({cannot_disasm_instr, {SymOp, Arity, Rsn}})
	    end
    end.

%%-----------------------------------------------------------------------
%% Disassembles a BEAM select_* instruction used for indexing.
%%   Currently handles {select_val,3} and {select_tuple_arity,3} insts.
%%
%%   The arguments of a "select"-type instruction look as follows:
%%       <reg>, {f,FailLabel}, {list, <num cases>, [<case1> ... <caseN>]}
%%   where each case is of the form [symbol,{f,Label}].
%%-----------------------------------------------------------------------

disasm_select_inst(Inst, Bs, Atoms, Literals) ->
    {X, Bs1} = decode_arg(Bs, Atoms, Literals),
    {F, Bs2} = decode_arg(Bs1, Atoms, Literals),
    {Z, Bs3} = decode_arg(Bs2, Atoms, Literals),
    {U, Bs4} = decode_arg(Bs3, Atoms, Literals),
    {u, Len} = U,
    {List, RestBs} = decode_n_args(Len, Bs4, Atoms, Literals),
    {{Inst, [X,F,{Z,U,List}]}, RestBs}.

%%-----------------------------------------------------------------------
%% decode_arg([Byte]) -> {Arg, [Byte]}
%%
%% - an arg can have variable length, so we must return arg + remaining bytes
%% - decodes an argument into its 'raw' form: { Tag, Value }
%%   several types map to a single tag, so the byte code instr must then
%%   assign a type to it
%%-----------------------------------------------------------------------

-spec decode_arg([byte(),...]) -> {{disasm_tag(),_}, [byte()]}.

decode_arg([B|Bs]) ->
    Tag = decode_tag(B band 2#111),
    ?NO_DEBUG('Tag = ~p, B = ~p, Bs = ~p~n', [Tag, B, Bs]),
    case Tag of
	z ->
	    decode_z_tagged(Tag, B, Bs, no_literals);
	_ ->
	    %% all other cases are handled as if they were integers
	    decode_int(Tag, B, Bs)
    end.

-spec decode_arg([byte(),...], gb_tree(), literals()) -> {disasm_term(), [byte()]}.

decode_arg([B|Bs0], Atoms, Literals) ->
    Tag = decode_tag(B band 2#111),
    ?NO_DEBUG('Tag = ~p, B = ~p, Bs = ~p~n', [Tag, B, Bs]),
    case Tag of
	z ->
	    decode_z_tagged(Tag, B, Bs0, Literals);
	a ->
	    %% atom or nil
	    case decode_int(Tag, B, Bs0) of
		{{a,0},Bs} -> {nil,Bs};
		{{a,I},Bs} -> {{atom,lookup(I, Atoms)},Bs}
	    end;
	_ ->
	    %% all other cases are handled as if they were integers
	    decode_int(Tag, B, Bs0)
    end.

%%-----------------------------------------------------------------------
%% Decodes an integer value.  Handles positives, negatives, and bignums.
%%
%% Tries to do the opposite of:
%%   beam_asm:encode(1, 5) =            [81]
%%   beam_asm:encode(1, 1000) =         [105,232]
%%   beam_asm:encode(1, 2047) =         [233,255]
%%   beam_asm:encode(1, 2048) =         [25,8,0]
%%   beam_asm:encode(1,-1) =            [25,255,255]
%%   beam_asm:encode(1,-4294967295) =   [121,255,0,0,0,1]
%%   beam_asm:encode(1, 4294967295) =   [121,0,255,255,255,255]
%%   beam_asm:encode(1, 429496729501) = [121,99,255,255,255,157]
%%-----------------------------------------------------------------------

decode_int(Tag,B,Bs) when (B band 16#08) =:= 0 ->
    %% N < 16 = 4 bits, NNNN:0:TTT
    N = B bsr 4,
    {{Tag,N},Bs};
decode_int(Tag,B,Bs) when (B band 16#10) =:= 0 ->
    %% N < 2048 = 11 bits = 3:8 bits, NNN:01:TTT, NNNNNNNN
    [B1|Bs1] = Bs,
    Val0 = B band 2#11100000,
    N = (Val0 bsl 3) bor B1,
    ?NO_DEBUG('NNN:01:TTT, NNNNNNNN = ~n~p:01:~p, ~p = ~p~n', [Val0,Tag,B,N]),
    {{Tag,N},Bs1};
decode_int(Tag,B,Bs) ->
    {Len,Bs1} = decode_int_length(B,Bs),
    {IntBs,RemBs} = take_bytes(Len,Bs1),
    N = build_arg(IntBs),
    [F|_] = IntBs,
    Num = if F > 127, Tag =:= i -> decode_negative(N,Len);
	     true -> N
	  end,
    ?NO_DEBUG('Len = ~p, IntBs = ~p, Num = ~p~n', [Len,IntBs,Num]),
    {{Tag,Num},RemBs}.

-spec decode_int_length(integer(), [byte()]) -> {integer(), [byte()]}.

decode_int_length(B, Bs) ->
    %% The following imitates get_erlang_integer() in beam_load.c
    %% Len is the size of the integer value in bytes
    case B bsr 5 of
	7 ->
	    {Arg,ArgBs} = decode_arg(Bs),
	    case Arg of
		{u,L} ->
		    {L+9,ArgBs};  % 9 stands for 7+2
		_ -> 
		    ?exit({decode_int,weird_bignum_sublength,Arg})
	    end;
	L ->
	    {L+2,Bs}
    end.
    
-spec decode_negative(non_neg_integer(), non_neg_integer()) -> neg_integer().

decode_negative(N, Len) ->
    N - (1 bsl (Len*8)). % 8 is number of bits in a byte

%%-----------------------------------------------------------------------
%% Decodes lists and floating point numbers.
%%-----------------------------------------------------------------------

decode_z_tagged(Tag,B,Bs,Literals) when (B band 16#08) =:= 0 ->
    N = B bsr 4,
    case N of
	0 -> % float
	    decode_float(Bs);
	1 -> % list
	    {{Tag,N},Bs};
	2 -> % fr
	    decode_fr(Bs);
	3 -> % allocation list
	    decode_alloc_list(Bs, Literals);
	4 -> % literal
	    {{u,LitIndex},RestBs} = decode_arg(Bs),
	    {{literal,gb_trees:get(LitIndex, Literals)},RestBs};
	_ ->
	    ?exit({decode_z_tagged,{invalid_extended_tag,N}})
    end;
decode_z_tagged(_,B,_,_) ->
    ?exit({decode_z_tagged,{weird_value,B}}).

-spec decode_float([byte(),...]) -> {{'float', float()}, [byte()]}.

decode_float(Bs) ->
    {FL,RestBs} = take_bytes(8,Bs),
    <<Float:64/float>> = list_to_binary(FL),
    {{float,Float},RestBs}.

-spec decode_fr([byte(),...]) -> {{'fr', non_neg_integer()}, [byte()]}.

decode_fr(Bs) ->
    {{u,Fr},RestBs} = decode_arg(Bs),
    {{fr,Fr},RestBs}.

decode_alloc_list(Bs, Literals) ->
    {{u,N},RestBs} = decode_arg(Bs),
    decode_alloc_list_1(N, Literals, RestBs, []).

decode_alloc_list_1(0, _Literals, RestBs, Acc) ->
    {{u,{alloc,lists:reverse(Acc)}},RestBs};
decode_alloc_list_1(N, Literals, Bs0, Acc) ->
    {{u,Type},Bs1} = decode_arg(Bs0),
    {{u,Val},Bs} = decode_arg(Bs1),
    Res = case Type of
	      0 -> {words,Val};
	      1 -> {floats,Val};
	      2 -> {literal,gb_trees:get(Val, Literals)}
	  end,
    decode_alloc_list_1(N-1, Literals, Bs, [Res|Acc]).

%%-----------------------------------------------------------------------
%% take N bytes from a stream, return {Taken_bytes, Remaining_bytes}
%%-----------------------------------------------------------------------

-spec take_bytes(non_neg_integer(), [byte()]) -> {[byte()], [byte()]}.

take_bytes(N, Bs) ->
    take_bytes(N, Bs, []).

take_bytes(N, [B|Bs], Acc) when N > 0 ->
    take_bytes(N-1, Bs, [B|Acc]);
take_bytes(0, Bs, Acc) ->
    {lists:reverse(Acc), Bs}.

%%-----------------------------------------------------------------------
%% from a list of bytes Bn,Bn-1,...,B1,B0
%% build  (Bn << 8*n) bor ... bor (B1 << 8) bor (B0 << 0)
%%-----------------------------------------------------------------------

build_arg(Bs) ->
    build_arg(Bs, 0).

build_arg([B|Bs], N) ->
    build_arg(Bs, (N bsl 8) bor B);
build_arg([], N) ->
    N.

%%-----------------------------------------------------------------------
%% Decodes a bunch of arguments and returns them in a list
%%-----------------------------------------------------------------------

decode_n_args(N, Bs, Atoms, Literals) when N >= 0 ->
    decode_n_args(N, [], Bs, Atoms, Literals).

decode_n_args(N, Acc, Bs0, Atoms, Literals) when N > 0 ->
    {A1,Bs} = decode_arg(Bs0, Atoms, Literals),
    decode_n_args(N-1, [A1|Acc], Bs, Atoms, Literals);
decode_n_args(0, Acc, Bs, _, _) ->
    {lists:reverse(Acc),Bs}.

%%-----------------------------------------------------------------------
%% Convert a numeric tag value into a symbolic one
%%-----------------------------------------------------------------------

-spec decode_tag(0..7) -> symbolic_tag().

decode_tag(?tag_u) -> u;
decode_tag(?tag_i) -> i;
decode_tag(?tag_a) -> a;
decode_tag(?tag_x) -> x;
decode_tag(?tag_y) -> y;
decode_tag(?tag_f) -> f;
decode_tag(?tag_h) -> h;
decode_tag(?tag_z) -> z.

%%-----------------------------------------------------------------------
%% - replace all references {a,I} with the atom with index I (or {atom,A})
%% - replace all references to {i,K} in an external call position with
%%    the proper MFA (position in list, first elt = 0, yields MFA to use)
%% - resolve strings, represented as <offset, length>, into their
%%   actual values by using string table
%%    (note: string table should be passed as a BINARY so that we can
%%    use binary_to_list/3!)
%% - convert instruction to its readable form ...
%% 
%% Currently, only the first three are done (systematically, at least).
%%
%% Note: It MAY be premature to remove the lists of args, since that
%%  representation means it is simpler to iterate over all args, etc.
%%-----------------------------------------------------------------------

resolve_names(Fun, Imports, Str, Lbls, Lambdas, Literals, M) ->
    [resolve_inst(Instr, Imports, Str, Lbls, Lambdas, Literals, M) || Instr <- Fun].

%%
%% New make_fun2/4 instruction added in August 2001 (R8).
%% We handle it specially here to avoid adding an argument to
%% the clause for every instruction.
%%

resolve_inst({make_fun2,Args}, _, _, _, Lambdas, _, M) ->
    [OldIndex] = resolve_args(Args),
    {OldIndex,{F,A,_Lbl,_Index,NumFree,OldUniq}} =
	lists:keyfind(OldIndex, 1, Lambdas),
    {make_fun2,{M,F,A},OldIndex,OldUniq,NumFree};
resolve_inst(Instr, Imports, Str, Lbls, _Lambdas, _Literals, _M) ->
    %% io:format(?MODULE_STRING":resolve_inst ~p.~n", [Instr]),
    resolve_inst(Instr, Imports, Str, Lbls).

resolve_inst({label,[{u,L}]},_,_,_) ->
    {label,L};
resolve_inst(FuncInfo,_,_,_) when element(1, FuncInfo) =:= func_info -> 
    FuncInfo; % already resolved
%% resolve_inst(int_code_end,_,_,_,_) ->  % instruction already handled
%%    int_code_end;                       % should not really be handled here
resolve_inst({call,[{u,N},{f,L}]},_,_,Lbls) ->
    {call,N,lookup(L,Lbls)};
resolve_inst({call_last,[{u,N},{f,L},{u,U}]},_,_,Lbls) ->
    {call_last,N,lookup(L,Lbls),U};
resolve_inst({call_only,[{u,N},{f,L}]},_,_,Lbls) ->
    {call_only,N,lookup(L,Lbls)};
resolve_inst({call_ext,[{u,N},{u,MFAix}]},Imports,_,_) ->
    {call_ext,N,lookup(MFAix+1,Imports)};
resolve_inst({call_ext_last,[{u,N},{u,MFAix},{u,X}]},Imports,_,_) ->
    {call_ext_last,N,lookup(MFAix+1,Imports),X};
resolve_inst({bif0,Args},Imports,_,_) ->
    [Bif,Reg] = resolve_args(Args),
    {extfunc,_Mod,BifName,_Arity} = lookup(Bif+1,Imports),
    {bif,BifName,nofail,[],Reg};
resolve_inst({bif1,Args},Imports,_,_) ->
    [F,Bif,A1,Reg] = resolve_args(Args),
    {extfunc,_Mod,BifName,_Arity} = lookup(Bif+1,Imports),
    {bif,BifName,F,[A1],Reg};
resolve_inst({bif2,Args},Imports,_,_) ->
    [F,Bif,A1,A2,Reg] = resolve_args(Args),
    {extfunc,_Mod,BifName,_Arity} = lookup(Bif+1,Imports),
    {bif,BifName,F,[A1,A2],Reg};
resolve_inst({allocate,[{u,X0},{u,X1}]},_,_,_) ->
    {allocate,X0,X1};
resolve_inst({allocate_heap,[{u,X0},{u,X1},{u,X2}]},_,_,_) ->
    {allocate_heap,X0,X1,X2};
resolve_inst({allocate_zero,[{u,X0},{u,X1}]},_,_,_) ->
    {allocate_zero,X0,X1};
resolve_inst({allocate_heap_zero,[{u,X0},{u,X1},{u,X2}]},_,_,_) ->
    {allocate_heap_zero,X0,X1,X2};
resolve_inst({test_heap,[{u,X0},{u,X1}]},_,_,_) ->
    {test_heap,X0,X1};
resolve_inst({init,[Dst]},_,_,_) ->
    {init,Dst};
resolve_inst({deallocate,[{u,L}]},_,_,_) ->
    {deallocate,L};
resolve_inst({return,[]},_,_,_) ->
    return;
resolve_inst({send,[]},_,_,_) ->
    send;
resolve_inst({remove_message,[]},_,_,_) ->
    remove_message;
resolve_inst({timeout,[]},_,_,_) ->
    timeout;
resolve_inst({loop_rec,[Lbl,Dst]},_,_,_) ->
    {loop_rec,Lbl,Dst};
resolve_inst({loop_rec_end,[Lbl]},_,_,_) ->
    {loop_rec_end,Lbl};
resolve_inst({wait,[Lbl]},_,_,_) ->
    {wait,Lbl};
resolve_inst({wait_timeout,[Lbl,Int]},_,_,_) ->
    {wait_timeout,Lbl,resolve_arg(Int)};
resolve_inst({m_plus,Args},_,_,_) ->
    [W,SrcR1,SrcR2,DstR] = resolve_args(Args),
    {arithbif,'+',W,[SrcR1,SrcR2],DstR};
resolve_inst({m_minus,Args},_,_,_) ->
    [W,SrcR1,SrcR2,DstR] = resolve_args(Args),
    {arithbif,'-',W,[SrcR1,SrcR2],DstR};
resolve_inst({m_times,Args},_,_,_) ->
    [W,SrcR1,SrcR2,DstR] = resolve_args(Args),
    {arithbif,'*',W,[SrcR1,SrcR2],DstR};
resolve_inst({m_div,Args},_,_,_) ->
    [W,SrcR1,SrcR2,DstR] = resolve_args(Args),
    {arithbif,'/',W,[SrcR1,SrcR2],DstR};
resolve_inst({int_div,Args},_,_,_) ->
    [W,SrcR1,SrcR2,DstR] = resolve_args(Args),
    {arithbif,'div',W,[SrcR1,SrcR2],DstR};
resolve_inst({int_rem,Args},_,_,_) ->
    [W,SrcR1,SrcR2,DstR] = resolve_args(Args),
    {arithbif,'rem',W,[SrcR1,SrcR2],DstR};
resolve_inst({int_band,Args},_,_,_) ->
    [W,SrcR1,SrcR2,DstR] = resolve_args(Args),
    {arithbif,'band',W,[SrcR1,SrcR2],DstR};
resolve_inst({int_bor,Args},_,_,_) ->
    [W,SrcR1,SrcR2,DstR] = resolve_args(Args),
    {arithbif,'bor',W,[SrcR1,SrcR2],DstR};
resolve_inst({int_bxor,Args},_,_,_) ->
    [W,SrcR1,SrcR2,DstR] = resolve_args(Args),
    {arithbif,'bxor',W,[SrcR1,SrcR2],DstR};
resolve_inst({int_bsl,Args},_,_,_) ->
    [W,SrcR1,SrcR2,DstR] = resolve_args(Args),
    {arithbif,'bsl',W,[SrcR1,SrcR2],DstR};
resolve_inst({int_bsr,Args},_,_,_) ->
    [W,SrcR1,SrcR2,DstR] = resolve_args(Args),
    {arithbif,'bsr',W,[SrcR1,SrcR2],DstR};
resolve_inst({int_bnot,Args},_,_,_) ->
    [W,SrcR,DstR] = resolve_args(Args),
    {arithbif,'bnot',W,[SrcR],DstR};
resolve_inst({is_lt=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_ge=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_eq=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_ne=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_eq_exact=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_ne_exact=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_integer=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_float=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_number=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_atom=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_pid=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_reference=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_port=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_nil=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_binary=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_constant=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_list=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_nonempty_list=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({is_tuple=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({test_arity=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({select_val,Args},_,_,_) ->
    [Reg,FLbl,{{z,1},{u,_Len},List0}] = Args,
    List = resolve_args(List0),
    {select_val,Reg,FLbl,{list,List}};
resolve_inst({select_tuple_arity,Args},_,_,_) ->
    [Reg,FLbl,{{z,1},{u,_Len},List0}] = Args,
    List = resolve_args(List0),
    {select_tuple_arity,Reg,FLbl,{list,List}};
resolve_inst({jump,[Lbl]},_,_,_) ->
    {jump,Lbl};
resolve_inst({'catch',[Dst,Lbl]},_,_,_) ->
    {'catch',Dst,Lbl};
resolve_inst({catch_end,[Dst]},_,_,_) ->
    {catch_end,Dst};
resolve_inst({move,[Src,Dst]},_,_,_) ->
    {move,resolve_arg(Src),Dst};
resolve_inst({get_list,[Src,Dst1,Dst2]},_,_,_) ->
    {get_list,Src,Dst1,Dst2};
resolve_inst({get_tuple_element,[Src,{u,Off},Dst]},_,_,_) ->
    {get_tuple_element,resolve_arg(Src),Off,resolve_arg(Dst)};
resolve_inst({set_tuple_element,[Src,Dst,{u,Off}]},_,_,_) ->
    {set_tuple_element,resolve_arg(Src),resolve_arg(Dst),Off};
resolve_inst({put_string,[{u,Len},{u,Off},Dst]},_,Strings,_) ->
    String = if Len > 0 -> binary_to_list(Strings, Off+1, Off+Len);
		true -> ""
	     end,
    {put_string,Len,{string,String},Dst};
resolve_inst({put_list,[Src1,Src2,Dst]},_,_,_) ->
    {put_list,resolve_arg(Src1),resolve_arg(Src2),Dst};
resolve_inst({put_tuple,[{u,Arity},Dst]},_,_,_) ->
    {put_tuple,Arity,Dst};
resolve_inst({put,[Src]},_,_,_) ->
    {put,resolve_arg(Src)};
resolve_inst({badmatch,[X]},_,_,_) ->
    {badmatch,resolve_arg(X)};
resolve_inst({if_end,[]},_,_,_) ->
    if_end;
resolve_inst({case_end,[X]},_,_,_) ->
    {case_end,resolve_arg(X)};
resolve_inst({call_fun,[{u,N}]},_,_,_) ->
    {call_fun,N};
resolve_inst({make_fun,Args},_,_,Lbls) ->
    [{f,L},Magic,FreeVars] = resolve_args(Args),
    {make_fun,lookup(L,Lbls),Magic,FreeVars};
resolve_inst({is_function=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};
resolve_inst({call_ext_only,[{u,N},{u,MFAix}]},Imports,_,_) ->
    {call_ext_only,N,lookup(MFAix+1,Imports)};
%%
%% Instructions for handling binaries added in R7A & R7B
%%
resolve_inst({bs_start_match,[F,Reg]},_,_,_) ->
    {bs_start_match,F,Reg};
resolve_inst({bs_get_integer=I,[Lbl,Arg2,{u,N},{u,U},Arg5]},_,_,_) ->
    [A2,A5] = resolve_args([Arg2,Arg5]),
    {test,I,Lbl,[A2,N,decode_field_flags(U),A5]};
resolve_inst({bs_get_float=I,[Lbl,Arg2,{u,N},{u,U},Arg5]},_,_,_) ->
    [A2,A5] = resolve_args([Arg2,Arg5]),
    {test,I,Lbl,[A2,N,decode_field_flags(U),A5]};
resolve_inst({bs_get_binary=I,[Lbl,Arg2,{u,N},{u,U},Arg5]},_,_,_) ->
    [A2,A5] = resolve_args([Arg2,Arg5]),
    {test,I,Lbl,[A2,N,decode_field_flags(U),A5]};
resolve_inst({bs_skip_bits,[Lbl,Arg2,{u,N},{u,U}]},_,_,_) ->
    A2 = resolve_arg(Arg2),
    {test,bs_skip_bits,Lbl,[A2,N,decode_field_flags(U)]};
resolve_inst({bs_test_tail,[F,{u,N}]},_,_,_) ->
    {test,bs_test_tail,F,[N]};
resolve_inst({bs_save,[{u,N}]},_,_,_) ->
    {bs_save,N};
resolve_inst({bs_restore,[{u,N}]},_,_,_) ->
    {bs_restore,N};
resolve_inst({bs_init,[{u,N},{u,U}]},_,_,_) ->
    {bs_init,N,decode_field_flags(U)};
resolve_inst({bs_final,[F,X]},_,_,_) ->
    {bs_final,F,X};
resolve_inst({bs_put_integer,[Lbl,Arg2,{u,N},{u,U},Arg5]},_,_,_) ->
    [A2,A5] = resolve_args([Arg2,Arg5]),
    {bs_put_integer,Lbl,A2,N,decode_field_flags(U),A5};
resolve_inst({bs_put_binary,[Lbl,Arg2,{u,N},{u,U},Arg5]},_,_,_) ->
    [A2,A5] = resolve_args([Arg2,Arg5]),
    {bs_put_binary,Lbl,A2,N,decode_field_flags(U),A5};
resolve_inst({bs_put_float,[Lbl,Arg2,{u,N},{u,U},Arg5]},_,_,_) ->
    [A2,A5] = resolve_args([Arg2,Arg5]),
    {bs_put_float,Lbl,A2,N,decode_field_flags(U),A5};
resolve_inst({bs_put_string,[{u,Len},{u,Off}]},_,Strings,_) ->
    String = if Len > 0 -> binary_to_list(Strings, Off+1, Off+Len);
		true -> ""
	     end,
    {bs_put_string,Len,{string,String}};
resolve_inst({bs_need_buf,[{u,N}]},_,_,_) ->
    {bs_need_buf,N};

%%
%% Instructions for handling floating point numbers added in June 2001 (R8).
%%
resolve_inst({fclearerror,[]},_,_,_) ->
    fclearerror;
resolve_inst({fcheckerror,[Arg]},_,_,_) ->
    {fcheckerror,resolve_arg(Arg)};
resolve_inst({fmove,Args},_,_,_) ->
    [FR,Reg] = resolve_args(Args),
    {fmove,FR,Reg};
resolve_inst({fconv,Args},_,_,_) ->
    [Reg,FR] = resolve_args(Args),
    {fconv,Reg,FR};
resolve_inst({fadd=I,Args},_,_,_) ->
    [F,A1,A2,Reg] = resolve_args(Args),
    {arithfbif,I,F,[A1,A2],Reg};
resolve_inst({fsub=I,Args},_,_,_) ->
    [F,A1,A2,Reg] = resolve_args(Args),
    {arithfbif,I,F,[A1,A2],Reg};
resolve_inst({fmul=I,Args},_,_,_) ->
    [F,A1,A2,Reg] = resolve_args(Args),
    {arithfbif,I,F,[A1,A2],Reg};
resolve_inst({fdiv=I,Args},_,_,_) ->
    [F,A1,A2,Reg] = resolve_args(Args),
    {arithfbif,I,F,[A1,A2],Reg};
resolve_inst({fnegate,Args},_,_,_) ->
    [F,Arg,Reg] = resolve_args(Args),
    {arithfbif,fnegate,F,[Arg],Reg};

%%
%% Instructions for try expressions added in January 2003 (R10).
%%
resolve_inst({'try',[Reg,Lbl]},_,_,_) -> % analogous to 'catch'
    {'try',Reg,Lbl};
resolve_inst({try_end,[Reg]},_,_,_) ->   % analogous to 'catch_end'
    {try_end,Reg};
resolve_inst({try_case,[Reg]},_,_,_) ->  % analogous to 'catch_end'
    {try_case,Reg};
resolve_inst({try_case_end,[Arg]},_,_,_) ->
    {try_case_end,resolve_arg(Arg)};
resolve_inst({raise,[_Reg1,_Reg2]=Regs},_,_,_) ->
    {raise,{f,0},Regs,{x,0}};		 % do NOT wrap this as a 'bif'
					 % as there is no raise/2 bif!

%%
%% New bit syntax instructions added in February 2004 (R10B).
%%
resolve_inst({bs_init2,[Lbl,Arg2,{u,W},{u,R},{u,F},Arg6]},_,_,_) ->
    [A2,A6] = resolve_args([Arg2,Arg6]),
    {bs_init2,Lbl,A2,W,R,decode_field_flags(F),A6};
resolve_inst({bs_bits_to_bytes,[Lbl,Arg2,Arg3]},_,_,_) ->
    [A2,A3] = resolve_args([Arg2,Arg3]),
    {bs_bits_to_bytes,Lbl,A2,A3};
resolve_inst({bs_add=I,[Lbl,Arg2,Arg3,Arg4,Arg5]},_,_,_) ->
    [A2,A3,A4,A5] = resolve_args([Arg2,Arg3,Arg4,Arg5]),
    {I,Lbl,[A2,A3,A4],A5};

%%
%% New apply instructions added in April 2004 (R10B).
%%
resolve_inst({apply,[{u,Arity}]},_,_,_) ->
    {apply,Arity};
resolve_inst({apply_last,[{u,Arity},{u,D}]},_,_,_) ->
    {apply_last,Arity,D};

%%
%% New test instruction added in April 2004 (R10B).
%%
resolve_inst({is_boolean=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};

%%
%% New instruction added in June 2005.
%%
resolve_inst({is_function2=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};

%%
%% New bit syntax matching added in Dec 2005 (R11B).
%%
resolve_inst({bs_start_match2=I,[F,Reg,{u,Live},{u,Max},Ms]},_,_,_) ->
    {test,I,F,[Reg,Live,Max,Ms]};
resolve_inst({bs_get_integer2=I,[Lbl,Ms,{u,Live},Arg2,{u,N},{u,U},Arg5]},_,_,_) ->
    [A2,A5] = resolve_args([Arg2,Arg5]),
    {test,I,Lbl,[Ms, Live,A2,N,decode_field_flags(U),A5]};
resolve_inst({bs_get_binary2=I,[Lbl,Ms,{u,Live},Arg2,{u,N},{u,U},Arg5]},_,_,_) ->
    [A2,A5] = resolve_args([Arg2,Arg5]),
    {test,I,Lbl,[Ms, Live,A2,N,decode_field_flags(U),A5]};
resolve_inst({bs_get_float2=I,[Lbl,Ms,{u,Live},Arg2,{u,N},{u,U},Arg5]},_,_,_) ->
    [A2,A5] = resolve_args([Arg2,Arg5]),
    {test,I,Lbl,[Ms, Live,A2,N,decode_field_flags(U),A5]};
resolve_inst({bs_skip_bits2=I,[Lbl,Ms,Arg2,{u,N},{u,U}]},_,_,_) ->
    A2 = resolve_arg(Arg2),
    {test,I,Lbl,[Ms,A2,N,decode_field_flags(U)]};
resolve_inst({bs_test_tail2=I,[F,Ms,{u,N}]},_,_,_) ->
    {test,I,F,[Ms,N]};
resolve_inst({bs_save2=I,[Ms,{u,N}]},_,_,_) ->
    {I,Ms,N};
resolve_inst({bs_restore2=I,[Ms,{u,N}]},_,_,_) ->
    {I,Ms,N};
resolve_inst({bs_save2=I,[Ms,{atom,_}=Atom]},_,_,_) ->
    %% New operand type in R12B.
    {I,Ms,Atom};
resolve_inst({bs_restore2=I,[Ms,{atom,_}=Atom]},_,_,_) ->
    %% New operand type in R12B.
    {I,Ms,Atom};

%%
%% New instructions for guard BIFs that may GC. Added in Jan 2006 (R11B).
%%
resolve_inst({gc_bif1,Args},Imports,_,_) ->
    [F,Live,Bif,A1,Reg] = resolve_args(Args),
    {extfunc,_Mod,BifName,_Arity} = lookup(Bif+1,Imports),
    {gc_bif,BifName,F,Live,[A1],Reg};
resolve_inst({gc_bif2,Args},Imports,_,_) ->
    [F,Live,Bif,A1,A2,Reg] = resolve_args(Args),
    {extfunc,_Mod,BifName,_Arity} = lookup(Bif+1,Imports),
    {gc_bif,BifName,F,Live,[A1,A2],Reg};
%%
%% New instruction in R14, gc_bif with 3 arguments
%%
resolve_inst({gc_bif3,Args},Imports,_,_) ->
    [F,Live,Bif,A1,A2,A3,Reg] = resolve_args(Args),
    {extfunc,_Mod,BifName,_Arity} = lookup(Bif+1,Imports),
    {gc_bif,BifName,F,Live,[A1,A2,A3],Reg};

%%
%% New instructions for creating non-byte aligned binaries.
%%
resolve_inst({bs_final2,[X,Y]},_,_,_) ->
    {bs_final2,X,Y};

%%
%% R11B-5.
%% 
resolve_inst({is_bitstr=I,Args0},_,_,_) ->
    [L|Args] = resolve_args(Args0),
    {test,I,L,Args};

%%
%% R12B.
%%
resolve_inst({bs_context_to_binary=I,[Reg0]},_,_,_) ->
    Reg = resolve_arg(Reg0),
    {I,Reg};
resolve_inst({bs_test_unit=I,[F,Ms,{u,N}]},_,_,_) ->
    {test,I,F,[Ms,N]};
resolve_inst({bs_match_string=I,[F,Ms,{u,Bits},{u,Off}]},_,Strings,_) ->
    Len = (Bits+7) div 8,
    String = if
		 Len > 0 -> 
		     <<_:Off/binary,Bin:Len/binary,_/binary>> = Strings,
		     Bin;
		 true -> <<>>
	     end,
    {test,I,F,[Ms,Bits,String]};
resolve_inst({bs_init_writable=I,[]},_,_,_) ->
    I;
resolve_inst({bs_append=I,[Lbl,Arg2,{u,W},{u,R},{u,U},Arg6,{u,F},Arg8]},_,_,_) ->
    [A2,A6,A8] = resolve_args([Arg2,Arg6,Arg8]),
    {I,Lbl,A2,W,R,U,A6,decode_field_flags(F),A8};
resolve_inst({bs_private_append=I,[Lbl,Arg2,{u,U},Arg4,{u,F},Arg6]},_,_,_) ->
    [A2,A4,A6] = resolve_args([Arg2,Arg4,Arg6]),
    {I,Lbl,A2,U,A4,decode_field_flags(F),A6};
resolve_inst({trim=I,[{u,N},{u,Remaining}]},_,_,_) ->
    {I,N,Remaining};
resolve_inst({bs_init_bits,[Lbl,Arg2,{u,W},{u,R},{u,F},Arg6]},_,_,_) ->
    [A2,A6] = resolve_args([Arg2,Arg6]),
    {bs_init_bits,Lbl,A2,W,R,decode_field_flags(F),A6};

%%
%% R12B-5.
%%
resolve_inst({bs_get_utf8=I,[Lbl,Arg2,Arg3,{u,U},Arg4]},_,_,_) ->
    [A2,A3,A4] = resolve_args([Arg2,Arg3,Arg4]),
    {test,I,Lbl,[A2,A3,decode_field_flags(U),A4]};
resolve_inst({bs_skip_utf8=I,[Lbl,Arg2,Arg3,{u,U}]},_,_,_) ->
    [A2,A3] = resolve_args([Arg2,Arg3]),
    {test,I,Lbl,[A2,A3,decode_field_flags(U)]};
resolve_inst({bs_get_utf16=I,[Lbl,Arg2,Arg3,{u,U},Arg4]},_,_,_) ->
    [A2,A3,A4] = resolve_args([Arg2,Arg3,Arg4]),
    {test,I,Lbl,[A2,A3,decode_field_flags(U),A4]};
resolve_inst({bs_skip_utf16=I,[Lbl,Arg2,Arg3,{u,U}]},_,_,_) ->
    [A2,A3] = resolve_args([Arg2,Arg3]),
    {test,I,Lbl,[A2,A3,decode_field_flags(U)]};
resolve_inst({bs_get_utf32=I,[Lbl,Arg2,Arg3,{u,U},Arg4]},_,_,_) ->
    [A2,A3,A4] = resolve_args([Arg2,Arg3,Arg4]),
    {test,I,Lbl,[A2,A3,decode_field_flags(U),A4]};
resolve_inst({bs_skip_utf32=I,[Lbl,Arg2,Arg3,{u,U}]},_,_,_) ->
    [A2,A3] = resolve_args([Arg2,Arg3]),
    {test,I,Lbl,[A2,A3,decode_field_flags(U)]};
resolve_inst({bs_utf8_size=I,[Lbl,Arg2,Arg3]},_,_,_) ->
    [A2,A3] = resolve_args([Arg2,Arg3]),
    {I,Lbl,A2,A3};
resolve_inst({bs_put_utf8=I,[Lbl,{u,U},Arg3]},_,_,_) ->
    A3 = resolve_arg(Arg3),
    {I,Lbl,decode_field_flags(U),A3};
resolve_inst({bs_utf16_size=I,[Lbl,Arg2,Arg3]},_,_,_) ->
    [A2,A3] = resolve_args([Arg2,Arg3]),
    {I,Lbl,A2,A3};
resolve_inst({bs_put_utf16=I,[Lbl,{u,U},Arg3]},_,_,_) ->
    A3 = resolve_arg(Arg3),
    {I,Lbl,decode_field_flags(U),A3};
resolve_inst({bs_put_utf32=I,[Lbl,{u,U},Arg3]},_,_,_) ->
    A3 = resolve_arg(Arg3),
    {I,Lbl,decode_field_flags(U),A3};

%%
%% R13B03.
%%
resolve_inst({on_load,[]},_,_,_) ->
    on_load;

%%
%% R14A.
%%
resolve_inst({recv_mark,[Lbl]},_,_,_) ->
    {recv_mark,Lbl};
resolve_inst({recv_set,[Lbl]},_,_,_) ->
    {recv_set,Lbl};

%%
%% Catches instructions that are not yet handled.
%%
resolve_inst(X,_,_,_) -> ?exit({resolve_inst,X}).

%%-----------------------------------------------------------------------
%% Resolves arguments in a generic way.
%%-----------------------------------------------------------------------

resolve_args(Args) -> [resolve_arg(A) || A <- Args].

resolve_arg({x,N} = Arg) when is_integer(N), N >= 0 -> Arg;
resolve_arg({y,N} = Arg) when is_integer(N), N >= 0 -> Arg;
resolve_arg({fr,N} = Arg) when is_integer(N), N >= 0 -> Arg;
resolve_arg({f,N} = Arg) when is_integer(N), N >= 0 -> Arg;
resolve_arg({u,_} = Arg) -> resolve_arg_unsigned(Arg);
resolve_arg({i,_} = Arg) -> resolve_arg_integer(Arg);
resolve_arg({atom,Atom} = Arg) when is_atom(Atom) -> Arg;
resolve_arg({float,F} = Arg) when is_float(F) -> Arg;
resolve_arg({literal,_} = Arg) -> Arg;
resolve_arg(nil) -> nil.

resolve_arg_unsigned({u,N}) when is_integer(N), N >= 0 -> N.

resolve_arg_integer({i,N}) when is_integer(N) -> {integer,N}.

%%-----------------------------------------------------------------------
%% The purpose of the following is just to add a hook for future changes.
%% Currently, field flags are numbers 1-2-4-8 and only two of these
%% numbers (BSF_LITTLE 2 -- BSF_SIGNED 4) have a semantic significance;
%% others are just hints for speeding up the execution; see "erl_bits.h".
%%-----------------------------------------------------------------------

decode_field_flags(FF) ->
    {field_flags,FF}.

%%-----------------------------------------------------------------------
%% Private Utilities
%%-----------------------------------------------------------------------

mk_imports(ImportList) ->
    gb_trees:from_orddict([{I,{extfunc,M,F,A}} || {I,M,F,A} <- ImportList]).

mk_atoms(AtomList) ->
    gb_trees:from_orddict(AtomList).

mk_labels(LabelList) ->
    gb_trees:from_orddict(LabelList).

lookup(I, Imports) ->
    gb_trees:get(I, Imports).