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authorBjörn Gustavsson <[email protected]>2018-09-28 05:57:47 +0200
committerBjörn Gustavsson <[email protected]>2018-09-28 10:47:56 +0200
commit0bb261b730eff06cca524ea9999ff035585ef5b4 (patch)
treee057e70bc7fe53a7ec74577dfdb836707e7ae60b /lib/compiler/src
parent377f19f25aeec6939a6728bd0c4910086c22ccdc (diff)
downloadotp-0bb261b730eff06cca524ea9999ff035585ef5b4.tar.gz
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Fix rare bug in binary matching (again)
2e40d8d1c51a attempted fix a bug in binary matching, but it only fixed the bug for the minimized test case. This commit removes the previous fix and fixes the bug in a more effective way. See the comments in the new code in `sys_core_bsm` for an explanation. This commit restores the optimizations in string.erl and dets_v9.erl that the previous fix disabled. I have not found any code where this commit will disable optimizations when they are actually safe. There are some changes to the code in ssl_cipher.erl in that some bs_start_match2 instruction did not reuse the binary register for the match context, but the delayed sub binary optimizations was never applied to the code in the first place. https://bugs.erlang.org/browse/ERL-689
Diffstat (limited to 'lib/compiler/src')
-rw-r--r--lib/compiler/src/beam_bsm.erl13
-rw-r--r--lib/compiler/src/sys_core_bsm.erl62
2 files changed, 63 insertions, 12 deletions
diff --git a/lib/compiler/src/beam_bsm.erl b/lib/compiler/src/beam_bsm.erl
index abc6e96c85..1c8e0e9854 100644
--- a/lib/compiler/src/beam_bsm.erl
+++ b/lib/compiler/src/beam_bsm.erl
@@ -310,18 +310,7 @@ btb_reaches_match_2([{test,bs_start_match2,{f,F},Live,[Bin,_],Ctx}|Is],
end;
btb_reaches_match_2([{test,_,{f,F},Ss}=I|Is], Regs, D0) ->
btb_ensure_not_used(Ss, I, Regs),
- D1 = btb_follow_branch(F, Regs, D0),
- D = case Is of
- [{bs_context_to_binary,_}|_] ->
- %% bs_context_to_binary following a test instruction
- %% probably needs the current position to be saved as
- %% the new start position, but we can't be sure.
- %% Therefore, conservatively disable the optimization
- %% (instead of forcing a saving of the position).
- D1#btb{must_save=true,must_not_save=true};
- _ ->
- D1
- end,
+ D = btb_follow_branch(F, Regs, D0),
btb_reaches_match_1(Is, Regs, D);
btb_reaches_match_2([{test,_,{f,F},_,Ss,_}=I|Is], Regs, D0) ->
btb_ensure_not_used(Ss, I, Regs),
diff --git a/lib/compiler/src/sys_core_bsm.erl b/lib/compiler/src/sys_core_bsm.erl
index d7b26c3a56..62657933ee 100644
--- a/lib/compiler/src/sys_core_bsm.erl
+++ b/lib/compiler/src/sys_core_bsm.erl
@@ -44,6 +44,14 @@ function([{#c_var{name={F,Arity}}=Name,B0}|Fs], FsAcc, Ws0) ->
{B,Ws} ->
function(Fs, [{Name,B}|FsAcc], Ws)
catch
+ throw:unsafe_bs_context_to_binary ->
+ %% Unsafe bs_context_to_binary (in the sense that the
+ %% contents of the binary will probably be wrong).
+ %% Disable binary optimizations for the entire function.
+ %% We don't generate an INFO message, because this happens
+ %% very infrequently and it would be hard to explain in
+ %% a comprehensible way in an INFO message.
+ function(Fs, [{Name,B0}|FsAcc], Ws0);
Class:Error:Stack ->
io:fwrite("Function: ~w/~w\n", [F,Arity]),
erlang:raise(Class, Error, Stack)
@@ -116,12 +124,66 @@ move_from_col(Pos, L) ->
[Col|First] ++ Rest.
bsm_do_an([#c_var{name=Vname}=V0|Vs0], Cs0, Case) ->
+ bsm_inner_context_to_binary(Cs0),
Cs = bsm_do_an_var(Vname, Cs0),
V = bsm_annotate_for_reuse(V0),
Vs = core_lib:make_values([V|Vs0]),
Case#c_case{arg=Vs,clauses=Cs};
bsm_do_an(_Vs, _Cs, Case) -> Case.
+bsm_inner_context_to_binary([#c_clause{body=B}|Cs]) ->
+ %% Consider:
+ %%
+ %% foo(<<Length, Data/binary>>) -> %Line 1
+ %% case {Data, Length} of %Line 2
+ %% {_, 0} -> Data; %Line 3
+ %% {<<...>>, 4} -> ... %Line 4
+ %% end.
+ %%
+ %% No sub binary will be created for Data in line 1. The match
+ %% context will be passed on to the `case` in line 2. In line 3,
+ %% this pass inserts a `bs_context_to_binary` instruction to
+ %% convert the match context representing Data to a binary before
+ %% returning it. The problem is that the binary created will be
+ %% the original binary (including the matched out Length field),
+ %% not the tail of the binary as it is supposed to be.
+ %%
+ %% Here follows a heuristic to disable the binary optimizations
+ %% for the entire function if this code kind of code is found.
+
+ case cerl_trees:free_variables(B) of
+ [] ->
+ %% Since there are no free variables in the body of
+ %% this clause, there can't be any troublesome
+ %% bs_context_to_binary instructions.
+ bsm_inner_context_to_binary(Cs);
+ [_|_]=Free ->
+ %% One of the free variables could refer to a match context
+ %% created by the outer binary match.
+ F = fun(#c_primop{name=#c_literal{val=bs_context_to_binary},
+ args=[#c_var{name=V}]}, _) ->
+ case member(V, Free) of
+ true ->
+ %% This bs_context_to_binary instruction will
+ %% make a binary of the match context from an
+ %% outer binary match. It is very likely that
+ %% the contents of the binary will be wrong
+ %% (the original binary as opposed to only
+ %% the tail binary).
+ throw(unsafe_bs_context_to_binary);
+ false ->
+ %% Safe. This bs_context_to_binary instruction
+ %% will make a binary from a match context
+ %% defined in the body of the clause.
+ ok
+ end;
+ (_, _) ->
+ ok
+ end,
+ cerl_trees:fold(F, ok, B)
+ end;
+bsm_inner_context_to_binary([]) -> ok.
+
bsm_do_an_var(V, [#c_clause{pats=[P|_],guard=G,body=B0}=C0|Cs]) ->
case P of
#c_var{name=VarName} ->