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Fix a binary corruption bug occurring with private_append #2004

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Merged
merged 1 commit into from
Nov 27, 2025
Merged

Fix a binary corruption bug occurring with private_append #2004

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2 changes: 1 addition & 1 deletion src/libAtomVM/term.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1093,7 +1093,7 @@ term term_reuse_binary(term src, size_t size, Heap *heap, GlobalContext *glb)
}
// Not a refc binary or it's a const refc binary - create a new one
size_t src_size = term_binary_size(src);
term t = term_create_uninitialized_binary(size, heap, glb);
term t = term_create_empty_binary(size, heap, glb);
// Copy the source data (up to the smaller of src_size and size)
size_t copy_size = src_size < size ? src_size : size;
memcpy((void *) term_binary_data(t), (void *) term_binary_data(src), copy_size);
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21 changes: 21 additions & 0 deletions tests/erlang_tests/test_bs.erl
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Expand Up @@ -63,6 +63,10 @@ start() ->

<<1, 2, 3>> = test_bs_private_append(<<1, 2, 3>>),

% Large case sufficient to trigger a valgrind error if reused binary is not zero'd
Expected = make_binary_copy(32, 0, <<>>),
Expected = test_bs_private_append2(id(make_binary_copy(32, 240, <<>>)), <<>>),

nope = test_match_clause(<<"">>),
nope = test_match_clause(<<16#FF>>),
nope = test_match_clause(<<$n:8>>),
Expand Down Expand Up @@ -378,6 +382,18 @@ test_bs_append(Bin1, Bin2) ->
test_bs_private_append(Bin) ->
<<<<Byte:8>> || <<Byte:8>> <= Bin>>.

% This encodes with private_append and ensures we do this with buffers allocated on the heap
test_bs_private_append2(<<C1:8, C2:8, C3:8, C4:8, Rest/binary>>, Acc) when byte_size(Acc) < 16 ->
test_bs_private_append2(
Rest,
<<Acc/binary, C1:4, C2:4, C3:4, C4:4, C1:4, C2:4, C3:4, C4:4, C1:4, C2:4, C3:4, C4:4, C1:4,
C2:4, C3:4, C4:4, C1:4, C2:4, C3:4, C4:4>>
);
test_bs_private_append2(<<C1:8, C2:8, Rest/binary>>, Acc) ->
test_bs_private_append2(Rest, <<Acc/binary, C1:4, C2:4>>);
test_bs_private_append2(<<>>, Acc) ->
Acc.

test_match_clause(
<<$n:8, FixedBinaryData:4/binary, Rest/binary>>
) ->
Expand Down Expand Up @@ -410,6 +426,11 @@ make_binary(Size, Accum) ->
Byte = Size rem 256,
make_binary(Size - 1, <<Accum/binary, Byte:8>>).

make_binary_copy(0, _Byte, Acc) ->
Acc;
make_binary_copy(Count, Byte, Acc) ->
make_binary_copy(Count - 1, Byte, <<Byte, Acc/binary>>).

test_put_match_string(Prefix, Suffix) ->
Bin = <<$f:8, $o:8, $o:8, Suffix/binary>>,
<<Prefix:3/binary, $b:8, $a:8, $r:8>> = Bin.
Expand Down
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