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avoid corrupting String on conversion of StringVector to String #39726

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Merged
vtjnash merged 1 commit into from
Feb 18, 2021
Merged

avoid corrupting String on conversion of StringVector to String #39726

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6 changes: 6 additions & 0 deletions src/array.c
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Original file line number Diff line number Diff line change
Expand Up @@ -483,6 +483,12 @@ JL_DLLEXPORT jl_array_t *jl_pchar_to_array(const char *str, size_t len)
JL_DLLEXPORT jl_value_t *jl_array_to_string(jl_array_t *a)
{
size_t len = jl_array_len(a);
if (len == 0) {
// this may seem like purely an optimization (which it also is), but it
// also ensures that calling `String(a)` doesn't corrupt a previous
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@quinnj quinnj Feb 18, 2021

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Just curious, but why/how exactly does a previous string get corrupted w/o this? The segfault seems to be gc-related; something about the original string now being "shared" between two strings?

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@vtjnash vtjnash Feb 18, 2021

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We truncate the array here (so that future uses will get a fresh data object), but that ends up truncating the string later, if it is still the data pointer and we call this immediately. See the added tests.

// string also created the same way, where `a = StringVector(_)`.
return jl_an_empty_string;
}
if (a->flags.how == 3 && a->offset == 0 && a->elsize == 1 &&
(jl_array_ndims(a) != 1 ||
((a->maxsize + sizeof(void*) + 1 <= GC_MAX_SZCLASS) == (len + sizeof(void*) + 1 <= GC_MAX_SZCLASS)))) {
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10 changes: 10 additions & 0 deletions test/core.jl
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Expand Up @@ -5299,6 +5299,16 @@ if Sys.WORD_SIZE == 64
@test_nowarn tester20360()
end

# issue #39717
let a = Base.StringVector(2^17)
b = String(a)
c = String(a)
GC.gc()
@test sizeof(a) == 0
@test sizeof(b) == 2^17
@test sizeof(c) == 0
end

@test_throws ArgumentError eltype(Bottom)

# issue #16424, re-evaluating type definitions
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