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Replace trailing 1-element arrays with C99 flex-arrays #3785

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Replace trailing 1-element arrays with C99 flex-arrays #3785

wants to merge 1 commit into from

Commits on Oct 7, 2023

  1. Replace trailing 1-element arrays with C99 flex-arrays 

    Using a trailing 1-element array as a variable-length array is undefined
behavior.  Compilers have traditionally allowed this, as this is a
traditional, pre-C99 convention.  But it's being increasingly phased out
in favor of C99 flexible arrays, which avoid ambiguity about whether the
array is intended to be variable-length or not.  gcc 13+ and clang 16+
support the -fstrict-flex-arrays=3 option, which Linux v6.5+ enables
globally, resulting in UBSAN errors when these arrays are accessed.
(See https://lore.kernel.org/r/00000000000049964e06041f2cbf@google.com)

Fix this by making zstd use C99 flexible arrays instead of 1-element
arrays.  This only affects three places (that I could find): one in
fse_decompress.c and two in zstdmt_compress.c.

Note, this breaks the c89build CI job and thus might not be suitable for
merging yet.  I recommend that zstd drop support for C89/C90.
    @ebiggers
    ebiggers committed Oct 7, 2023
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