Re: [musl] [PATCH v4] implement recallocarray(3)

[Rich Felker <dalias@libc.org>]

On Sun, Aug 02, 2020 at 04:54:26PM -0600, Ariadne Conill wrote:
> This OpenBSD extension is similar to reallocarray(3), but
> zero-initializes the new memory area.
> 
> This extension is placed in _BSD_SOURCE, like
> reallocarray(3).
> 
> Changes from v3:
> - use calloc() instead of realloc() and always copy
> - explicitly zero old memory block
> - restore overflow checking for old size
> 
> Changes from v2:
> - drop overflow checking for old size
> 
> Changes from v1:
> - use realloc() instead of reallocarray()

Can we finish discussion of questions raised before making new
versions with changes that haven't even been agreed upon? I asked
about EINVAL so we could determine if it's expected and if it's
reasonable to copy; that's not a demand to remove it. And the new
memset before free is a complete no-op. If there's a contract to
behave like explicit_bzero on the old memory, we may want to honor
that if we implement recallocarray, but that likely makes it entirely
unsuitable to the purpose you want it for and will bring back the
atrociously bad apk performance you previously saw with mallocng if
you use it there, since each increment of array size will incur a
whole memcpy of the existing array (quadratic time) rather than copies
only occuring a logarithmic number of times (yielding O(n log n)
overall) as would happen with realloc.

Overall I'm getting kinda skeptical of this function. Implementing it
without the hardness guarantees of the OpenBSD version seems like a
bad idea, but with those guarantees it just seems to be a bad
interface.

Rich