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Message-ID: <vwm7ovyywiewuypt7d6lk6e4tdxtjsc4koswdtevfwgac5o3zy@7z2tcbrg3uja>
Date: Fri, 31 Oct 2025 00:29:25 +0100
From: Alejandro Colomar <alx@...nel.org>
To: libc-alpha@...rceware.org, musl@...ts.openwall.com
Cc: Arthur O'Dwyer <arthur.j.odwyer@...il.com>,
Jonathan Wakely <jwakely@...hat.com>, Thiago Macieira <thiago@...ieira.org>
Subject: alignment guarantees from realloc(3)
Hi!
A discussion in the C++ std-proposals@ mailing list triggered a
discussion about the lack of aligned_realloc().
I don't think we want an aligned_realloc(), as it would be very weird to
change the alignment of a block of memory. Once you have there some
contents, the alignment would just have to be preserved.
Thus, I think realloc(3) should preserve the alignment from a previous
aligned_alloc(3), and thus, not need an aligned_realloc() at all.
Before writing a proposal for the standards, I'd like to ask about the
feasibility of adding this guarantee in realloc(3) in glibc and musl.
Would you mind adding such a guarantee to realloc(3)?
The precise wording I'm considering for a standards proposal will look
something like this:
realloc(3) shall preserve the alignment of a block allocated
previously by aligned_alloc(3).
Have a lovely night!
Alex
--
<https://www.alejandro-colomar.es>
Use port 80 (that is, <...:80/>).
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