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Message-ID: <6718676e-9067-6a46-d25f-80c508e3976a@samersoff.net>
Date: Sun, 2 Aug 2020 11:07:16 +0300
From: Dmitry Samersoff <dms@...ersoff.net>
To: musl@...ts.openwall.com, Ariadne Conill <ariadne@...eferenced.org>
Subject: Re: [PATCH v3] implement recallocarray(3)
Ariadne,
BSD (jemalloc) realloc always perform a new allocation and may return
completely new pointer ever if new_size <= old_size.
Also contract for realloc says that if allocation fails original content
should remain untouched.
I don't know how musl malloc perform in this case, but it might be
better to move all memset after realloc and use newptr as a memeset
base, with an appropriate error checking.
-Dmitry
On 02.08.2020 0:42, 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 v2:
> - drop overflow checking for old size
>
> Changes from v1:
> - use realloc() instead of reallocarray()
> ---
> include/stdlib.h | 1 +
> src/malloc/recallocarray.c | 27 +++++++++++++++++++++++++++
> 2 files changed, 28 insertions(+)
> create mode 100644 src/malloc/recallocarray.c
>
> diff --git a/include/stdlib.h b/include/stdlib.h
> index b54a051f..a0412ad4 100644
> --- a/include/stdlib.h
> +++ b/include/stdlib.h
> @@ -146,6 +146,7 @@ int clearenv(void);
> #define WCOREDUMP(s) ((s) & 0x80)
> #define WIFCONTINUED(s) ((s) == 0xffff)
> void *reallocarray (void *, size_t, size_t);
> +void *recallocarray (void *, size_t, size_t, size_t);
> #endif
>
> #ifdef _GNU_SOURCE
> diff --git a/src/malloc/recallocarray.c b/src/malloc/recallocarray.c
> new file mode 100644
> index 00000000..a7827604
> --- /dev/null
> +++ b/src/malloc/recallocarray.c
> @@ -0,0 +1,27 @@
> +#define _BSD_SOURCE
> +#include <errno.h>
> +#include <stdlib.h>
> +#include <string.h>
> +
> +void *recallocarray(void *ptr, size_t om, size_t m, size_t n)
> +{
> + void *newptr;
> + size_t old_size = om * n, new_size;
> +
> + if (n && m > -1 / n) {
> + errno = ENOMEM;
> + return 0;
> + }
> + new_size = m * n;
> +
> + if (new_size <= old_size) {
> + memset((char *) ptr + new_size, 0, old_size - new_size);
> + }
> +
> + newptr = realloc(ptr, m * n);
> + if (new_size > old_size) {
> + memset((char *) ptr + old_size, 0, new_size - old_size);
> + }
> +
> + return newptr;
> +}
>
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