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Date: Mon, 15 Aug 2022 14:31:15 -0400
From: Rich Felker <dalias@...c.org>
To: Érico Nogueira <ericonr@...root.org>
Cc: musl@...ts.openwall.com
Subject: Re: [PATCH] use __getauxval in mallocng
On Mon, Aug 15, 2022 at 03:21:10PM -0300, Érico Nogueira wrote:
> saves around 20 bytes of .text
> ---
> src/malloc/mallocng/glue.h | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/src/malloc/mallocng/glue.h b/src/malloc/mallocng/glue.h
> index 151c48b8..4b988fb2 100644
> --- a/src/malloc/mallocng/glue.h
> +++ b/src/malloc/mallocng/glue.h
> @@ -12,6 +12,7 @@
> #include "libc.h"
> #include "lock.h"
> #include "dynlink.h"
> +#include "sys/auxv.h"
>
> // use macros to appropriately namespace these.
> #define size_classes __malloc_size_classes
> @@ -42,9 +43,8 @@
> static inline uint64_t get_random_secret()
> {
> uint64_t secret = (uintptr_t)&secret * 1103515245;
> - for (size_t i=0; libc.auxv[i]; i+=2)
> - if (libc.auxv[i]==AT_RANDOM)
> - memcpy(&secret, (char *)libc.auxv[i+1]+8, sizeof secret);
> + const char *at_random = (void *)__getauxval(AT_RANDOM);
> + if (at_random) memcpy(&secret, at_random+8, sizeof secret);
> return secret;
> }
>
> --
> 2.37.2
Hm, this might be worth doing. I'm trying to remember if there was a
reason it wasn't done initially. It wasn't absence of a namespace-safe
version because __getauxval already existed when mallocng was merged.
And it doesn't look like there's an early-use issue before getauxval
is usable either. Might it just be more expensive in the static linked
case where __getauxval isn't otherwise used?
Rich
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