* [musl] [PATCH] use __getauxval in mallocng
@ 2022-08-15 18:21 Érico Nogueira
2022-08-15 18:31 ` Rich Felker
0 siblings, 1 reply; 3+ messages in thread
From: Érico Nogueira @ 2022-08-15 18:21 UTC (permalink / raw)
To: musl; +Cc: Érico Nogueira
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [musl] [PATCH] use __getauxval in mallocng
2022-08-15 18:21 [musl] [PATCH] use __getauxval in mallocng Érico Nogueira
@ 2022-08-15 18:31 ` Rich Felker
2022-08-15 19:01 ` Érico Nogueira
0 siblings, 1 reply; 3+ messages in thread
From: Rich Felker @ 2022-08-15 18:31 UTC (permalink / raw)
To: Érico Nogueira; +Cc: musl
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [musl] [PATCH] use __getauxval in mallocng
2022-08-15 18:31 ` Rich Felker
@ 2022-08-15 19:01 ` Érico Nogueira
0 siblings, 0 replies; 3+ messages in thread
From: Érico Nogueira @ 2022-08-15 19:01 UTC (permalink / raw)
To: musl
On Mon Aug 15, 2022 at 3:31 PM -03, Rich Felker wrote:
> 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?
That does seem to be the case :/
From some quick testing, a program calling only malloc and freeing it
got ~60 bytes bigger.
I don't think there's a good way to get the best outcome in both
situations, is there? And 20 bytes in a shared mapping makes more sense.
>
> Rich
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2022-08-15 19:02 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-08-15 18:21 [musl] [PATCH] use __getauxval in mallocng Érico Nogueira
2022-08-15 18:31 ` Rich Felker
2022-08-15 19:01 ` Érico Nogueira
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/musl/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).