From: Szabolcs Nagy <szabolcs.nagy@arm.com>
To: libc-alpha@sourceware.org, Richard.Earnshaw@arm.com,
DJ Delorie <dj@redhat.com>
Subject: [PATCH 08/16] malloc: Use global flag instead of function pointer dispatch for mtag
Date: Thu, 4 Mar 2021 16:32:27 +0000 [thread overview]
Message-ID: <8d9711a654bfe7a47ba743ab7e836118f8866f66.1614874816.git.szabolcs.nagy@arm.com> (raw)
In-Reply-To: <cover.1614874816.git.szabolcs.nagy@arm.com>
A flag check can be faster than function pointers because of how
branch prediction and speculation works and it can also remove a layer
of indirection when there is a mismatch between the malloc internal
tag_* api and __libc_mtag_* target hooks.
Memory tagging wrapper functions are moved to malloc.c from arena.c and
the logic now checks mmap_enabled. The definition of tag_new_usable is
moved after chunk related definitions.
This refactoring also allows using mtag_enabled checks instead of
USE_MTAG ifdefs when memory tagging support only changes code logic
when memory tagging is enabled at runtime.
---
malloc/arena.c | 33 +---------------------------
malloc/malloc.c | 58 ++++++++++++++++++++++++++++++++-----------------
2 files changed, 39 insertions(+), 52 deletions(-)
diff --git a/malloc/arena.c b/malloc/arena.c
index d0778fea92..1e83bb66bd 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -287,34 +287,6 @@ extern struct dl_open_hook *_dl_open_hook;
libc_hidden_proto (_dl_open_hook);
#endif
-#ifdef USE_MTAG
-
-/* Generate a new (random) tag value for PTR and tag the memory it
- points to upto the end of the usable size for the chunk containing
- it. Return the newly tagged pointer. */
-static void *
-__mtag_tag_new_usable (void *ptr)
-{
- if (ptr)
- {
- mchunkptr cp = mem2chunk(ptr);
- ptr = __libc_mtag_tag_region (__libc_mtag_new_tag (ptr),
- CHUNK_AVAILABLE_SIZE (cp) - CHUNK_HDR_SZ);
- }
- return ptr;
-}
-
-/* Generate a new (random) tag value for PTR, set the tags for the
- memory to the new tag and initialize the memory contents to VAL.
- In practice this function will only be called with VAL=0, but we
- keep this parameter to maintain the same prototype as memset. */
-static void *
-__mtag_tag_new_memset (void *ptr, int val, size_t size)
-{
- return __libc_mtag_memset_with_tag (__libc_mtag_new_tag (ptr), val, size);
-}
-#endif
-
static void
ptmalloc_init (void)
{
@@ -332,11 +304,8 @@ ptmalloc_init (void)
if (__MTAG_SBRK_UNTAGGED)
__morecore = __failing_morecore;
+ mtag_enabled = true;
mtag_mmap_flags = __MTAG_MMAP_FLAGS;
- tag_new_memset = __mtag_tag_new_memset;
- tag_region = __libc_mtag_tag_region;
- tag_new_usable = __mtag_tag_new_usable;
- tag_at = __libc_mtag_address_get_tag;
mtag_granule_mask = ~(size_t)(__MTAG_GRANULE_SIZE - 1);
}
#endif
diff --git a/malloc/malloc.c b/malloc/malloc.c
index e5f520267b..caf34843f7 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -441,35 +441,41 @@ void *(*__morecore)(ptrdiff_t) = __default_morecore;
*/
#ifdef USE_MTAG
+static bool mtag_enabled = false;
+static int mtag_mmap_flags = 0;
+static size_t mtag_granule_mask = ~(size_t)0;
+#else
+# define mtag_enabled false
+# define mtag_mmap_flags 0
+#endif
-/* Default implementaions when memory tagging is supported, but disabled. */
-static void *
-__default_tag_region (void *ptr, size_t size)
+static __always_inline void *
+tag_region (void *ptr, size_t size)
{
+ if (__glibc_unlikely (mtag_enabled))
+ return __libc_mtag_tag_region (ptr, size);
return ptr;
}
-static void *
-__default_tag_nop (void *ptr)
+static __always_inline void *
+tag_new_memset (void *ptr, int val, size_t size)
{
- return ptr;
+ if (__glibc_unlikely (mtag_enabled))
+ return __libc_mtag_memset_with_tag (__libc_mtag_new_tag (ptr), val, size);
+ return memset (ptr, val, size);
}
-static int mtag_mmap_flags = 0;
-static size_t mtag_granule_mask = ~(size_t)0;
-
-static void *(*tag_new_memset)(void *, int, size_t) = memset;
-static void *(*tag_region)(void *, size_t) = __default_tag_region;
-static void *(*tag_new_usable)(void *) = __default_tag_nop;
-static void *(*tag_at)(void *) = __default_tag_nop;
+/* Defined later. */
+static void *
+tag_new_usable (void *ptr);
-#else
-# define mtag_mmap_flags 0
-# define tag_new_memset(ptr, val, size) memset (ptr, val, size)
-# define tag_region(ptr, size) (ptr)
-# define tag_new_usable(ptr) (ptr)
-# define tag_at(ptr) (ptr)
-#endif
+static __always_inline void *
+tag_at (void *ptr)
+{
+ if (__glibc_unlikely (mtag_enabled))
+ return __libc_mtag_address_get_tag (ptr);
+ return ptr;
+}
#include <string.h>
@@ -3185,6 +3191,18 @@ tcache_thread_shutdown (void)
#endif /* !USE_TCACHE */
+static __always_inline void *
+tag_new_usable (void *ptr)
+{
+ if (__glibc_unlikely (mtag_enabled) && ptr)
+ {
+ mchunkptr cp = mem2chunk(ptr);
+ ptr = __libc_mtag_tag_region (__libc_mtag_new_tag (ptr),
+ CHUNK_AVAILABLE_SIZE (cp) - CHUNK_HDR_SZ);
+ }
+ return ptr;
+}
+
void *
__libc_malloc (size_t bytes)
{
--
2.17.1
next prev parent reply other threads:[~2021-03-04 16:32 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-04 16:30 [PATCH 00/16] memory tagging improvements Szabolcs Nagy
2021-03-04 16:30 ` [PATCH 01/16] malloc: Fix a realloc crash with heap tagging [BZ 27468] Szabolcs Nagy
2021-03-05 0:15 ` DJ Delorie
2021-03-05 12:01 ` Szabolcs Nagy
2021-03-05 18:42 ` DJ Delorie
2021-03-05 20:51 ` DJ Delorie
2021-03-04 16:30 ` [PATCH 02/16] Remove PR_TAGGED_ADDR_ENABLE from sys/prctl.h Szabolcs Nagy
2021-03-26 11:29 ` Szabolcs Nagy
2021-04-13 8:37 ` Szabolcs Nagy
2021-04-13 21:32 ` DJ Delorie
2021-03-04 16:31 ` [PATCH 03/16] malloc: Move MTAG_MMAP_FLAGS definition Szabolcs Nagy
2021-03-05 1:07 ` DJ Delorie
2021-03-04 16:31 ` [PATCH 04/16] malloc: Simplify __mtag_tag_new_usable Szabolcs Nagy
2021-03-05 0:20 ` DJ Delorie
2021-03-05 12:24 ` Szabolcs Nagy
2021-03-05 18:52 ` DJ Delorie
2021-03-04 16:31 ` [PATCH 05/16] malloc: Avoid taggig mmaped memory on free Szabolcs Nagy
2021-03-05 1:01 ` DJ Delorie
2021-03-04 16:31 ` [PATCH 06/16] malloc: Ensure the generic mtag hooks are not used Szabolcs Nagy
2021-03-05 1:05 ` DJ Delorie
2021-03-05 12:44 ` Szabolcs Nagy
2021-03-05 20:30 ` DJ Delorie
2021-03-04 16:32 ` [PATCH 07/16] malloc: Refactor TAG_ macros to avoid indirection Szabolcs Nagy
2021-03-05 0:28 ` DJ Delorie
2021-03-04 16:32 ` Szabolcs Nagy [this message]
2021-03-05 0:46 ` [PATCH 08/16] malloc: Use global flag instead of function pointer dispatch for mtag DJ Delorie
2021-03-05 12:53 ` Szabolcs Nagy
2021-03-04 16:32 ` [PATCH 09/16] malloc: Only support zeroing and not arbitrary memset with mtag Szabolcs Nagy
2021-03-05 0:49 ` DJ Delorie
2021-03-04 16:33 ` [PATCH 10/16] malloc: Change calloc when tagging is disabled Szabolcs Nagy
2021-03-05 1:06 ` DJ Delorie
2021-03-04 16:33 ` [PATCH 11/16] malloc: Use branches instead of mtag_granule_mask Szabolcs Nagy
2021-03-05 21:00 ` DJ Delorie
2021-03-04 16:33 ` [PATCH 12/16] malloc: Use mtag_enabled instead of USE_MTAG Szabolcs Nagy
2021-03-05 0:56 ` DJ Delorie
2021-03-04 16:34 ` [PATCH 13/16] aarch64: inline __libc_mtag_address_get_tag Szabolcs Nagy
2021-03-04 16:34 ` [PATCH 14/16] aarch64: inline __libc_mtag_new_tag Szabolcs Nagy
2021-03-04 16:34 ` [PATCH 15/16] aarch64: Optimize __libc_mtag_tag_region Szabolcs Nagy
2021-03-04 16:34 ` [PATCH 16/16] aarch64: Optimize __libc_mtag_tag_zero_region Szabolcs Nagy
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=8d9711a654bfe7a47ba743ab7e836118f8866f66.1614874816.git.szabolcs.nagy@arm.com \
--to=szabolcs.nagy@arm.com \
--cc=Richard.Earnshaw@arm.com \
--cc=dj@redhat.com \
--cc=libc-alpha@sourceware.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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 read-only IMAP folder(s) and NNTP newsgroup(s).