Patchwork [4/6] Do not use HP_TIMING_NOW for random bits

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Submitter Adhemerval Zanella Netto
Date Feb. 8, 2019, 6:39 p.m.
Message ID <20190208183910.30799-4-adhemerval.zanella@linaro.org>
Download mbox | patch
Permalink /patch/31365/
State New
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Comments

Adhemerval Zanella Netto - Feb. 8, 2019, 6:39 p.m.
This patch removes the HP_TIMING_BITS usage for fast random bits and replace
with clock_gettime (CLOCK_MONOTONIC).  It has unspecified starting time and
nano-second accuracy, so its randomness is significantly better than
gettimeofday.

Althoug it should incur in more overhead (specially for architecture that
support hp-timing), the symbol is also common implemented as a vDSO.

Checked on aarch64-linux-gnu, x86_64-linux-gnu, and i686-linux-gnu. I also
checked on a i686-gnu build.

	* include/random-bits.h: New file.
	* resolv/res_mkquery.c [HP_TIMING_AVAIL] (RANDOM_BITS,
	(__res_context_mkquery): Remove usage hp-timing usage and replace with
	random_bits.
	* resolv/res_send.c [HP_TIMING_AVAIL] (nameserver_offset): Likewise.
	* sysdeps/posix/tempname.c [HP_TIMING_AVAIL] (__gen_tempname):
	Likewise.
---
 include/random-bits.h    | 37 +++++++++++++++++++++++++++++++++++++
 resolv/res_mkquery.c     | 19 +++----------------
 resolv/res_send.c        | 12 ++----------
 sysdeps/posix/tempname.c | 18 ++----------------
 4 files changed, 44 insertions(+), 42 deletions(-)
 create mode 100644 include/random-bits.h

Patch

diff --git a/include/random-bits.h b/include/random-bits.h
new file mode 100644
index 0000000000..81e6a50b5e
--- /dev/null
+++ b/include/random-bits.h
@@ -0,0 +1,37 @@ 
+/* Fast pseudo-random bits based on clock_gettime.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _RANDOM_BITS_H
+# define _RANDOM_BITS_H
+
+#include <time.h>
+#include <stdint.h>
+
+/* Provides fast pseudo-random bits through clock_gettime.  It has unspecified
+   starting time, nano-second accuracy, its randomness is significantly better
+   than gettimeofday, and for mostly architectures it is implemented through
+   vDSO instead of a syscall.  */
+static inline uint64_t
+random_bits (void)
+{
+  struct timespec tv;
+  __clock_gettime (CLOCK_MONOTONIC, &tv);
+  return tv.tv_nsec + UINT64_C(1000000000) * tv.tv_sec;
+}
+
+#endif
diff --git a/resolv/res_mkquery.c b/resolv/res_mkquery.c
index 19b8b402c4..dd43d347af 100644
--- a/resolv/res_mkquery.c
+++ b/resolv/res_mkquery.c
@@ -82,6 +82,7 @@ 
  * SOFTWARE.
  */
 
+#include <stdint.h>
 #include <sys/types.h>
 #include <sys/param.h>
 #include <netinet/in.h>
@@ -92,12 +93,7 @@ 
 #include <string.h>
 #include <sys/time.h>
 #include <shlib-compat.h>
-
-#include <hp-timing.h>
-#include <stdint.h>
-#if HP_TIMING_AVAIL
-# define RANDOM_BITS(Var) { uint64_t v64; HP_TIMING_NOW (v64); Var = v64; }
-#endif
+#include <random-bits.h>
 
 int
 __res_context_mkquery (struct resolv_context *ctx, int op, const char *dname,
@@ -120,16 +116,7 @@  __res_context_mkquery (struct resolv_context *ctx, int op, const char *dname,
   /* We randomize the IDs every time.  The old code just incremented
      by one after the initial randomization which still predictable if
      the application does multiple requests.  */
-  int randombits;
-#ifdef RANDOM_BITS
-  RANDOM_BITS (randombits);
-#else
-  struct timeval tv;
-  __gettimeofday (&tv, NULL);
-  randombits = (tv.tv_sec << 8) ^ tv.tv_usec;
-#endif
-
-  hp->id = randombits;
+  hp->id = random_bits ();
   hp->opcode = op;
   hp->rd = (ctx->resp->options & RES_RECURSE) != 0;
   hp->rcode = NOERROR;
diff --git a/resolv/res_send.c b/resolv/res_send.c
index fa040c1198..1b59b6080c 100644
--- a/resolv/res_send.c
+++ b/resolv/res_send.c
@@ -109,7 +109,7 @@ 
 #include <unistd.h>
 #include <kernel-features.h>
 #include <libc-diag.h>
-#include <hp-timing.h>
+#include <random-bits.h>
 
 #if PACKETSZ > 65536
 #define MAXPACKET       PACKETSZ
@@ -309,15 +309,7 @@  nameserver_offset (struct __res_state *statp)
   if ((offset & 1) == 0)
     {
       /* Initialization is required.  */
-#if HP_TIMING_AVAIL
-      uint64_t ticks;
-      HP_TIMING_NOW (ticks);
-      offset = ticks;
-#else
-      struct timeval tv;
-      __gettimeofday (&tv, NULL);
-      offset = ((tv.tv_sec << 8) ^ tv.tv_usec);
-#endif
+      offset = random_bits ();
       /* The lowest bit is the most random.  Preserve it.  */
       offset <<= 1;
 
diff --git a/sysdeps/posix/tempname.c b/sysdeps/posix/tempname.c
index 2ed39d1a42..62a20b3f30 100644
--- a/sysdeps/posix/tempname.c
+++ b/sysdeps/posix/tempname.c
@@ -71,22 +71,8 @@ 
 #endif
 
 #ifdef _LIBC
-# include <hp-timing.h>
-# if HP_TIMING_AVAIL
-#  define RANDOM_BITS(Var) \
-  if (__glibc_unlikely (value == UINT64_C (0)))				      \
-    {									      \
-      /* If this is the first time this function is used initialize	      \
-	 the variable we accumulate the value in to some somewhat	      \
-	 random value.  If we'd not do this programs at startup time	      \
-	 might have a reduced set of possible names, at least on slow	      \
-	 machines.  */							      \
-      struct timeval tv;						      \
-      __gettimeofday (&tv, NULL);					      \
-      value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;		      \
-    }									      \
-  HP_TIMING_NOW (Var)
-# endif
+# include <random-bits.h>
+# define RANDOM_BITS(Var) ((Var) = random_bits ())
 #endif
 
 /* Use the widest available unsigned type if uint64_t is not