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212 lines
7.1 KiB
212 lines
7.1 KiB
2 years ago
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commit 359653aaacad463d916323f03c0ac3c47405aafa
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Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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Date: Wed Jan 16 18:10:56 2019 +0000
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Do not use HP_TIMING_NOW for random bits
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This patch removes the HP_TIMING_BITS usage for fast random bits and replace
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with clock_gettime (CLOCK_MONOTONIC). It has unspecified starting time and
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nano-second accuracy, so its randomness is significantly better than
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gettimeofday.
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Althoug it should incur in more overhead (specially for architecture that
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support hp-timing), the symbol is also common implemented as a vDSO.
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Checked on aarch64-linux-gnu, x86_64-linux-gnu, and i686-linux-gnu. I also
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checked on a i686-gnu build.
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* include/random-bits.h: New file.
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* resolv/res_mkquery.c [HP_TIMING_AVAIL] (RANDOM_BITS,
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(__res_context_mkquery): Remove usage hp-timing usage and replace with
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random_bits.
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* resolv/res_send.c [HP_TIMING_AVAIL] (nameserver_offset): Likewise.
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* sysdeps/posix/tempname.c [HP_TIMING_AVAIL] (__gen_tempname):
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Likewise.
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diff --git a/include/random-bits.h b/include/random-bits.h
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new file mode 100644
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index 0000000000000000..a0651a5a34f80a8d
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--- /dev/null
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+++ b/include/random-bits.h
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@@ -0,0 +1,41 @@
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+/* Fast pseudo-random bits based on clock_gettime.
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+ Copyright (C) 2019 Free Software Foundation, Inc.
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+ This file is part of the GNU C Library.
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+
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+ The GNU C Library is free software; you can redistribute it and/or
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+ modify it under the terms of the GNU Lesser General Public
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+ License as published by the Free Software Foundation; either
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+ version 2.1 of the License, or (at your option) any later version.
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+
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+ The GNU C Library is distributed in the hope that it will be useful,
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+ but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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+ Lesser General Public License for more details.
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+
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+ You should have received a copy of the GNU Lesser General Public
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+ License along with the GNU C Library; if not, see
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+ <http://www.gnu.org/licenses/>. */
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+
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+#ifndef _RANDOM_BITS_H
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+# define _RANDOM_BITS_H
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+
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+#include <time.h>
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+#include <stdint.h>
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+
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+/* Provides fast pseudo-random bits through clock_gettime. It has unspecified
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+ starting time, nano-second accuracy, its randomness is significantly better
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+ than gettimeofday, and for mostly architectures it is implemented through
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+ vDSO instead of a syscall. Since the source is a system clock, the upper
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+ bits will have less entropy. */
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+static inline uint32_t
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+random_bits (void)
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+{
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+ struct timespec tv;
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+ __clock_gettime (CLOCK_MONOTONIC, &tv);
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+ /* Shuffle the lower bits to minimize the clock bias. */
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+ uint32_t ret = tv.tv_nsec ^ tv.tv_sec;
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+ ret ^= (ret << 24) | (ret >> 8);
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+ return ret;
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+}
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+
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+#endif
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diff --git a/resolv/res_mkquery.c b/resolv/res_mkquery.c
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index 213abeefadf7ece5..4471a8838b1de7ee 100644
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--- a/resolv/res_mkquery.c
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+++ b/resolv/res_mkquery.c
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@@ -82,6 +82,7 @@
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* SOFTWARE.
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*/
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+#include <stdint.h>
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#include <sys/types.h>
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#include <sys/param.h>
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#include <netinet/in.h>
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@@ -92,12 +93,7 @@
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#include <string.h>
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#include <sys/time.h>
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#include <shlib-compat.h>
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-
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-#include <hp-timing.h>
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-#include <stdint.h>
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-#if HP_TIMING_AVAIL
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-# define RANDOM_BITS(Var) { uint64_t v64; HP_TIMING_NOW (v64); Var = v64; }
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-#endif
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+#include <random-bits.h>
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int
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__res_context_mkquery (struct resolv_context *ctx, int op, const char *dname,
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@@ -120,16 +116,7 @@ __res_context_mkquery (struct resolv_context *ctx, int op, const char *dname,
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/* We randomize the IDs every time. The old code just incremented
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by one after the initial randomization which still predictable if
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the application does multiple requests. */
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- int randombits;
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-#ifdef RANDOM_BITS
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- RANDOM_BITS (randombits);
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-#else
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- struct timeval tv;
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- __gettimeofday (&tv, NULL);
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- randombits = (tv.tv_sec << 8) ^ tv.tv_usec;
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-#endif
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-
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- hp->id = randombits;
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+ hp->id = random_bits ();
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hp->opcode = op;
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hp->rd = (ctx->resp->options & RES_RECURSE) != 0;
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hp->rcode = NOERROR;
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diff --git a/resolv/res_send.c b/resolv/res_send.c
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index ac19627634281c2f..55e7fa438e7baac1 100644
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--- a/resolv/res_send.c
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+++ b/resolv/res_send.c
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@@ -109,7 +109,7 @@
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#include <unistd.h>
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#include <kernel-features.h>
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#include <libc-diag.h>
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-#include <hp-timing.h>
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+#include <random-bits.h>
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#if PACKETSZ > 65536
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#define MAXPACKET PACKETSZ
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@@ -309,15 +309,7 @@ nameserver_offset (struct __res_state *statp)
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if ((offset & 1) == 0)
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{
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/* Initialization is required. */
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-#if HP_TIMING_AVAIL
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- uint64_t ticks;
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- HP_TIMING_NOW (ticks);
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- offset = ticks;
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-#else
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- struct timeval tv;
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- __gettimeofday (&tv, NULL);
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- offset = ((tv.tv_sec << 8) ^ tv.tv_usec);
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-#endif
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+ offset = random_bits ();
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/* The lowest bit is the most random. Preserve it. */
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offset <<= 1;
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diff --git a/sysdeps/posix/tempname.c b/sysdeps/posix/tempname.c
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index 432262a03b6ecc23..3d26f378021680ae 100644
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--- a/sysdeps/posix/tempname.c
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+++ b/sysdeps/posix/tempname.c
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@@ -71,22 +71,15 @@
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#endif
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#ifdef _LIBC
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-# include <hp-timing.h>
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-# if HP_TIMING_AVAIL
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-# define RANDOM_BITS(Var) \
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- if (__glibc_unlikely (value == UINT64_C (0))) \
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- { \
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- /* If this is the first time this function is used initialize \
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- the variable we accumulate the value in to some somewhat \
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- random value. If we'd not do this programs at startup time \
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- might have a reduced set of possible names, at least on slow \
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- machines. */ \
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- struct timeval tv; \
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- __gettimeofday (&tv, NULL); \
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- value = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec; \
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- } \
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- HP_TIMING_NOW (Var)
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-# endif
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+# include <random-bits.h>
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+# define RANDOM_BITS(Var) ((Var) = random_bits ())
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+# else
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+# define RANDOM_BITS(Var) \
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+ { \
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+ struct timeval tv; \
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+ __gettimeofday (&tv, NULL); \
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+ (Var) = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec; \
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+ }
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#endif
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/* Use the widest available unsigned type if uint64_t is not
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@@ -193,8 +186,7 @@ __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
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{
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int len;
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char *XXXXXX;
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- static uint64_t value;
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- uint64_t random_time_bits;
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+ uint64_t value;
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unsigned int count;
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int fd = -1;
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int save_errno = errno;
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@@ -227,16 +219,8 @@ __gen_tempname (char *tmpl, int suffixlen, int flags, int kind)
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XXXXXX = &tmpl[len - 6 - suffixlen];
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/* Get some more or less random data. */
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-#ifdef RANDOM_BITS
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- RANDOM_BITS (random_time_bits);
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-#else
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- {
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- struct timeval tv;
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- __gettimeofday (&tv, NULL);
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- random_time_bits = ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec;
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- }
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-#endif
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- value += random_time_bits ^ __getpid ();
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+ RANDOM_BITS (value);
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+ value ^= (uint64_t)__getpid () << 32;
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for (count = 0; count < attempts; value += 7777, ++count)
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{
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