From: Miroslav Lichvar <mlichvar@redhat.com>
Date: Wed, 3 Aug 2022 11:17:42 +0000 (+0200)
Subject: configure: disable arc4random on Linux
X-Git-Tag: 4.3-pre1~3
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d91ae2094fa87094430392acd9fd54b4132ba9f1;p=thirdparty%2Fchrony.git

configure: disable arc4random on Linux

In glibc 2.36 was added the arc4random family of functions. However,
unlike on other supported systems, it is not a user-space PRNG
implementation. It just wraps the getrandom() system call with no
buffering, which causes a performance loss on NTP servers due to
the function being called twice for each response to add randomness
to the RX and TX timestamp below the clock precision.

Don't check for arc4random on Linux to keep using the buffered
getrandom().
---

diff --git a/configure b/configure
index ed230f39..fd777c8e 100755
--- a/configure
+++ b/configure
@@ -245,6 +245,7 @@ try_lockmem=0
 feat_asyncdns=1
 feat_forcednsretry=1
 try_clock_gettime=1
+try_arc4random=1
 try_recvmmsg=1
 feat_timestamping=1
 try_timestamping=0
@@ -421,6 +422,7 @@ case $OPERATINGSYSTEM in
         try_setsched=1
         try_lockmem=1
         try_phc=1
+        try_arc4random=0
         add_def LINUX
         echo "Configuring for " $SYSTEM
     ;;
@@ -702,8 +704,10 @@ then
   use_pthread=1
 fi
 
-if test_code 'arc4random_buf()' 'stdlib.h' '' '' \
-    'arc4random_buf((void *)1, 1);'; then
+if [ $try_arc4random = "1" ] && \
+  test_code 'arc4random_buf()' 'stdlib.h' '' '' \
+    'arc4random_buf((void *)1, 1);'
+then
   add_def HAVE_ARC4RANDOM
 else
   if test_code 'getrandom()' 'stdlib.h sys/random.h' '' '' \