Issues with Arc4random

Maarten Lankhorst m.b.lankhorst at
Fri Dec 30 15:24:01 PST 2005

I tried compiling a simple test program with arc4random (HLFS SVN-20051221):

#include <stdlib.h>
#include <stdio.h>

int main(void) {
 int random_number;
 random_number = arc4random() % 65536;
 printf("A random number between 0 and 65536 is %d\n", random_number);
 return 0;

/tmp/cceNQEwU.o: In function `main':
arc4random.c:(.text+0x34): undefined reference to `arc4random'
collect2: ld returned 1 exit status

To my surprise, it failed, first thing I did was seeing if it was the 
same for my HLFS host, and it was.

Since I was still in early chapter 6 phase, I redownloaded glibc source 
again, and applied patches.To see wether it should work or that I messed 
up somewhere, I carefully applied all patches, and found the first 
issue, SSP doesn't use arc4random in current book any more due to a 
wrong ifdef:

In glibc-2.3.6-ssp-1.patch:
+#if defined(HAVE_ARC4RANDOM) /* From <stdlib.h> */
should be
+#if defined(LIBC_HAS_ARC4RANDOM) /* From <stdlib.h> 
is the reason why SSP was wrong, it was probably overlooked.

Secondly, glibc wasn't actually exporting the arc4random* functions, by 
looking for all references to memfrob, I found out why:
The declarations in stdlib/Versions were missing in 
glibc-2.3.6-arc4random-1.patch, so I added them here:

--- glibc-2.3.6-old/stdlib/Versions     2004-05-03 23:25:53.000000000 +0200
+++ glibc-2.3.6/stdlib/Versions 2005-12-31 00:17:28.000000000 +0100
@@ -11,6 +11,8 @@

     # a*
     a64l; abort; abs; atexit; atof; atoi; atol; atoll;
+    arc4random_stir; arc4random_addrandom; arc4random;
+    arc4random_stirII; arc4random_addrandomII; arc4randomII;

     # b*

After recompiling glibc, and copying to /lib, my test program 
compiled correctly.

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