Prelinking does not work with uClibc anymore?

Yann Sionneau ysionneau at sequans.com
Fri Jan 24 15:00:33 UTC 2014


Hello,

I am trying to get prelinking to work on a MIPS target.
I reproduced the issue on OpenWRT (master branch, using uClibc-0.9.33.2) 
using the "MIPS Malta CoreLV board (qemu)" Target System.
At first uClibc Standalone Support was disabled leading to this when 
trying to run the dynamic linker as an executable:

root at OpenWrt:/# /lib/ld-uClibc.so.0
Standalone execution is not enabled

Then I enabled the following options in uClibc configuration:

LDSO_STANDALONE_SUPPORT=y
LDSO_PRELINK_SUPPORT=y

Afterward I get this when running the dynamic linker as an executable 
which means the standalone support has been enabled successfully:

root at OpenWrt:/# /lib/ld-uClibc.so.0
root at OpenWrt:/#

Then here comes the issue:

root at OpenWrt:/# LD_WARN= LD_TRACE_PRELINKING=1 LD_TRACE_LOADED_OBJECTS=1 
/lib/ld-uClibc.so.0 /bin/busybox
root at OpenWrt:/#

This should (should it?) print the list of libraries that busybox 
depends on (at least eglibc does that on x86), but here it prints nothing.
However, if running directly busybox with those environment variables I 
get what I wanted:

root at OpenWrt:/# LD_WARN= LD_TRACE_PRELINKING=1 LD_TRACE_LOADED_OBJECTS=1 
/bin/busybox
     /bin/busybox => /bin/busybox (0x400000, 0x0)
     libcrypt.so.0 => /lib/libcrypt.so.0 (0x77c19000, 0x77c19000)
     libm.so.0 => /lib/libm.so.0 (0x77bf4000, 0x77bf4000)
     libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x77bd0000, 0x77bd0000)
     libc.so.0 => /lib/libc.so.0 (0x77b63000, 0x77b63000) TLS(0x1, 0x0)
     ld-uClibc.so.0 => /lib/ld-uClibc.so.0 (0x77c3d000, 0x77c3d000)

Unfortunately, the prelink tool seems to depend on the eglibc behaviour 
which is to print those messages even if the dynamic linker is called as 
an executable, therefore I get those errors when trying to prelink:

root at OpenWrt:/# cat /etc/prelink.conf
-l /lib
-l /usr/lib
-l /bin
-l /sbin
-l /usr/bin
-l /usr/sbin
root at OpenWrt:/# prelink -c /etc/prelink.conf -C /etc/prelink.cache 
--dynamic-linker=/lib/ld-uClibc.so.0 -mvR --ld-library-path=/lib:/usr/lib -a
prelink: /bin/ubus seen 0 times in LD_TRACE_PRELINKING output, expected once
prelink: /bin/busybox seen 0 times in LD_TRACE_PRELINKING output, 
expected once
[...] etc

By looking at prelink source code (src/gather.c) I can see that indeed 
prelink tries to execute "LD_WARN= LD_TRACE_PRELINKING=1 
LD_TRACE_LOADED_OBJECTS=1 /lib/ld-uClibc.so.0 /bin/busybox" and then 
tries to parse the output to get the dependencies:

   argv[i++] = ent_filename;
   argv[i] = NULL;
   envp[0] = "LD_TRACE_LOADED_OBJECTS=1";
   envp[1] = "LD_TRACE_PRELINKING=1";
   envp[2] = "LD_WARN=";
   envp[3] = NULL;
   f = execve_open (dl, (char * const *)argv, (char * const *)envp);

Does anyone encounter this issue as well? Is there a known fix?

Thanks :)

PS: I am using prelink-20130503

Regards,

-- 
Yann Sionneau


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