[arch-general] /usr is not mounted. This is not supported.

[clemens fischer]

Thomas Bächler wrote:

> Am 27.10.2011 10:38, schrieb clemens fischer:
>
>> minilogd requires the following libs:
>>
>> -rwxr-xr-x 1 root root 11K Oct 18 18:34 /usr/sbin/minilogd lrwxrwxrwx
>> 1 root root 12 Sep 9 01:23 /usr/lib32/libc.so.6 -> libc-2.14.so
>> -rwxr-xr-x 1 root root 1.4M Sep 9 01:23 /usr/lib32/libc-2.14.so
>> /usr/lib32/libc.so.6: lrwxrwxrwx 1 root root 26 Sep 9 01:23
>> /lib/ld-linux.so.2 -> ../usr/lib32/ld-linux.so.2 -rwxr-xr-x 1 root
>> root 141K Sep 9 01:23 /usr/lib32/ld-2.14.so
>>
>> I don't know why it asks for libs out of usr/lib32, this output is
>> from (the recursive use of) readelf(1).  This is on a 64bit PC.
>
> Where do you get that from?
>
> $ ldd /usr/sbin/minilogd
>        linux-vdso.so.1 =>  (0x00007fff09d0c000)
>        libc.so.6 => /lib/libc.so.6 (0x00007f9c3fc9b000)
>        /lib/ld-linux-x86-64.so.2 (0x00007f9c40022000)
> $ readelf -d /usr/sbin/minilogd | grep library
> 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]

I'm really glad you asked!  I have a script called "missing-libs.sh",
and quite a number of self compiled programs.  Whenever pacman upgrades
my system, some libs required by my programs may vanish, so
"missing-libs.sh" is used to scan my entire
usr/local/{{s,}bin,lib,libexec} recursively to check that the programs
get to keep their dependencies.  It uses "readelf -d" instead of ldd(1),
because the latter actually runs any binary, which I can't afford for
security reasons.  Readelf prints a "NEEDED" entry for dependencies
besides other info, but (normally) without a path, so the script has an
init stage where all libs reported by "ldconfig -p" are cashed in an
array to have path info at hand.  I have to do this, because some lib
may require further libs which have to be checked recursively.

$ readelf -d /usr/sbin/minilogd

Dynamic section at offset 0x1e50 contains 20 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)  Shared library: [libc.so.6]
 ...
$ readelf -d /lib/libc.so.6

Dynamic section at offset 0x159b40 contains 27 entries:
  Tag        Type                         Name/Value
 0x0000000000000001 (NEEDED)  Shared library: [ld-linux-x86-64.so.2]
 ...

"ld-linux-x86-64.so.2" had no entry "NEEDED", so my script stops there.

Now your question points out a bug:  the first lib found is displayed,
and this may be a 32bit lib!  I'll have to come up with a fix for that
that avoids ldd(1).  My system was converted from 32 bit to 64 bit not
long ago, the script had been working for so long, it just didn't cross
my mind that the caching was at fault.

I just see that:

$ readelf -h /usr/sbin/minilogd
ELF Header:
  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
  Class:                             ELF64
  ...

So I'll have to account for that "Class" attribute of binaries.  Oh
well, I need to avoid ldd, so it has to be done.  Hmm, unless I can
efficiently sandbox ldd, entire directories need to be scanned afterall
...


clemens