linux - How can I find which ELF dependency is not fulfilled?

Question

I've built a test ELF program using the LSB SDK (note that my question is not specific to LSB):

$ /opt/lsb/bin/lsbcc tst.c
$ ls -l a.out 
-rwxr-xr-x 1 math math 10791 2009-10-13 20:13 a.out
$ file a.out 
a.out: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.15, not stripped

But I am unable to launch it (yes, I assure you the file is in the directory...):

$ ./a.out 
bash: ./a.out: No such file or directory

$ uname -a
Linux math 2.6.28-15-generic #52-Ubuntu SMP Wed Sep 9 10:48:52 UTC 2009 x86_64 GNU/Linux

I think there is an ELF dependency which is not fulfill but I don't know how to find it. Is there a tool similar to ldd for libraries which can be used to found the missing link?

I don't think it is related to the 2.6.15/2.6.28-15 difference because the LSB compiler is working:

$ file /opt/lsb/bin/lsbcc 
/opt/lsb/bin/lsbcc: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.4, not stripped

Just in case, here is the ELF dynamic section of a.out:

 0x0000000000000001 (NEEDED)             Shared library: [libpthread.so.0]
 0x0000000000000001 (NEEDED)             Shared library: [libm.so.6]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x000000000000000c (INIT)               0x400428
 0x000000000000000d (FINI)               0x400638
 0x0000000000000004 (HASH)               0x400278
 0x0000000000000005 (STRTAB)             0x400350
 0x0000000000000006 (SYMTAB)             0x4002a8
 0x000000000000000a (STRSZ)              121 (bytes)
 0x000000000000000b (SYMENT)             24 (bytes)
 0x0000000000000015 (DEBUG)              0x0
 0x0000000000000003 (PLTGOT)             0x600fe8
 0x0000000000000002 (PLTRELSZ)           24 (bytes)
 0x0000000000000014 (PLTREL)             RELA
 0x0000000000000017 (JMPREL)             0x400410
 0x0000000000000007 (RELA)               0x4003f8
 0x0000000000000008 (RELASZ)             24 (bytes)
 0x0000000000000009 (RELAENT)            24 (bytes)
 0x000000006ffffffe (VERNEED)            0x4003d8
 0x000000006fffffff (VERNEEDNUM)         1
 0x000000006ffffff0 (VERSYM)             0x4003ca
 0x0000000000000000 (NULL)               0x0

Answer 1

This looks like what happens when the ELF interpreter is missing.

Ensure that /lib/ld-lsb.so.2 (or similar; varies by LSB version and architecture) exists. ldd and readelf -l will be able to show the ELF interpreter your executable is requesting.

(lsbcc (or something in the LSB toolchain) overrides the system's default /lib/ld-linux.so.2, probably by passing -Wl,--dynamic-linker=/lib/ld-lsb.so.2 to the compiler, for reasons I think are rather silly (Glibc has always provided fairly excellent backwards-compatibility here), but there you have it.)