Library usage

So what does a binary depend on? Use ldd:

bilbo$ ldd /bin/ls
            librt.so.1 => /lib/tls/librt.so.1 (0x4001f000)
    libacl.so.1 => /lib/libacl.so.1 (0x40025000)
    libc.so.6 => /lib/tls/libc.so.6 (0x4002d000)
    libpthread.so.0 => /lib/tls/libpthread.so.0 (0x40168000)
    /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)
    libattr.so.1 => /lib/libattr.so.1 (0x40177000)

So how are they used? Use ltrace (not base):

bilbo$ ltrace /bin/ls
__libc_start_main(0x8049ea0, 1, 0xbffff554, 0x80561a0, 0x8056200 
setlocale(6, "")                                                             = "en_GB.UTF-8"
bindtextdomain("coreutils", "/usr/share/locale")                             = "/usr/share/locale"
textdomain("coreutils")                                                      = "coreutils"
__cxa_atexit(0x8052200, 0, 0, 0x8056540, 0xbffff4c8)                         = 0
isatty(1)                                                                    = 1
getenv("QUOTING_STYLE")                                                      = NULL
getenv("LS_BLOCK_SIZE")                                                      = NULL
getenv("BLOCK_SIZE")                                                         = NULL
getenv("POSIXLY_CORRECT")                                                    = NULL
getenv("BLOCK_SIZE")                                                         = NULL
getenv("COLUMNS")                                                            = NULL
ioctl(1, 21523, 0xbffff2b8)                                                  = 0
getenv("POSIXLY_CORRECT")                                                    = NULL
getenv("TABSIZE")                                                            = NULL
getopt_long(1, 0xbffff554, "abcdfghiklmnopqrstuvw:xABCDFGHI:"..., 0x8056860, NULL) = -1
__errno_location()                                                           = 0x4017b060
malloc(36)                                                                   = 0x805b858
__errno_location()                                                           = 0x4017b060
malloc(36)                                                                   = 0x805b880
malloc(12000)                                                                = 0x805b8a8
malloc(12)                                                                   = 0x805e790
strlen(".")                                                                  = 1
malloc(2)                                                                    = 0x805e7a0
memcpy(0x805e7a0, ".", 2)                                                    = 0x805e7a0
__errno_location()                                                           = 0x4017b060
opendir(".")                                                                 = 0x805e7b0
__errno_location()                                                           = 0x4017b060
readdir64(0x805e7b0)                                                         = 0x805e7cc
readdir64(0x805e7b0)                                                         = 0x805e7e4
readdir64(0x805e7b0)                                                         = NULL
closedir(0x805e7b0)                                                          = 0
_setjmp(0x805a5c0, 0x400a12b0, 0x40165800, 0x805e7b0, 0x40164e8c)            = 0
qsort(0x805b8a8, 0, 120, 0x804ce00)                                          = 
free(0x805e7a0)                                                              = 
free(0x805e790)                                                              = 
exit(0 
__fpending(0x4015dd40, 0x805a3a0, 0x400a23d8, 0x8048c10, 0x40165800)         = 0
+++ exited (status 0) +++