Examples

A new utility, dump(1), makes it easier to debug object files or to check the static and dynamic linking, see "Backing Up and Restoring Files"). The dump -L option displays the information needed by the runtime linker that is contained in the executable. This information is contained in the dynamic section of an ELF file. The RPATH entry displays search paths specified by the -R option to ld.

The following example:

• Builds a shared library, libx.so.1, using libx.o

• Creates a link from libx.so.1 to libx.so

• Shows dump output, including the SONAME field, which stores the information passed with the -h option.

examples% cc -G -o libx.so.1 -h libx.so.1 libx.o

examples% cp libx.so.1 /mylibs
examples% ln -s /mylibs/libx.so.1 /mylibs/libx.so
examples% dump -Lv libx.so.1

libx.so.1:

  **** DYNAMIC SECTION INFORMATION ****
.dynamic :
[INDEX] Tag      Value
[1]     INIT     0x3b8
[2]     FINI     0x3f4
[3]     SONAME   libx.so.1
[4]     HASH     0x94
[5]     STRTAB   0x33c
[6]     SYMTAB   0x14c
[7]     STRSZ    0x62
[8]     SYMENT   0x10
[9]     PLTGOT   0x10404
[10]    PLTSZ    0xc
[11]    PLTREL   0x7
[12]    JMPREL   0x3ac
[13]    RELA     0x3a0
[14]    RELASZ   0x18
[15]    RELAENT  0xc

If a library needs other dynamic libraries, they should be specified along with an RPATH, as the next example shows.

The next example compiles prog.c, dynamically linking libx.so (as built in the previous example), and specifies that the binary retain the current directory information for execution. This example shows the output of dump from the compiled program, prog.c. Here, the information stored in the SONAME field of the previous example is shown as NEEDED by prog. When prog is run, it will use libx.so.1 even if libx.so is linked to a different version.

examples% cc -o prog prog.c -L/mylibs -R/mylibs -lx
example% dump -Lv prog

prog:

  **** DYNAMIC SECTION INFORMATION ****
.dynamic :
[INDEX]   Tag   Value
[1]  NEEDED   libx.so.1
[2]  NEEDED   libc.so.1
[3]  INIT     0x1b1ac
[4]  FINI     0x1b248
[5]  RPATH    /mylibs
[6]  HASH     0x100e8
[7]  STRTAB   0x17f90
[8]  SYMTAB   0x12be0
[9]  STRSZ    0x31e1
[10] SYMENT   0x10
[11] DEBUG    0x0
[12] PLTGOT   0x2b25c
[13] PLTSZ    0x30
[14] PLTREL   0x7
[15] JMPREL   0x1b180
[16] RELA     0x1b174
[17] RELASZ   0x3c
[18] RELAENT  0xc