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MODULE 111-5

OTHER USEFUL GDB/GCC FRIENDS 5

 

 

 

 

 

 

 

My Training Period: xx hours

 

The ability:

  • Can play around and be familiar with ldd, readelf, od, size, strings, objcopy and strace.

 

Note:  The information start with the command and a list of options (including the sub-processes).  Then examples given how to use the commands and some of the options followed by the sample outputs.  Some of the outputs have been trimmed.  It is compiled from man page.  Run on Linux / Fedora Core 3.

 

The ldd - Printing Shared Libraries

 

ldd - list dynamic dependencies (DLLs)

ldd prints the shared libraries required by each program or shared library specified on the command line.

Usage: ldd [OPTION]  FILE

 

--help

print this help and exit

--version

print version information and exit

-d, --data-relocs

process data relocations

-r, --function-relocs

process data and function relocations

-u, --unused

print unused direct dependencies

-v, --verbose

print all information

 

Examples: testbuff is an executable file.

 

[bodo@bakawali testbed5]$ ldd -r -v testbuff

    libc.so.6 => /lib/tls/libc.so.6 (0x00675000)

    /lib/ld-linux.so.2 (0x00658000)

 

    Version information:

    ./testbuff:

     libc.so.6 (GLIBC_2.0) => /lib/tls/libc.so.6

    /lib/tls/libc.so.6:

     ld-linux.so.2 (GLIBC_2.1) => /lib/ld-linux.so.2

     ld-linux.so.2 (GLIBC_2.3) => /lib/ld-linux.so.2

     ld-linux.so.2 (GLIBC_PRIVATE) => /lib/ld-linux.so.2

     ld-linux.so.2 (GLIBC_2.0) => /lib/ld-linux.so.2

 

[bodo@bakawali testbed5]$ ldd -d -v testbuff

    libc.so.6 => /lib/tls/libc.so.6 (0x00675000)

    /lib/ld-linux.so.2 (0x00658000)

 

    Version information:

    ./testbuff:

     libc.so.6 (GLIBC_2.0) => /lib/tls/libc.so.6

    /lib/tls/libc.so.6:

     ld-linux.so.2 (GLIBC_2.1) => /lib/ld-linux.so.2

     ld-linux.so.2 (GLIBC_2.3) => /lib/ld-linux.so.2

     ld-linux.so.2 (GLIBC_PRIVATE) => /lib/ld-linux.so.2

     ld-linux.so.2 (GLIBC_2.0) => /lib/ld-linux.so.2

 

The readelf - Displaying The ELF Information

 

readelf

readelf displays information about the contents of one or more ELF format object files.   The options control what particular information to display.  elf files are the object files to be examined.  32-bit and 64-bit ELF files are supported, also archives containing ELF files.  This program performs a similar function to objdump but it goes into more detail and it exists independently of the BFD library, so if there is a bug in BFD then readelf will not be affected.

BFD – Binary File Descriptor.  Is a package which allows applications to use the same routines to operate on object files whatever the object file format (http://www.gnu.org/).

Usage: readelf <option(s)> elf-file(s)

Options are:

-a --all

Equivalent to: -h -l -S -s -r -d -V -A -I

-h --file-header

Display the ELF file header

-l --program-headers

Display the program headers

--segments

An alias for --program-headers

-S --section-headers

Display the sections' header

--sections

An alias for --section-headers

-g --section-groups

Display the section groups

-e --headers

Equivalent to: -h -l -S

-s --syms

Display the symbol table

--symbols

An alias for --syms

-n --notes

Display the core notes (if present)

-r --relocs

Display the relocations (if present)

-u --unwind

Display the unwind info (if present)

-d --dynamic

Display the dynamic section (if present)

-V --version-info

Display the version sections (if present)

-A --arch-specific

Display architecture specific information (if any).

-D --use-dynamic

Use the dynamic section info when displaying symbols

-x --hex-dump=<number>

Dump the contents of section <number>

-w[liaprmfFso] or --debug-dump[=line,

=info,=abbrev,=pubnames,=ranges,

=macro,=frames,=str,=loc]

Display the contents of DWARF2 debug sections

-I --histogram

Display histogram of bucket list lengths

-W --wide

Allow output width to exceed 80 characters

-H --help

Display this information

-v --version

Display the version number of readelf

 

Examples:

 

[bodo@bakawali testbed5]$ readelf -r testbuff.o

 

Relocation section '.rel.text' at offset 0x3d4 contains 5 entries:

 Offset     Info    Type            Sym.Value  Sym. Name

0000000a  00000501 R_386_32          00000000   .rodata

0000000f  00000902 R_386_PC32        00000000   printf

0000001e  00000a02 R_386_PC32        00000000   gets

0000002d  00000b02 R_386_PC32        00000000   puts

00000053  00000802 R_386_PC32        00000000   Test

 

[bodo@bakawali testbed5]$ readelf -r testbuff

 

Relocation section '.rel.dyn' at offset 0x298 contains 1 entries:

 Offset     Info    Type            Sym.Value  Sym. Name

08049600  00000706 R_386_GLOB_DAT    00000000   __gmon_start__

 

Relocation section '.rel.plt' at offset 0x2a0 contains 4 entries:

 Offset     Info    Type            Sym.Value  Sym. Name

08049610  00000107 R_386_JUMP_SLOT   00000000   gets

08049614  00000207 R_386_JUMP_SLOT   00000000   puts

08049618  00000307 R_386_JUMP_SLOT   00000000   __libc_start_main

0804961c  00000407 R_386_JUMP_SLOT   00000000   printf

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[bodo@bakawali testbed5]$ readelf -h testbuff.o

ELF Header:

  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00

  Class:                             ELF32

  Data:                              2's complement, little endian

  Version:                           1 (current)

  OS/ABI:                            UNIX - System V

  ABI Version:                       0

  Type:                              REL (Relocatable file)

  Machine:                           Intel 80386

  Version:                           0x1

  Entry point address:               0x0

  Start of program headers:          0 (bytes into file)

  Start of section headers:          292 (bytes into file)

  Flags:                             0x0

  Size of this header:               52 (bytes)

  Size of program headers:           0 (bytes)

  Number of program headers:         0

  Size of section headers:           40 (bytes)

  Number of section headers:         11

  Section header string table index: 8

 

[bodo@bakawali testbed5]$ readelf -h testbuff

ELF Header:

  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00

  Class:                             ELF32

  Data:                              2's complement, little endian

  Version:                           1 (current)

  OS/ABI:                            UNIX - System V

  ABI Version:                       0

  Type:                              EXEC (Executable file)

  Machine:                           Intel 80386

  Version:                           0x1

  Entry point address:               0x8048328

  Start of program headers:          52 (bytes into file)

  Start of section headers:          3116 (bytes into file)

  Flags:                             0x0

  Size of this header:               52 (bytes)

  Size of program headers:           32 (bytes)

  Number of program headers:         7

  Size of section headers:           40 (bytes)

  Number of section headers:         35

  Section header string table index: 32

 

[bodo@bakawali testbed5]$ readelf -s testbuff

 

Symbol table '.dynsym' contains 8 entries:

   Num:    Value  Size Type    Bind   Vis      Ndx Name

     0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND

     1: 00000000   357 FUNC    GLOBAL DEFAULT  UND gets@GLIBC_2.0 (2)

     2: 00000000   427 FUNC    GLOBAL DEFAULT  UND puts@GLIBC_2.0 (2)

     3: 00000000   239 FUNC    GLOBAL DEFAULT  UND __libc_start_main@GLIBC_2.0 (2)

     4: 00000000    54 FUNC    GLOBAL DEFAULT  UND printf@GLIBC_2.0 (2)

     5: 0804850c     4 OBJECT  GLOBAL DEFAULT   14 _IO_stdin_used

     6: 00000000     0 NOTYPE  WEAK   DEFAULT  UND _Jv_RegisterClasses

     7: 00000000     0 NOTYPE  WEAK   DEFAULT  UND __gmon_start__

 

Symbol table '.symtab' contains 80 entries:

   Num:    Value  Size Type    Bind   Vis      Ndx Name

     0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND

     1: 08048114     0 SECTION LOCAL  DEFAULT    1

     2: 08048128     0 SECTION LOCAL  DEFAULT    2

     3: 08048148     0 SECTION LOCAL  DEFAULT    3

     4: 0804817c     0 SECTION LOCAL  DEFAULT    4

     5: 080481fc     0 SECTION LOCAL  DEFAULT    5

     6: 08048266     0 SECTION LOCAL  DEFAULT    6

     7: 08048278     0 SECTION LOCAL  DEFAULT    7

     8: 08048298     0 SECTION LOCAL  DEFAULT    8

     9: 080482a0     0 SECTION LOCAL  DEFAULT    9

[omitted]

    17: 0804952c     0 SECTION LOCAL  DEFAULT   17

    18: 08049534     0 SECTION LOCAL  DEFAULT   18

    19: 08049538     0 SECTION LOCAL  DEFAULT   19

    20: 08049600     0 SECTION LOCAL  DEFAULT   20

    21: 08049604     0 SECTION LOCAL  DEFAULT   21

    22: 08049620     0 SECTION LOCAL  DEFAULT   22

    23: 0804962c     0 SECTION LOCAL  DEFAULT   23

    24: 00000000     0 SECTION LOCAL  DEFAULT   24

    [omitted]

    32: 00000000     0 SECTION LOCAL  DEFAULT   32

    33: 00000000     0 SECTION LOCAL  DEFAULT   33

    34: 00000000     0 SECTION LOCAL  DEFAULT   34

    35: 0804834c     0 FUNC    LOCAL  DEFAULT   12 call_gmon_start

    36: 00000000     0 FILE    LOCAL  DEFAULT  ABS crtstuff.c

    37: 08049524     0 OBJECT  LOCAL  DEFAULT   16 __CTOR_LIST__

    38: 0804952c     0 OBJECT  LOCAL  DEFAULT   17 __DTOR_LIST__

    39: 08049534     0 OBJECT  LOCAL  DEFAULT   18 __JCR_LIST__

    …

    [omitted]

   …

    73: 08049630     0 NOTYPE  GLOBAL DEFAULT  ABS _end

    74: 08049524     0 NOTYPE  GLOBAL HIDDEN  ABS __init_array_start

    75: 0804850c     4 OBJECT  GLOBAL DEFAULT   14 _IO_stdin_used

    76: 08049620     0 NOTYPE  GLOBAL DEFAULT   22 __data_start

    77: 00000000     0 NOTYPE  WEAK   DEFAULT  UND _Jv_RegisterClasses

    78: 08049524     0 NOTYPE  GLOBAL HIDDEN  ABS __preinit_array_start

    79: 00000000     0 NOTYPE  WEAK   DEFAULT  UND __gmon_start__

 

[bodo@bakawali testbed5]$ readelf -s testbuff.o

 

Symbol table '.symtab' contains 13 entries:

   Num:    Value  Size Type    Bind   Vis      Ndx Name

     0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND

     1: 00000000     0 FILE    LOCAL  DEFAULT  ABS testbuff.c

     2: 00000000     0 SECTION LOCAL  DEFAULT    1

     3: 00000000     0 SECTION LOCAL  DEFAULT    3

     4: 00000000     0 SECTION LOCAL  DEFAULT    4

     5: 00000000     0 SECTION LOCAL  DEFAULT    5

     6: 00000000     0 SECTION LOCAL  DEFAULT    6

     7: 00000000     0 SECTION LOCAL  DEFAULT    7

     8: 00000000    54 FUNC    GLOBAL DEFAULT    1 Test

     9: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND printf

    10: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND gets

    11: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND puts

    12: 00000036    40 FUNC    GLOBAL DEFAULT    1 main

 

[bodo@bakawali testbed5]$ readelf -l testbuff

 

Elf file type is EXEC (Executable file)

Entry point 0x8048328

There are 7 program headers, starting at offset 52

 

Program Headers:

  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align

  PHDR           0x000034 0x08048034 0x08048034 0x000e0 0x000e0 R E 0x4

  INTERP         0x000114 0x08048114 0x08048114 0x00013 0x00013 R   0x1

      [Requesting program interpreter: /lib/ld-linux.so.2]

  LOAD           0x000000 0x08048000 0x08048000 0x00524 0x00524 R E 0x1000

  LOAD           0x000524 0x08049524 0x08049524 0x00108 0x0010c RW  0x1000

  DYNAMIC        0x000538 0x08049538 0x08049538 0x000c8 0x000c8 RW  0x4

  NOTE           0x000128 0x08048128 0x08048128 0x00020 0x00020 R   0x4

  GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RW  0x4

 

 Section to Segment mapping:

  Segment Sections...

   00

   01     .interp

   02     .interp .note.ABI-tag .hash .dynsym .dynstr .gnu.version .gnu.version_r .rel.dyn .rel.plt .init .plt .text .fini .rodata .eh_frame

   03     .ctors .dtors .jcr .dynamic .got .got.plt .data .bss

   04     .dynamic

   05     .note.ABI-tag

   06

 

[bodo@bakawali testbed5]$ readelf -l testbuff | fgrep STACK

  GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RW  0x4

 

[bodo@bakawali testbed5]$ readelf -l testbuff | fgrep DYNAMIC

  DYNAMIC        0x000538 0x08049538 0x08049538 0x000c8 0x000c8 RW  0x4

 

[bodo@bakawali testbed5]$ readelf -l testbuff | fgrep .rodata

   02     .interp .note.ABI-tag .hash .dynsym .dynstr .gnu.version .gnu.version_r .rel.dyn .rel.plt .init .plt .text .fini .rodata .eh_frame

 

[bodo@bakawali testbed5]$ readelf -l testbuff | fgrep .got.plt

   03     .ctors .dtors .jcr .dynamic .got .got.plt .data .bss

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The od - Dumping File In Various Formats

 

od

od will dump files in octal and other formats.  Write an unambiguous representation, octal bytes by default, of a FILE to standard output.  With more than one FILE argument, concatenate them in the listed order to form the input.  With no FILE, or when FILE is -, read standard input.

Usage: od [OPTION]... [FILE]... or:  od --traditional [FILE] [[+]OFFSET [[+]LABEL]]

All arguments to long options are mandatory for short options.

-A, --address-radix=RADIX

decide how file offsets are printed

-j, --skip-bytes=BYTES

skip BYTES input bytes first

-N, --read-bytes=BYTES

limit dump to BYTES input bytes

-s, --strings[=BYTES]

output strings of at least BYTES graphic chars

-t, --format=TYPE

select output format or formats

-v, --output-duplicates

do not use * to mark line suppression

-w, --width[=BYTES]

output BYTES bytes per output line

--traditional

accept arguments in traditional form

--help

display this help and exit

--version

output version information and exit

Traditional format specifications may be intermixed; they accumulate:

-a   same as -t a

select named characters

-b   same as -t oC

select octal bytes

-c   same as -t c

select ASCII characters or backslash escapes

-d   same as -t u2

select unsigned decimal shorts

-f   same as -t fF

select floats

-h   same as -t x2

select hexadecimal shorts

-i   same as -t d2

select decimal shorts

-l   same as -t d4

select decimal longs

-o   same as -t o2

select octal shorts

-x   same as -t x2

select hexadecimal shorts

For older syntax (second call format), OFFSET means -j OFFSET.  LABEL is the pseudo-address at first byte printed, incremented when dump is progressing.  For OFFSET and LABEL, a 0x or 0X prefix indicates hexadecimal, suffixes may be for octal and b for multiply by 512.

TYPE is made up of one or more of these specifications:

a

named character

c

ASCII character or backslash escape

d[SIZE]

signed decimal, SIZE bytes per integer

f[SIZE]

floating point, SIZE bytes per integer

o[SIZE]

octal, SIZE bytes per integer

u[SIZE]

unsigned decimal, SIZE bytes per integer

x[SIZE]

hexadecimal, SIZE bytes per integer

SIZE is a number.  For TYPE in doux, SIZE may also be C for sizeof(char), S for sizeof(short), I for sizeof(int) or L for sizeof(long).  If TYPE is f, SIZE may also be F for sizeof(float), D for sizeof(double) or L for sizeof(long double).

RADIX is d for decimal, o for octal, x for hexadecimal or n for none.  BYTES is hexadecimal with 0x or 0X prefix, it is multiplied by 512 with b suffix, by 1024 with k and by 1048576 with m.  Adding a z suffix to any type adds a display of printable characters to the end of each line of output.  --string without a number implies 3.  --width without a number implies 32.  By default, od uses -A o -t d2 -w 16.

 

Examples:

 

[bodo@bakawali testbed5]$ od -s testbuff.o

0000224 Some input:

0000242 GCC: (GNU) 3.4.2 20041017 (Red Hat 3.4.2-6.fc3)

0000323 .symtab

0000333 .strtab

0000343 .shstrtab

0000355 .rel.text

0000367 .data

0000375 .bss

0000402 .rodata

0000412 .note.GNU-stack

0000432 .comment

0001655 testbuff.c

0001670 Test

0001675 printf

0001704 gets

0001711 puts

0001716 main

 

[bodo@bakawali testbed5]$ od -a testbuff.o

0000000 del   E   L   F soh soh soh nul nul nul nul nul nul nul nul nul

0000020 soh nul etx nul soh nul nul nul nul nul nul nul nul nul nul nul

0000040   $ soh nul nul nul nul nul nul   4 nul nul nul nul nul   ( nul

0000060  vt nul  bs nul   U  ht   e etx   l  bs etx   l  ff   h nul nul

0000100 nul nul   h   | del del del etx   D dle etx   l  ff  cr   E   |

0000120   P   h   | del del del etx   D dle etx   l  ff  cr   E   |   P

0000140   h   | del del del etx   D dle   I   C   U  ht   e etx   l  bs

0000160 etx   d   p   8 nul nul nul nul etx   @  si etx   @  si   A   h

0000200 eot   A   ` eot   )   D   h   | del del del   8 nul nul nul nul

0000220   I   C nul nul   S   o   m   e  sp   i   n   p   u   t   :  sp

0000240 nul nul   G   C   C   :  sp   (   G   N   U   )  sp   3   .   4

[omitted]

0000600 nul nul nul nul   T etx nul nul   ( nul nul nul  ht nul nul nul

0000620 soh nul nul nul eot nul nul nul  bs nul nul nul   % nul nul nul

0000640 soh nul nul nul etx nul nul nul nul nul nul nul dc4 nul nul nul

0000660 nul nul nul nul nul nul nul nul nul nul nul nul eot nul nul nul

[omitted]

....

....

 

 

 

 

 

 

 

 

 

 

 

 

Further related reading:

 

  1. Check the best selling C / C++, Networking, Linux and Open Source books at Amazon.com.

  2. Linux Socket programming tutorial.

  3. C, Buffer overflow and stack frame (construction and destruction).

  4. C, Compiler, Assembler and Linker.

 

 

 

 

 

|< Linux gnu, nm and objdump 4 | Linux gnu size, strings, objcopy, strace 6 >| Main | Site Index | Download |


C & Linux GNU Related Utilities:  Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6