4. objdump

objdump [‘-a’|‘--archive-headers’]
        [‘-b’ bfdname|‘--target=bfdname’]
        [‘-C’|‘--demangle’[=style] ]
        [‘-d’|‘--disassemble’]
        [‘-D’|‘--disassemble-all’]
        [‘-z’|‘--disassemble-zeroes’]
        [‘-EB’|‘-EL’|‘--endian=’{big | little }]
        [‘-f’|‘--file-headers’]
        [‘--file-start-context’]
        [‘-g’|‘--debugging’]
        [‘-e’|‘--debugging-tags’]
        [‘-h’|‘--section-headers’|‘--headers’]
        [‘-i’|‘--info’]
        [‘-j’ section|‘--section=’section]
        [‘-l’|‘--line-numbers’]
        [‘-S’|‘--source’]
        [‘-m’ machine|‘--architecture=’machine]
        [‘-M’ options|‘--disassembler-options=’options]
        [‘-p’|‘--private-headers’]
        [‘-r’|‘--reloc’]
        [‘-R’|‘--dynamic-reloc’]
        [‘-s’|‘--full-contents’]
        [‘-W’|‘--dwarf’]
        [‘-G’|‘--stabs’]
        [‘-t’|‘--syms’]
        [‘-T’|‘--dynamic-syms’]
        [‘-x’|‘--all-headers’]
        [‘-w’|‘--wide’]
        [‘--start-address=’address]
        [‘--stop-address=’address]
        [‘--prefix-addresses’]
        [‘--[no-]show-raw-insn’]
        [‘--adjust-vma=’offset]
        [‘--special-syms’]
        [‘-V’|‘--version’]
        [‘-H’|‘--help’]
        objfile…

objdump displays information about one or more object files. The options control what particular information to display. This information is mostly useful to programmers who are working on the compilation tools, as opposed to programmers who just want their program to compile and work.

objfile… are the object files to be examined. When you specify archives, objdump shows information on each of the member object files.

The long and short forms of options, shown here as alternatives, are equivalent. At least one option from the list ‘-a,-d,-D,-e,-f,-g,-G,-h,-H,-p,-r,-R,-s,-S,-t,-T,-V,-x’ must be given.

-a

--archive-header

If any of the objfile files are archives, display the archive header information (in a format similar to ‘ls -l’). Besides the information you could list with ‘ar tv’, ‘objdump -a’ shows the object file format of each archive member.

--adjust-vma=offset

When dumping information, first add offset to all the section addresses. This is useful if the section addresses do not correspond to the symbol table, which can happen when putting sections at particular addresses when using a format which can not represent section addresses, such as a.out.

-b bfdname

--target=bfdname

Specify that the object-code format for the object files is bfdname. This option may not be necessary; objdump can automatically recognize many formats.

For example,

objdump -b oasys -m vax -h fu.o

displays summary information from the section headers (‘-h’) of ‘fu.o’, which is explicitly identified (‘-m’) as a VAX object file in the format produced by Oasys compilers. You can list the formats available with the ‘-i’ option. See section Target Selection, for more information.

-C

--demangle[=style]

Decode (demangle) low-level symbol names into user-level names. Besides removing any initial underscore prepended by the system, this makes C++ function names readable. Different compilers have different mangling styles. The optional demangling style argument can be used to choose an appropriate demangling style for your compiler. See section c++filt, for more information on demangling.

-g

--debugging

Display debugging information. This attempts to parse debugging information stored in the file and print it out using a C like syntax. Only certain types of debugging information have been implemented. Some other types are supported by readelf -w. See section readelf.

-e

--debugging-tags

Like ‘-g’, but the information is generated in a format compatible with ctags tool.

-d

--disassemble

Display the assembler mnemonics for the machine instructions from objfile. This option only disassembles those sections which are expected to contain instructions.

-D

--disassemble-all

Like ‘-d’, but disassemble the contents of all sections, not just those expected to contain instructions.

--prefix-addresses

When disassembling, print the complete address on each line. This is the older disassembly format.

-EB

-EL

--endian={big|little}

Specify the endianness of the object files. This only affects disassembly. This can be useful when disassembling a file format which does not describe endianness information, such as S-records.

-f

--file-headers

Display summary information from the overall header of each of the objfile files.

--file-start-context

Specify that when displaying interlisted source code/disassembly (assumes ‘-S’) from a file that has not yet been displayed, extend the context to the start of the file.

-h

--section-headers

--headers

Display summary information from the section headers of the object file.

File segments may be relocated to nonstandard addresses, for example by using the ‘-Ttext’, ‘-Tdata’, or ‘-Tbss’ options to ld. However, some object file formats, such as a.out, do not store the starting address of the file segments. In those situations, although ld relocates the sections correctly, using ‘objdump -h’ to list the file section headers cannot show the correct addresses. Instead, it shows the usual addresses, which are implicit for the target.

-H

--help

Print a summary of the options to objdump and exit.

-i

--info

Display a list showing all architectures and object formats available for specification with ‘-b’ or ‘-m’.

-j name

--section=name

Display information only for section name.

-l

--line-numbers

Label the display (using debugging information) with the filename and source line numbers corresponding to the object code or relocs shown. Only useful with ‘-d’, ‘-D’, or ‘-r’.

-m machine

--architecture=machine

Specify the architecture to use when disassembling object files. This can be useful when disassembling object files which do not describe architecture information, such as S-records. You can list the available architectures with the ‘-i’ option.

-M options

--disassembler-options=options

Pass target specific information to the disassembler. Only supported on some targets. If it is necessary to specify more than one disassembler option then multiple ‘-M’ options can be used or can be placed together into a comma separated list.

If the target is an ARM architecture then this switch can be used to select which register name set is used during disassembler. Specifying ‘-M reg-names-std’ (the default) will select the register names as used in ARM's instruction set documentation, but with register 13 called 'sp', register 14 called 'lr' and register 15 called 'pc'. Specifying ‘-M reg-names-apcs’ will select the name set used by the ARM Procedure Call Standard, whilst specifying ‘-M reg-names-raw’ will just use ‘r’ followed by the register number.

There are also two variants on the APCS register naming scheme enabled by ‘-M reg-names-atpcs’ and ‘-M reg-names-special-atpcs’ which use the ARM/Thumb Procedure Call Standard naming conventions. (Either with the normal register names or the special register names).

This option can also be used for ARM architectures to force the disassembler to interpret all instructions as Thumb instructions by using the switch ‘--disassembler-options=force-thumb’. This can be useful when attempting to disassemble thumb code produced by other compilers.

For the x86, some of the options duplicate functions of the ‘-m’ switch, but allow finer grained control. Multiple selections from the following may be specified as a comma separated string. ‘x86-64’, ‘i386’ and ‘i8086’ select disassembly for the given architecture. ‘intel’ and ‘att’ select between intel syntax mode and AT&T syntax mode. ‘addr64’, ‘addr32’, ‘addr16’, ‘data32’ and ‘data16’ specify the default address size and operand size. These four options will be overridden if ‘x86-64’, ‘i386’ or ‘i8086’ appear later in the option string. Lastly, ‘suffix’, when in AT&T mode, instructs the disassembler to print a mnemonic suffix even when the suffix could be inferred by the operands.

For PPC, ‘booke’, ‘booke32’ and ‘booke64’ select disassembly of BookE instructions. ‘32’ and ‘64’ select PowerPC and PowerPC64 disassembly, respectively. ‘e300’ selects disassembly for the e300 family. ‘440’ selects disassembly for the PowerPC 440.

For MIPS, this option controls the printing of instruction mnemonic names and register names in disassembled instructions. Multiple selections from the following may be specified as a comma separated string, and invalid options are ignored:

no-aliases

Print the 'raw' instruction mnemonic instead of some pseudo instruction mnemonic. I.e., print 'daddu' or 'or' instead of 'move', 'sll' instead of 'nop', etc.

gpr-names=ABI

Print GPR (general-purpose register) names as appropriate for the specified ABI. By default, GPR names are selected according to the ABI of the binary being disassembled.

fpr-names=ABI

Print FPR (floating-point register) names as appropriate for the specified ABI. By default, FPR numbers are printed rather than names.

cp0-names=ARCH

Print CP0 (system control coprocessor; coprocessor 0) register names as appropriate for the CPU or architecture specified by ARCH. By default, CP0 register names are selected according to the architecture and CPU of the binary being disassembled.

hwr-names=ARCH

Print HWR (hardware register, used by the rdhwr instruction) names as appropriate for the CPU or architecture specified by ARCH. By default, HWR names are selected according to the architecture and CPU of the binary being disassembled.

reg-names=ABI

Print GPR and FPR names as appropriate for the selected ABI.

reg-names=ARCH

Print CPU-specific register names (CP0 register and HWR names) as appropriate for the selected CPU or architecture.

For any of the options listed above, ABI or ARCH may be specified as ‘numeric’ to have numbers printed rather than names, for the selected types of registers. You can list the available values of ABI and ARCH using the ‘--help’ option.

For VAX, you can specify function entry addresses with ‘-M entry:0xf00ba’. You can use this multiple times to properly disassemble VAX binary files that don't contain symbol tables (like ROM dumps). In these cases, the function entry mask would otherwise be decoded as VAX instructions, which would probably lead the rest of the function being wrongly disassembled.

-p

--private-headers

Print information that is specific to the object file format. The exact information printed depends upon the object file format. For some object file formats, no additional information is printed.

-r

--reloc

Print the relocation entries of the file. If used with ‘-d’ or ‘-D’, the relocations are printed interspersed with the disassembly.

-R

--dynamic-reloc

Print the dynamic relocation entries of the file. This is only meaningful for dynamic objects, such as certain types of shared libraries.

-s

--full-contents

Display the full contents of any sections requested. By default all non-empty sections are displayed.

-S

--source

Display source code intermixed with disassembly, if possible. Implies ‘-d’.

--show-raw-insn

When disassembling instructions, print the instruction in hex as well as in symbolic form. This is the default except when ‘--prefix-addresses’ is used.

--no-show-raw-insn

When disassembling instructions, do not print the instruction bytes. This is the default when ‘--prefix-addresses’ is used.

-W

--dwarf

Displays the contents of the DWARF debug sections in the file, if any are present.

-G

--stabs

Display the full contents of any sections requested. Display the contents of the .stab and .stab.index and .stab.excl sections from an ELF file. This is only useful on systems (such as Solaris 2.0) in which .stab debugging symbol-table entries are carried in an ELF section. In most other file formats, debugging symbol-table entries are interleaved with linkage symbols, and are visible in the ‘--syms’ output. For more information on stabs symbols, see Stabs: (stabs.info)Top section `Stabs Overview' in The “stabs” debug format.

--start-address=address

Start displaying data at the specified address. This affects the output of the ‘-d’, ‘-r’ and ‘-s’ options.

--stop-address=address

Stop displaying data at the specified address. This affects the output of the ‘-d’, ‘-r’ and ‘-s’ options.

-t

--syms

Print the symbol table entries of the file. This is similar to the information provided by the ‘nm’ program.

-T

--dynamic-syms

Print the dynamic symbol table entries of the file. This is only meaningful for dynamic objects, such as certain types of shared libraries. This is similar to the information provided by the ‘nm’ program when given the ‘-D’ (‘--dynamic’) option.

--special-syms

When displaying symbols include those which the target considers to be special in some way and which would not normally be of interest to the user.

-V

--version

Print the version number of objdump and exit.

-x

--all-headers

Display all available header information, including the symbol table and relocation entries. Using ‘-x’ is equivalent to specifying all of ‘-a -f -h -p -r -t’.

-w

--wide

Format some lines for output devices that have more than 80 columns. Also do not truncate symbol names when they are displayed.

-z

--disassemble-zeroes

Normally the disassembly output will skip blocks of zeroes. This option directs the disassembler to disassemble those blocks, just like any other data.