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Section: GNU Development Tools (1)
Updated: 2017-09-21


objdump - display information from object files. 


objdump [-a|--archive-headers]
        [-b bfdname|--target=bfdname]
        [-C|--demangle[=style] ]
        [-EB|-EL|--endian={big | little }]
        [-j section|--section=section]
        [-m machine|--architecture=machine]
        [-M options|--disassembler-options=options]


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

objfile... are the object files to be examined. When youspecify archives, objdump shows information on each of the memberobject files. 


The long and short forms of options, shown here as alternatives, areequivalent. 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.
If any of the objfile files are archives, display the archiveheader information (in a format similar to ls -l). Besides theinformation you could list with ar tv, objdump -a showsthe object file format of each archive member.
When dumping information, first add offset to all the sectionaddresses. This is useful if the section addresses do not correspond tothe symbol table, which can happen when putting sections at particularaddresses when using a format which can not represent section addresses,such as a.out.
-b bfdname
Specify that the object-code format for the object files isbfdname. This option may not be necessary; objdump canautomatically recognize many formats.

For example,

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

displays summary information from the section headers (-h) offu.o, which is explicitly identified (-m) as a VAX objectfile in the format produced by Oasys compilers. You can list theformats available with the -i option.

Decode (demangle) low-level symbol names into user-level names.Besides removing any initial underscore prepended by the system, thismakes C++ function names readable. Different compilers have differentmangling styles. The optional demangling style argument can be used tochoose an appropriate demangling style for your compiler.
Display debugging information. This attempts to parse STABS and IEEEdebugging format information stored in the file and print it out usinga C like syntax. If neither of these formats are found this optionfalls back on the -W option to print any DWARF information inthe file.
Like -g, but the information is generated in a format compatiblewith ctags tool.
Display the assembler mnemonics for the machine instructions fromobjfile. This option only disassembles those sections which areexpected to contain instructions.
Like -d, but disassemble the contents of all sections, not justthose expected to contain instructions.

If the target is an ARM architecture this switch also has the effectof forcing the disassembler to decode pieces of data found in codesections as if they were instructions.

When disassembling, print the complete address on each line. This isthe older disassembly format.
Specify the endianness of the object files. This only affectsdisassembly. This can be useful when disassembling a file format whichdoes not describe endianness information, such as S-records.
Display summary information from the overall header ofeach of the objfile files.
When disassembling sections, whenever a symbol is displayed, alsodisplay the file offset of the region of data that is about to bedumped. If zeroes are being skipped, then when disassembly resumes,tell the user how many zeroes were skipped and the file offset of thelocation from where the disassembly resumes. When dumping sections,display the file offset of the location from where the dump starts.
Specify that when displaying interlisted source code/disassembly(assumes -S) from a file that has not yet been displayed, extend thecontext to the start of the file.
Display summary information from the section headers of theobject file.

File segments may be relocated to nonstandard addresses, for example byusing the -Ttext, -Tdata, or -Tbss options told. However, some object file formats, such as a.out, do notstore 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 thetarget.

Print a summary of the options to objdump and exit.
Display a list showing all architectures and object formats availablefor specification with -b or -m.
-j name
Display information only for section name.
Label the display (using debugging information) with the filename andsource line numbers corresponding to the object code or relocs shown.Only useful with -d, -D, or -r.
-m machine
Specify the architecture to use when disassembling object files. Thiscan be useful when disassembling object files which do not describearchitecture information, such as S-records. You can list the availablearchitectures with the -i option.

If the target is an ARM architecture then this switch has anadditional effect. It restricts the disassembly to only thoseinstructions supported by the architecture specified by machine.If it is necessary to use this switch because the input file does notcontain any architecture information, but it is also desired todisassemble all the instructions use -marm.

-M options
Pass target specific information to the disassembler. Only supported onsome targets. If it is necessary to specify more than onedisassembler option then multiple -M options can be used orcan be placed together into a comma separated list.

If the target is an ARM architecture then this switch can be used toselect which register name set is used during disassembler. Specifying-M reg-names-std (the default) will select the register names asused 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 ARMProcedure Call Standard, whilst specifying -M reg-names-raw willjust use r followed by the register number.

There are also two variants on the APCS register naming scheme enabledby -M reg-names-atpcs and -M reg-names-special-atpcs whichuse the ARM/Thumb Procedure Call Standard naming conventions. (Eitherwith the normal register names or the special register names).

This option can also be used for ARM architectures to force thedisassembler to interpret all instructions as Thumb instructions byusing the switch --disassembler-options=force-thumb. This can beuseful when attempting to disassemble thumb code produced by othercompilers.

For the x86, some of the options duplicate functions of the -mswitch, but allow finer grained control. Multiple selections from thefollowing may be specified as a comma separated string.x86-64, i386 and i8086 select disassembly forthe given architecture. intel and att select betweenintel syntax mode and AT&T syntax and att-mnemonic select betweenintel mnemonic mode and AT&T mnemonic mode. intel-mnemonicimplies intel and att-mnemonic implies att.addr64, addr32,addr16, data32 and data16 specify the defaultaddress size and operand size. These four options will be overridden ifx86-64, i386 or i8086 appear later in theoption string. Lastly, suffix, when in AT&T mode,instructs the disassembler to print a mnemonic suffix even when thesuffix could be inferred by the operands.

For PowerPC, booke controls the disassembly of BookEinstructions. 32 and 64 select PowerPC andPowerPC64 disassembly, respectively. e300 selectsdisassembly for the e300 family. 440 selects disassembly forthe PowerPC 440. ppcps selects disassembly for the pairedsingle instructions of the PPC750CL.

For MIPS, this option controls the printing of instruction mnemonicnames and register names in disassembled instructions. Multipleselections from the following may be specified as a comma separatedstring, and invalid options are ignored:

Print the 'raw' instruction mnemonic instead of some pseudoinstruction mnemonic. I.e., print 'daddu' or 'or' instead of 'move','sll' instead of 'nop', etc.
Print GPR (general-purpose register) names as appropriatefor the specified ABI. By default, GPR names are selected according tothe ABI of the binary being disassembled.
Print FPR (floating-point register) names asappropriate for the specified ABI. By default, FPR numbers are printedrather than names.
Print CP0 (system control coprocessor; coprocessor 0) register namesas appropriate for the CPU or architecture specified byARCH. By default, CP0 register names are selected according tothe architecture and CPU of the binary being disassembled.
Print HWR (hardware register, used by the "rdhwr" instruction) namesas appropriate for the CPU or architecture specified byARCH. By default, HWR names are selected according tothe architecture and CPU of the binary being disassembled.
Print GPR and FPR names as appropriate for the selected ABI.
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 orARCH may be specified as numeric to have numbers printedrather than names, for the selected types of registers.You can list the available values of ABI and ARCH usingthe --help option.

For VAX, you can specify function entry addresses with -Mentry:0xf00ba. You can use this multiple times to properlydisassemble VAX binary files that don't contain symbol tables (likeROM dumps). In these cases, the function entry mask would otherwisebe decoded as VAX instructions, which would probably lead the restof the function being wrongly disassembled.

Print information that is specific to the object file format. The exactinformation printed depends upon the object file format. For someobject file formats, no additional information is printed.
Print the relocation entries of the file. If used with -d or-D, the relocations are printed interspersed with thedisassembly.
Print the dynamic relocation entries of the file. This is onlymeaningful for dynamic objects, such as certain types of sharedlibraries. As for -r, if used with -d or-D, the relocations are printed interspersed with thedisassembly.
Display the full contents of any sections requested. By default allnon-empty sections are displayed.
Display source code intermixed with disassembly, if possible. Implies-d.
Specify prefix to add to the absolute paths when used with-S.
Indicate how many initial directory names to strip off the hardwiredabsolute paths. It has no effect without --prefix=prefix.
When disassembling instructions, print the instruction in hex as well asin symbolic form. This is the default except when--prefix-addresses is used.
When disassembling instructions, do not print the instruction bytes.This is the default when --prefix-addresses is used.
Display width bytes on a single line when disassemblinginstructions.
Displays the contents of the debug sections in the file, if any arepresent. If one of the optional letters or words follows the switchthen only data found in those specific sections will be dumped.

Note that there is no single letter option to display the content oftrace sections or .gdb_index.

Display the full contents of any sections requested. Display thecontents of the .stab and .stab.index and .stab.excl sections from anELF file. This is only useful on systems (such as Solaris 2.0) in which".stab" debugging symbol-table entries are carried in an ELFsection. In most other file formats, debugging symbol-table entries areinterleaved with linkage symbols, and are visible in the --symsoutput.
Start displaying data at the specified address. This affects the outputof the -d, -r and -s options.
Stop displaying data at the specified address. This affects the outputof the -d, -r and -s options.
Print the symbol table entries of the file.This is similar to the information provided by the nm program,although the display format is different. The format of the outputdepends upon the format of the file being dumped, but there are two maintypes. One looks like this:

        [  4](sec  3)(fl 0x00)(ty   0)(scl   3) (nx 1) 0x00000000 .bss        [  6](sec  1)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x00000000 fred

where the number inside the square brackets is the number of the entryin the symbol table, the sec number is the section number, thefl value are the symbol's flag bits, the ty number is thesymbol's type, the scl number is the symbol's storage class andthe nx value is the number of auxilary entries associated withthe symbol. The last two fields are the symbol's value and its name.

The other common output format, usually seen with ELF based files,looks like this:

        00000000 l    d  .bss   00000000 .bss        00000000 g       .text  00000000 fred

Here the first number is the symbol's value (sometimes refered to asits address). The next field is actually a set of characters andspaces indicating the flag bits that are set on the symbol. Thesecharacters are described below. Next is the section with which thesymbol is associated or *ABS* if the section is absolute (ienot connected with any section), or *UND* if the section isreferenced in the file being dumped, but not defined there.

After the section name comes another field, a number, which for commonsymbols is the alignment and for other symbol is the size. Finallythe symbol's name is displayed.

The flag characters are divided into 7 groups as follows:

The symbol is a local (l), global (g), unique global (u), neitherglobal nor local (a space) or both global and local (!). Asymbol can be neither local or global for a variety of reasons, e.g.,because it is used for debugging, but it is probably an indication ofa bug if it is ever both local and global. Unique global symbols area GNU extension to the standard set of ELF symbol bindings. For sucha symbol the dynamic linker will make sure that in the entire processthere is just one symbol with this name and type in use.
The symbol is weak (w) or strong (a space).
The symbol denotes a constructor (C) or an ordinary symbol (a space).
The symbol is a warning (W) or a normal symbol (a space). A warningsymbol's name is a message to be displayed if the symbol following thewarning symbol is ever referenced.
The symbol is an indirect reference to another symbol (I), a functionto be evaluated during reloc processing (i) or a normal symbol (aspace).
The symbol is a debugging symbol (d) or a dynamic symbol (D) or anormal symbol (a space).
The symbol is the name of a function (F) or a file (f) or an object(O) or just a normal symbol (a space).
Print the dynamic symbol table entries of the file. This is onlymeaningful for dynamic objects, such as certain types of sharedlibraries. This is similar to the information provided by the nmprogram when given the -D (--dynamic) option.
When displaying symbols include those which the target considers to bespecial in some way and which would not normally be of interest to theuser.
Print the version number of objdump and exit.
Display all available header information, including the symbol table andrelocation entries. Using -x is equivalent to specifying all of-a -f -h -p -r -t.
Format some lines for output devices that have more than 80 columns.Also do not truncate symbol names when they are displayed.
Normally the disassembly output will skip blocks of zeroes. Thisoption directs the disassembler to disassemble those blocks, just likeany other data.
Read command-line options from file. The options read areinserted in place of the original @file option. If filedoes not exist, or cannot be read, then the option will be treatedliterally, and not removed.

Options in file are separated by whitespace. A whitespacecharacter may be included in an option by surrounding the entireoption in either single or double quotes. Any character (including abackslash) may be included by prefixing the character to be includedwith a backslash. The file may itself contain additional@file options; any such options will be processed recursively.



nm(1), readelf(1), and the Info entries for binutils. 


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Permission is granted to copy, distribute and/or modify this documentunder the terms of the GNU Free Documentation License, Version 1.3or any later version published by the Free Software Foundation;with no Invariant Sections, with no Front-Cover Texts, and with noBack-Cover Texts. A copy of the license is included in thesection entitled ``GNU Free Documentation License''.




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