dwz man page

dwz — DWARF optimization and duplicate removal tool


dwz [OPTION...] [FILES]


dwz is a program that attempts to optimize DWARF debugging information contained in ELF shared libraries and ELF executables for size, by replacing DWARF information representation with equivalent smaller representation where possible and by reducing the amount of duplication using techniques from DWARF standard appendix E - creating DW_TAG_partial_unit compilation units (CUs) for duplicated information and using DW_TAG_imported_unit to import it into each CU that needs it.

The tool handles DWARF 32-bit format debugging sections of versions 2, 3 and 4 and GNU extensions on top of those, though using DWARF 4 or worst case DWARF 3 is strongly recommended.

The tool has two main modes of operation, without the -m option it attempts to optimize DWARF debugging information in each given object (executable or shared library) individually, with the -m option it afterwards attempts to optimize even more by moving DWARF debugging information entries (DIEs), strings and macro descriptions duplicated in more than one object into a newly created ELF ET_REL object whose filename is given as -m option argument.  The debug sections in the executables and shared libraries specified on the command line are then modified again, referring to the entities in the newly created object.


-m FILE --multifile FILE

Multifile mode. After processing all named executables and shared libraries, attempt to create ELF object FILE and put debugging information duplicated in more than one object there, afterwards optimize each named executable or shared library even further if possible.

-h --hardlink

Look for executables or shared libraries hardlinked together, instead of rewriting them individually rewrite just one of them and hardlink the rest to the first one again.

-M NAME --multifile-name NAME

Specify the name of the common file that should be put into the .gnu_debugaltlink section alongside with its build ID.  By default dwz puts there the argument of the -m option.

-r --relative

Specify that the name of the common file to be put into the .gnu_debugaltlink section is supposed to be relative path from the directory containing the executable or shared library to the file named in the argument of the -m option.  Either -M or -r option can be specified, but not both.

-q --quiet

Silence up some of the most common messages.

-o FILE --output FILE

This option instructs dwz not to overwrite the specified file, but instead store the new content into FILE.  Nothing is written if dwz exits with non-zero exit code.  Can be used only with a single executable or shared library (if there are no arguments at all, a.out is assumed).

-l COUNT --low-mem-die-limit COUNT

Handle executables or shared libraries containing more than COUNT debugging information entries in their .debug_info section using a slower and more memory usage friendly mode and don't attempt to optimize that object in multifile mode. The default is 10 million DIEs.  There is a risk that for very large amounts of debugging information in a single shared library or executable there might not be enough memory (especially when dwz tool is 32-bit binary, it might run out of available virtual address space even sooner).

-L COUNT --max-die-limit COUNT

Don't attempt to optimize executables or shared libraries containing more than COUNT DIEs at all.  The default is 50 million DIEs.

-? --help

Print short help and exit.

-v --version

Print version number and short licensing notice and exit.


Command-line arguments should be the executables, shared libraries or their stripped to file separate debug information objects.


$ dwz -m .dwz/foobar-1.2.debug -rh \
 bin/foo.debug bin/foo2.debug foo/lib/libbar.so.debug

will attempt to optimize debugging information in bin/foo.debug, bin/foo2.debug and lib/libbar.so.debug (by modifying the files in place) and when beneficial also will create .dwz/foobar-1.2.debug file. .gnu_debugaltlink section in the first two files will refer to ../.dwz/foobar-1.2.debug and in the last file to ../../.dwz/foobar-1.2.debug.  If e.g. bin/foo.debug and bin/foo2.debug were hardlinked together initially, they will be hardlinked again and for multifile optimizations considered just as a single file rather than two.

$ dwz -o foo.dwz foo

will not modify foo but instead store the ELF object with optimized debugging information if successful into foo.dwz file it creates.

$ dwz *.debug foo/*.debug

will attempt to optimize debugging information in *.debug and foo/*.debug files, optimizing each file individually in place.

$ dwz

is equivalent to dwz a.out command.

See Also

http://dwarfstd.org/doc/DWARF4.pdf , gdb(1).


Jakub Jelinek <jakub@redhat.com>.


15 June 2012