dwz(1) General Commands Manual dwz(1)
NAME
dwz - DWARF optimization and duplicate removal tool
SYNOPSIS
dwz [OPTION...] [FILES]
DESCRIPTION
dwz is a program that attempts to optimize DWARF debugging information
contained in ELF shared libraries and ELF executables for size, by re-
placing DWARF information representation with equivalent smaller repre-
sentation where possible and by reducing the amount of duplication us-
ing techniques from DWARF standard appendix E - creating DW_TAG_par-
tial_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, 4, most of version 5 and GNU extensions on top of those. It is
strongly recommended to use at least DWARF 3, but using DWARF 4 or
higher will work much better.
While most of DWARF 5 is supported dwz doesn't yet generate spec com-
pliant DWARF Supplementary Object Files (DWARF 5, section 7.3.6) unless
the --dwarf-5 option is used. Instead of a .debug_sup section it will
generate by default a .gnu_debugaltlink section. And it will use the
DW_FORM_GNU_strp_alt and DW_FORM_GNU_reg_alt, instead of
DW_FORM_strp_sup and DW_FORM_ref_sup to keep compatibility with exist-
ing DWARF consumers.
DWARF 4 .debug_types are supported, but DWARF 5 DW_UT_type units are
not. Likewise .gdb_index is supported, but the DWARF 5 .debug_names is
not. Also some forms and sections that are only emitted by GCC when
generating Split DWARF, DW_FORM_strx and .debug_str_offsets,
DW_FORM_addrx and .debug_addr, DW_FORM_rnglistx and DW_FORM_loclistsx,
are not supported yet.
The tool has two main modes of operation, without the -m option it at-
tempts to optimize DWARF debugging information in each given object
(executable or shared library) individually, with the -m option it af-
terwards attempts to optimize even more by moving DWARF debugging in-
formation entries (DIEs), strings and macro descriptions duplicated in
more than one object into a newly created ELF ET_REL object whose file-
name is given as -m option argument. The debug sections in the exe-
cutables and shared libraries specified on the command line are then
modified again, referring to the entities in the newly created object.
OPTIONS
-m FILE --multifile FILE
Multifile mode. After processing all named executables and
shared libraries, attempt to create ELF object FILE and put de-
bugging 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 de-
fault 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|none> --low-mem-die-limit <COUNT|none>
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 at-
tempt 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). Specifying none as argument disables the
limit.
-L <COUNT|none> --max-die-limit <COUNT|none>
Don't attempt to optimize executables or shared libraries con-
taining more than COUNT DIEs at all. The default is 50 million
DIEs. Specifying none as argument disables the limit.
-5 --dwarf-5
Emit standard DWARF 5 Supplementary Object Files with .debug_sup
and corresponding forms, instead of the GNU extension .gnu_de-
bugaltlink and corresponding forms.
--odr / --no-odr
Experimental. Enable/disable One-Definition-Rule optimization
for C++ compilation units. This optimization causes
struct/union/class DIEs with the same name to be considered
equal. This has the effect that DIEs referring to distinct DIEs
representing the same type (like f.i. pointer type DIEs) are
considered equal, and may be deduplicated. The status of this
optimization is experimental. It's disabled in low-mem mode.
Disabled by default.
--odr-mode=<basic|link>
Set the One-Definition-Rule optimization aggressiveness: basic
or link. When using the link setting, the optimization will at-
tempt to replace declarations of a struct/union/class with a
corresponding definition. When using the basic setting, that
part of the optimization is disabled. In normal operation, the
link setting should be used. The basic setting is provided only
as fallback in case of problems with the link setting. Set to
link by default.
--import-optimize / --no-import-optimize
Enable/disable optimization that reduces the number of
DW_TAG_imported_unit DIEs generated to import the partial units
created by dwz. Disabling the optimization can be used to work
around problems in the optimization, or to make it easier to ob-
serve which CU imports which PU. Enabled by default.
-? --help
Print short help and exit.
-v --version
Print version number and short licensing notice and exit.
ARGUMENTS
Command-line arguments should be the executables, shared libraries or
their stripped to file separate debug information objects.
EXAMPLES
$ 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/foo-
bar-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 de-
bugging information if successful into foo.dwz file it creates.
$ dwz *.debug foo/*.debug
will attempt to optimize debugging information in *.debug and foo/*.de-
bug files, optimizing each file individually in place.
$ dwz
is equivalent to dwz a.out command.
SEE ALSO
http://dwarfstd.org/doc/DWARF4.pdf , http://dwarfstd.org/doc/DWARF5.pdf
, gdb(1).
AUTHORS
Jakub Jelinek <jakub@redhat.com>, Tom de Vries <tdevries@suse.de>, Mark
Wielaard <mark@klomp.org>
BUGS
Use the Bugzilla link of the project web page or our mailing list.
https://sourceware.org/dwz/, <dwz@sourceware.org>.
15 Feb 2021 dwz(1)
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