Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see https://wiki.gentoo.org/wiki/Project:Quality_Assurance/Backtraces

Packages describing “debug” as local USE flag

Package “debug” Flag Description
app-cdr/dvdisaster Enable memory debugging.
net-vpn/ovpn-dco Enable debug output in dmesg
dev-lang/spidermonkey Enable assertions to allow for easier debugging of programs that link to spidermonkey -- note this will often crash software on regular end-user systems
app-editors/nano Enable debug messages and assert warnings. Note that these will all be sent straight to stderr rather than some logging facility.
www-client/chromium Enable DCHECK feature with severity configurable at runtime. Mostly intended for debugging and development, NOT RECOMMENDED for general use.
sys-process/fcron Enable debug code and output. Since version 3.0.5 this will no longer force foreground execution, and fcron will be able to run as a service properly.
sys-block/parted Enable debugging as encouraged by upstream: [The default configuration] includes --enable-debug (by default), which contains many assertions. Obviously, these "waste" space, but in the past, they have caught potentially dangerous bugs before they would have done damage, so we think it's worth it. Also, it means we get more bug reports ;)
dev-util/google-perftools Build a set of libraries with debug support (so-called debugalloc). These are available by default but are not needed unless you're actually developing using tcmalloc.
games-action/dxx-rebirth Enable various debugging code paths and sanity checks, not just output. Some of these checks date back to the retail build, and choke on some custom levels because the game was never coded to sufficiently distrust inputs
net-mail/vchkuser Enables debug messages to syslog
sys-auth/pam_u2f Enable debug messages using the pam logging macros.
net-wireless/spectools Build the raw output client for spectools. (for developers)
app-emulation/ski enable extra binary emulation debugging via sys-libs/binutils-libs
dev-lang/crystal Build each module as a separate object file. Speeds build up.
app-arch/innoextract Enable debug logging and the --debug command-line option
net-misc/chrony Get DEBUG_LOG output from chronyd when passing -dd parameter
net-vpn/wireguard-modules Enable verbose debug reporting in dmesg of various WireGuard peer and device information.
app-i18n/librime Enable debugging (including logging of input of RIME input methods)
x11-wm/e16 Build libtrip debugging library
app-portage/eix Build with upstream's CXXFLAGS/LDFLAGS for debugging support; not recommended for normal use.
media-tv/mythtv Instructs Qt to use the 'debug' target
app-misc/rlwrap Enable debug
dev-libs/openct Add debug output to the driver library for pcsc-lite.
x11-misc/albert Enable debugging informations
sys-libs/glibc When USE=hardened, allow fortify/stack violations to dump core (SIGABRT) and not kill self (SIGKILL)
dev-haskell/text-short Enable runtime-checks via 'assert'
net-p2p/transmission Enable assertions
dev-perl/perl-headers Add source locations in generated .ph files to assist with debugging when errors occur
dev-libs/boost Build and install only the debug version of the Boost libraries. Only enable this flag if you're developing against boost.
dev-haskell/atomic-primops Enable extra internal checks.
sys-auth/pambase Enable debug information logging on syslog(3) for all the modules supporting this in the system authentication and system login stacks.
www-servers/monkeyd Enable lots of debugging info
dev-tcltk/expect-lite pull in packages needed for runtime interactive debugger
dev-libs/libevent Support for running in debug mode
net-misc/ptpd Enable debugging informations
sys-devel/gcc Enables GCC's 'checking' facility via --enable-checking=yes,extra,rtl. This adds checks to various compiler passes for integrity and input validation. This can help catch possible miscompilations early as well as latent bugs which could become real problems in future, but at the cost of slower compile times when using GCC. Unrelated to backtraces.

All packages providing a “debug” USE flag (1687)