dpkg-buildflags(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | COMMANDS | SUPPORTED FLAGS | FEATURE AREAS | ENVIRONMENT | FILES | EXAMPLES | COLOPHON

dpkg-buildflags(1)             dpkg suite             dpkg-buildflags(1)

NAME         top

       dpkg-buildflags - returns build flags to use during package build

SYNOPSIS         top

       dpkg-buildflags [option...] [command]

DESCRIPTION         top

       dpkg-buildflags is a tool to retrieve compilation flags to use
       during build of Debian packages.  The default flags are defined
       by the vendor but they can be extended/overridden in several
       ways:

       1.     system-wide with /usr/local/etc/dpkg/buildflags.conf;

       2.     for the current user with
              $XDG_CONFIG_HOME/dpkg/buildflags.conf where
              $XDG_CONFIG_HOME defaults to $HOME/.config;

       3.     temporarily by the user with environment variables (see
              section ENVIRONMENT);

       4.     dynamically by the package maintainer with environment
              variables set via debian/rules (see section ENVIRONMENT).

       The configuration files can contain four types of directives:

       SET flag value
              Override the flag named flag to have the value value.

       STRIP flag value
              Strip from the flag named flag all the build flags listed
              in value.

       APPEND flag value
              Extend the flag named flag by appending the options given
              in value.  A space is prepended to the appended value if
              the flag's current value is non-empty.

       PREPEND flag value
              Extend the flag named flag by prepending the options given
              in value.  A space is appended to the prepended value if
              the flag's current value is non-empty.

       The configuration files can contain comments on lines starting
       with a hash (#). Empty lines are also ignored.

COMMANDS         top

       --dump Print to standard output all compilation flags and their
              values. It prints one flag per line separated from its
              value by an equal sign (“flag=value”). This is the default
              action.

       --list Print the list of flags supported by the current vendor
              (one per line). See the SUPPORTED FLAGS section for more
              information about them.

       --status
              Display any information that can be useful to explain the
              behaviour of dpkg-buildflags (since dpkg 1.16.5): relevant
              environment variables, current vendor, state of all
              feature flags.  Also print the resulting compiler flags
              with their origin.

              This is intended to be run from debian/rules, so that the
              build log keeps a clear trace of the build flags used.
              This can be useful to diagnose problems related to them.

       --export=format
              Print to standard output commands that can be used to
              export all the compilation flags for some particular tool.
              If the format value is not given, sh is assumed. Only
              compilation flags starting with an upper case character
              are included, others are assumed to not be suitable for
              the environment. Supported formats:

              sh     Shell commands to set and export all the
                     compilation flags in the environment. The flag
                     values are quoted so the output is ready for
                     evaluation by a shell.

              cmdline
                     Arguments to pass to a build program's command line
                     to use all the compilation flags (since dpkg
                     1.17.0). The flag values are quoted in shell
                     syntax.

              configure
                     This is a legacy alias for cmdline.

              make   Make directives to set and export all the
                     compilation flags in the environment. Output can be
                     written to a makefile fragment and evaluated using
                     an include directive.

       --get flag
              Print the value of the flag on standard output. Exits with
              0 if the flag is known otherwise exits with 1.

       --origin flag
              Print the origin of the value that is returned by --get.
              Exits with 0 if the flag is known otherwise exits with 1.
              The origin can be one of the following values:

              vendor the original flag set by the vendor is returned;

              system the flag is set/modified by a system-wide
                     configuration;

              user   the flag is set/modified by a user-specific
                     configuration;

              env    the flag is set/modified by an environment-specific
                     configuration.

       --query
              Print any information that can be useful to explain the
              behaviour of the program: current vendor, relevant
              environment variables, feature areas, state of all feature
              flags, and the compiler flags with their origin (since
              dpkg 1.19.0).

              For example:
                Vendor: Debian
                Environment:
                 DEB_CFLAGS_SET=-O0 -Wall

                Area: qa
                Features:
                 bug=no
                 canary=no

                Area: reproducible
                Features:
                 timeless=no

                Flag: CFLAGS
                Value: -O0 -Wall
                Origin: env

                Flag: CPPFLAGS
                Value: -D_FORTIFY_SOURCE=2
                Origin: vendor

       --query-features area
              Print the features enabled for a given area (since dpkg
              1.16.2).  The only currently recognized areas on Debian
              and derivatives are future, qa, reproducible, sanitize and
              hardening, see the FEATURE AREAS section for more details.
              Exits with 0 if the area is known otherwise exits with 1.

              The output is in RFC822 format, with one section per
              feature.  For example:

                Feature: pie
                Enabled: yes

                Feature: stackprotector
                Enabled: yes

       --help Show the usage message and exit.

       --version
              Show the version and exit.

SUPPORTED FLAGS         top

       CFLAGS Options for the C compiler. The default value set by the
              vendor includes -g and the default optimization level (-O2
              usually, or -O0 if the DEB_BUILD_OPTIONS environment
              variable defines noopt).

       CPPFLAGS
              Options for the C preprocessor. Default value: empty.

       CXXFLAGS
              Options for the C++ compiler. Same as CFLAGS.

       OBJCFLAGS
              Options for the Objective C compiler. Same as CFLAGS.

       OBJCXXFLAGS
              Options for the Objective C++ compiler. Same as CXXFLAGS.

       GCJFLAGS
              Options for the GNU Java compiler (gcj). A subset of
              CFLAGS.

       FFLAGS Options for the Fortran 77 compiler. A subset of CFLAGS.

       FCFLAGS
              Options for the Fortran 9x compiler. Same as FFLAGS.

       LDFLAGS
              Options passed to the compiler when linking executables or
              shared objects (if the linker is called directly, then -Wl
              and , have to be stripped from these options). Default
              value: empty.

       New flags might be added in the future if the need arises (for
       example to support other languages).

FEATURE AREAS         top

       Each area feature can be enabled and disabled in the
       DEB_BUILD_OPTIONS and DEB_BUILD_MAINT_OPTIONS environment
       variable's area value with the ‘+’ and ‘-’ modifier.  For
       example, to enable the hardening “pie” feature and disable the
       “fortify” feature you can do this in debian/rules:

         export DEB_BUILD_MAINT_OPTIONS=hardening=+pie,-fortify

       The special feature all (valid in any area) can be used to enable
       or disable all area features at the same time.  Thus disabling
       everything in the hardening area and enabling only “format” and
       “fortify” can be achieved with:

         export DEB_BUILD_MAINT_OPTIONS=hardening=-all,+format,+fortify

   future
       Several compile-time options (detailed below) can be used to
       enable features that should be enabled by default, but cannot due
       to backwards compatibility reasons.

       lfs    This setting (disabled by default) enables Large File
              Support on 32-bit architectures where their ABI does not
              include LFS by default, by adding -D_LARGEFILE_SOURCE
              -D_FILE_OFFSET_BITS=64 to CPPFLAGS.

   qa
       Several compile-time options (detailed below) can be used to help
       detect problems in the source code or build system.

       bug    This setting (disabled by default) adds any warning option
              that reliably detects problematic source code. The
              warnings are fatal.  The only currently supported flags
              are CFLAGS and CXXFLAGS with flags set to
              -Werror=array-bounds, -Werror=clobbered,
              -Werror=implicit-function-declaration and
              -Werror=volatile-register-var.

       canary This setting (disabled by default) adds dummy canary
              options to the build flags, so that the build logs can be
              checked for how the build flags propagate and to allow
              finding any omission of normal build flag settings.  The
              only currently supported flags are CPPFLAGS, CFLAGS,
              OBJCFLAGS, CXXFLAGS and OBJCXXFLAGS with flags set to
              -D__DEB_CANARY_flag_random-id__, and LDFLAGS set to
              -Wl,-z,deb-canary-random-id.

   sanitize
       Several compile-time options (detailed below) can be used to help
       sanitize a resulting binary against memory corruptions, memory
       leaks, use after free, threading data races and undefined
       behavior bugs.  Note: these options should not be used for
       production builds as they can reduce reliability for conformant
       code, reduce security or even functionality.

       address
              This setting (disabled by default) adds -fsanitize=address
              to LDFLAGS and -fsanitize=address -fno-omit-frame-pointer
              to CFLAGS and CXXFLAGS.

       thread This setting (disabled by default) adds -fsanitize=thread
              to CFLAGS, CXXFLAGS and LDFLAGS.

       leak   This setting (disabled by default) adds -fsanitize=leak to
              LDFLAGS. It gets automatically disabled if either the
              address or the thread features are enabled, as they imply
              it.

       undefined
              This setting (disabled by default) adds
              -fsanitize=undefined to CFLAGS, CXXFLAGS and LDFLAGS.

   hardening
       Several compile-time options (detailed below) can be used to help
       harden a resulting binary against memory corruption attacks, or
       provide additional warning messages during compilation.  Except
       as noted below, these are enabled by default for architectures
       that support them.

       format This setting (enabled by default) adds -Wformat
              -Werror=format-security to CFLAGS, CXXFLAGS, OBJCFLAGS and
              OBJCXXFLAGS.  This will warn about improper format string
              uses, and will fail when format functions are used in a
              way that represent possible security problems. At present,
              this warns about calls to printf and scanf functions where
              the format string is not a string literal and there are no
              format arguments, as in printf(foo); instead of
              printf("%s", foo); This may be a security hole if the
              format string came from untrusted input and contains ‘%n’.

       fortify
              This setting (enabled by default) adds -D_FORTIFY_SOURCE=2
              to CPPFLAGS. During code generation the compiler knows a
              great deal of information about buffer sizes (where
              possible), and attempts to replace insecure unlimited
              length buffer function calls with length-limited ones.
              This is especially useful for old, crufty code.
              Additionally, format strings in writable memory that
              contain ‘%n’ are blocked. If an application depends on
              such a format string, it will need to be worked around.

              Note that for this option to have any effect, the source
              must also be compiled with -O1 or higher. If the
              environment variable DEB_BUILD_OPTIONS contains noopt,
              then fortify support will be disabled, due to new warnings
              being issued by glibc 2.16 and later.

       stackprotector
              This setting (enabled by default if stackprotectorstrong
              is not in use) adds -fstack-protector
              --param=ssp-buffer-size=4 to CFLAGS, CXXFLAGS, OBJCFLAGS,
              OBJCXXFLAGS, GCJFLAGS, FFLAGS and FCFLAGS.  This adds
              safety checks against stack overwrites. This renders many
              potential code injection attacks into aborting situations.
              In the best case this turns code injection vulnerabilities
              into denial of service or into non-issues (depending on
              the application).

              This feature requires linking against glibc (or another
              provider of __stack_chk_fail), so needs to be disabled
              when building with -nostdlib or -ffreestanding or similar.

       stackprotectorstrong
              This setting (enabled by default) adds
              -fstack-protector-strong to CFLAGS, CXXFLAGS, OBJCFLAGS,
              OBJCXXFLAGS, GCJFLAGS, FFLAGS and FCFLAGS.  This is a
              stronger variant of stackprotector, but without
              significant performance penalties.

              Disabling stackprotector will also disable this setting.

              This feature has the same requirements as stackprotector,
              and in addition also requires gcc 4.9 and later.

       relro  This setting (enabled by default) adds -Wl,-z,relro to
              LDFLAGS.  During program load, several ELF memory sections
              need to be written to by the linker. This flags the loader
              to turn these sections read-only before turning over
              control to the program. Most notably this prevents GOT
              overwrite attacks. If this option is disabled, bindnow
              will become disabled as well.

       bindnow
              This setting (disabled by default) adds -Wl,-z,now to
              LDFLAGS. During program load, all dynamic symbols are
              resolved, allowing for the entire PLT to be marked read-
              only (due to relro above). The option cannot become
              enabled if relro is not enabled.

       pie    This setting (with no global default since dpkg 1.18.23,
              as it is enabled by default now by gcc on the amd64,
              arm64, armel, armhf, hurd-i386, i386, kfreebsd-amd64,
              kfreebsd-i386, mips, mipsel, mips64el, powerpc, ppc64,
              ppc64el, riscv64, s390x, sparc and sparc64 Debian
              architectures) adds the required options to enable or
              disable PIE via gcc specs files, if needed, depending on
              whether gcc injects on that architecture the flags by
              itself or not.  When the setting is enabled and gcc
              injects the flags, it adds nothing.  When the setting is
              enabled and gcc does not inject the flags, it adds -fPIE
              (via /usr/local/share/dpkg/pie-compiler.specs) to CFLAGS,
              CXXFLAGS, OBJCFLAGS, OBJCXXFLAGS, GCJFLAGS, FFLAGS and
              FCFLAGS, and -fPIE -pie (via /usr/local/share/dpkg/pie-
              link.specs) to LDFLAGS.  When the setting is disabled and
              gcc injects the flags, it adds -fno-PIE (via
              /usr/local/share/dpkg/no-pie-compile.specs) to CFLAGS,
              CXXFLAGS, OBJCFLAGS, OBJCXXFLAGS, GCJFLAGS, FFLAGS and
              FCFLAGS, and -fno-PIE -no-pie (via
              /usr/local/share/dpkg/no-pie-link.specs) to LDFLAGS.

              Position Independent Executable are needed to take
              advantage of Address Space Layout Randomization, supported
              by some kernel versions. While ASLR can already be
              enforced for data areas in the stack and heap (brk and
              mmap), the code areas must be compiled as position-
              independent. Shared libraries already do this (-fPIC), so
              they gain ASLR automatically, but binary .text regions
              need to be build PIE to gain ASLR. When this happens, ROP
              (Return Oriented Programming) attacks are much harder
              since there are no static locations to bounce off of
              during a memory corruption attack.

              PIE is not compatible with -fPIC, so in general care must
              be taken when building shared objects. But because the PIE
              flags emitted get injected via gcc specs files, it should
              always be safe to unconditionally set them regardless of
              the object type being compiled or linked.

              Static libraries can be used by programs or other shared
              libraries.  Depending on the flags used to compile all the
              objects within a static library, these libraries will be
              usable by different sets of objects:

              none   Cannot be linked into a PIE program, nor a shared
                     library.

              -fPIE  Can be linked into any program, but not a shared
                     library (recommended).

              -fPIC  Can be linked into any program and shared library.

              If there is a need to set these flags manually, bypassing
              the gcc specs injection, there are several things to take
              into account. Unconditionally and explicitly passing
              -fPIE, -fpie or -pie to a build-system using libtool is
              safe as these flags will get stripped when building shared
              libraries.  Otherwise on projects that build both programs
              and shared libraries you might need to make sure that when
              building the shared libraries -fPIC is always passed last
              (so that it overrides any previous -PIE) to compilation
              flags such as CFLAGS, and -shared is passed last (so that
              it overrides any previous -pie) to linking flags such as
              LDFLAGS. Note: This should not be needed with the default
              gcc specs machinery.

              Additionally, since PIE is implemented via a general
              register, some register starved architectures (but not
              including i386 anymore since optimizations implemented in
              gcc >= 5) can see performance losses of up to 15% in very
              text-segment-heavy application workloads; most workloads
              see less than 1%. Architectures with more general
              registers (e.g. amd64) do not see as high a worst-case
              penalty.

   reproducible
       The compile-time options detailed below can be used to help
       improve build reproducibility or provide additional warning
       messages during compilation. Except as noted below, these are
       enabled by default for architectures that support them.

       timeless
              This setting (enabled by default) adds -Wdate-time to
              CPPFLAGS.  This will cause warnings when the __TIME__,
              __DATE__ and __TIMESTAMP__ macros are used.

       fixfilepath
              This setting (disabled by default) adds
              -ffile-prefix-map=BUILDPATH=.  to CFLAGS, CXXFLAGS,
              OBJCFLAGS, OBJCXXFLAGS, GCJFLAGS, FFLAGS and FCFLAGS where
              BUILDPATH is set to the top-level directory of the package
              being built.  This has the effect of removing the build
              path from any generated file.

              If both fixdebugpath and fixfilepath are set, this option
              takes precedence, because it is a superset of the former.

       fixdebugpath
              This setting (enabled by default) adds
              -fdebug-prefix-map=BUILDPATH=.  to CFLAGS, CXXFLAGS,
              OBJCFLAGS, OBJCXXFLAGS, GCJFLAGS, FFLAGS and FCFLAGS where
              BUILDPATH is set to the top-level directory of the package
              being built.  This has the effect of removing the build
              path from any generated debug symbols.

ENVIRONMENT         top

       There are 2 sets of environment variables doing the same
       operations, the first one (DEB_flag_op) should never be used
       within debian/rules. It's meant for any user that wants to
       rebuild the source package with different build flags. The second
       set (DEB_flag_MAINT_op) should only be used in debian/rules by
       package maintainers to change the resulting build flags.

       DEB_flag_SET
       DEB_flag_MAINT_SET
              This variable can be used to force the value returned for
              the given flag.

       DEB_flag_STRIP
       DEB_flag_MAINT_STRIP
              This variable can be used to provide a space separated
              list of options that will be stripped from the set of
              flags returned for the given flag.

       DEB_flag_APPEND
       DEB_flag_MAINT_APPEND
              This variable can be used to append supplementary options
              to the value returned for the given flag.

       DEB_flag_PREPEND
       DEB_flag_MAINT_PREPEND
              This variable can be used to prepend supplementary options
              to the value returned for the given flag.

       DEB_BUILD_OPTIONS
       DEB_BUILD_MAINT_OPTIONS
              These variables can be used by a user or maintainer to
              disable/enable various area features that affect build
              flags.  The DEB_BUILD_MAINT_OPTIONS variable overrides any
              setting in the DEB_BUILD_OPTIONS feature areas.  See the
              FEATURE AREAS section for details.

       DEB_VENDOR
              This setting defines the current vendor.  If not set, it
              will discover the current vendor by reading
              /usr/local/etc/dpkg/origins/default.

       DEB_BUILD_PATH
              This variable sets the build path (since dpkg 1.18.8) to
              use in features such as fixdebugpath so that they can be
              controlled by the caller.  This variable is currently
              Debian and derivatives-specific.

       DPKG_COLORS
              Sets the color mode (since dpkg 1.18.5).  The currently
              accepted values are: auto (default), always and never.

       DPKG_NLS
              If set, it will be used to decide whether to activate
              Native Language Support, also known as
              internationalization (or i18n) support (since dpkg
              1.19.0).  The accepted values are: 0 and 1 (default).

FILES         top

   Configuration files
       /usr/local/etc/dpkg/buildflags.conf
              System wide configuration file.

       $XDG_CONFIG_HOME/dpkg/buildflags.conf or
       $HOME/.config/dpkg/buildflags.conf
              User configuration file.

   Packaging support
       /usr/local/share/dpkg/buildflags.mk
              Makefile snippet that will load (and optionally export)
              all flags supported by dpkg-buildflags into variables
              (since dpkg 1.16.1).

EXAMPLES         top

       To pass build flags to a build command in a makefile:

           $(MAKE) $(shell dpkg-buildflags --export=cmdline)

           ./configure $(shell dpkg-buildflags --export=cmdline)

       To set build flags in a shell script or shell fragment, eval can
       be used to interpret the output and to export the flags in the
       environment:

           eval "$(dpkg-buildflags --export=sh)" && make

       or to set the positional parameters to pass to a command:

           eval "set -- $(dpkg-buildflags --export=cmdline)"
           for dir in a b c; do (cd $dir && ./configure "$@" && make); done

   Usage in debian/rules
       You should call dpkg-buildflags or include buildflags.mk from the
       debian/rules file to obtain the needed build flags to pass to the
       build system.  Note that older versions of dpkg-buildpackage
       (before dpkg 1.16.1) exported these flags automatically. However,
       you should not rely on this, since this breaks manual invocation
       of debian/rules.

       For packages with autoconf-like build systems, you can pass the
       relevant options to configure or make(1) directly, as shown
       above.

       For other build systems, or when you need more fine-grained
       control about which flags are passed where, you can use --get. Or
       you can include buildflags.mk instead, which takes care of
       calling dpkg-buildflags and storing the build flags in make
       variables.

       If you want to export all buildflags into the environment (where
       they can be picked up by your build system):

           DPKG_EXPORT_BUILDFLAGS = 1
           include /usr/local/share/dpkg/buildflags.mk

       For some extra control over what is exported, you can manually
       export the variables (as none are exported by default):

           include /usr/local/share/dpkg/buildflags.mk
           export CPPFLAGS CFLAGS LDFLAGS

       And you can of course pass the flags to commands manually:

           include /usr/local/share/dpkg/buildflags.mk
           build-arch:
                $(CC) -o hello hello.c $(CPPFLAGS) $(CFLAGS) $(LDFLAGS)

COLOPHON         top

       This page is part of the dpkg (Debian Package Manager) project.
       Information about the project can be found at 
       ⟨https://wiki.debian.org/Teams/Dpkg/⟩.  If you have a bug report
       for this manual page, see
       ⟨http://bugs.debian.org/cgi-bin/pkgreport.cgi?src=dpkg⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨https://salsa.debian.org/dpkg-team/dpkg.git⟩ on 2021-06-20.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2021-06-17.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

1.19.6-2-g6e42d5               2019-03-25             dpkg-buildflags(1)

Pages that refer to this page: dpkg-buildpackage(1)deb-src-rules(5)debhelper(7)