dpkg-buildflags

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

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

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

DESCRIPTION
       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/overriden in several ways:

       1.     system-wide with /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 two 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
       --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 behav-
              iour  of  dpkg-buildflags (since dpkg 1.16.5): relevant environ-
              ment 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 start-
              ing with an  upper  case  character  are  included,  others  are
              assumed  to  not be suitable for the environment. Supported for-
              mats:

              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  direc-
                     tive.

       --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  configura-
                     tion;

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

       --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 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: no

                Feature: stackprotector
                Enabled: yes

       --help Show the usage message and exit.

       --version
              Show the version and exit.

SUPPORTED FLAGS
       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
       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" fea-
       ture 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

   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.

       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 sani-
       tize  a  resulting binary against memory corruptions, memory leaks, use
       after free, threading data races and undefined behavior bugs.

       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=for-
              mat-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 lit-
              eral  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 con-
              tain  '%n' are blocked. If an application depends on such a for-
              mat 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 sit-
              uations. In the best case this turns code injection vulnerabili-
              ties 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  (disabled  by  default)  adds  -fPIE  to  CFLAGS,
              CXXFLAGS, OBJCFLAGS, OBJCXXFLAGS, GCJFLAGS, FFLAGS and  FCFLAGS,
              and  -fPIE  -pie 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  automati-
              cally,  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.

              This is not compatible with -fPIC so care  must  be  taken  when
              building shared objects.

              Additionally,  since  PIE is implemented via a general register,
              some architectures  (most  notably  i386)  can  see  performance
              losses of up to 15% in very text-segment-heavy application work-
              loads; 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.

ENVIRONMENT
       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 dis-
              able/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.

FILES
   Configuration files
       /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/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).

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

EXAMPLES
       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  environ-
       ment:

           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 rele-
       vant 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/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/share/dpkg/buildflags.mk
           export CPPFLAGS CFLAGS LDFLAGS

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

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

Debian Project                    2014-09-04                dpkg-buildflags(1)
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