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: 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 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. The only  currently
              recognized  areas  are  qa,  reproducible 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

   Quality Assurance (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.

   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.

   Reproducibility
       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 (disabled by default) adds -Wdate-time to CPPFLAGS.
              This will cause warnings when the __TIME__, __DATE__ and __TIME-
              STAMP__ 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/build-
       flags.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).

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-build-
       flags 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)
