dpkg-buildflags(1)



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/overridden 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 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
       --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
       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"
       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 default since dpkg 1.18.23,  and  injected
              by  default  by  gcc  on  the  amd64, arm64, armel, armhf, i386,
              kfreebsd-amd64, kfreebsd-i386, mips, mipsel, mips64el,  ppc64el,
              s390x, sparc and sparc64 Debian architectures) adds the required
              options via gcc specs files if needed to enable or disable  PIE.
              When enabled and injected by gcc, adds nothing. When enabled and
              not injected by gcc, adds -fPIE to CFLAGS, CXXFLAGS,  OBJCFLAGS,
              OBJCXXFLAGS,  GCJFLAGS,  FFLAGS  and  FCFLAGS, and -fPIE -pie to
              LDFLAGS. When disabled and injected by  gcc,  adds  -fno-PIE  to
              CFLAGS,  CXXFLAGS,  OBJCFLAGS, OBJCXXFLAGS, GCJFLAGS, FFLAGS and
              FCFLAGS, and -fno-PIE -no-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 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.

       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
       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
              /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.

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).

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
       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/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)

1.19.0.4                          2017-10-22                dpkg-buildflags(1)

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