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-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: 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

   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.

       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)

1.18.24                           2017-05-17                dpkg-buildflags(1)

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