Provided by: dpkg-dev_1.18.4ubuntu1_all bug

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  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: 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” 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.

       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  (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 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.

              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  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.

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.

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 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)