dpkg-buildflags [option...] [command]
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
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
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.
--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
Print to standard output shell (if format is sh) or make (if
format is make) commands that can be used to export all the com-
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-
env the flag is set/modified by an environment-specific con-
--help Show the usage message and exit.
Show the version and exit.
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
Options for the C preprocessor. Default value: empty.
Options for the C++ compiler. Same as CFLAGS.
FFLAGS Options for the Fortran compiler. Same as CFLAGS.
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.
System wide configuration file.
$XDG_CONFIG_HOME/dpkg/buildflags.conf or $HOME/.config/dpkg/build-
User configuration file.
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
This variable can be used to append supplementary options to the
value returned for the given flag.
This variable can be used to prepend supplementary options to
the value returned for the given flag.
This variable can be used to disable/enable various hardening
build flags through the hardening option. See the HARDENING sec-
tion for details.
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.
Each hardening feature can be enabled and disabled in the
DEB_BUILD_MAINT_OPTIONS environment variable's hardening value with the
"+" and "-" modifier. For example, to enable the "pie" feature and dis-
able the "fortify" feature you can do this in debian/rules:
The special feature all can be used to enable or disable all hardening
features at the same time. Thus disabling everything and enabling only
"format" and "fortify" can be achieved with:
format This setting (enabled by default) adds -Wformat -Wformat-secu-
rity -Werror=format-security to CFLAGS and CXXFLAGS. This will
warn about improper format string uses, and will fail when for-
mat functions are used in a way that 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".
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.
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.
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).
pie This setting (disabled by default) adds -fPIE to CFLAGS and
CXXFLAGS, and -fPIE -pie to LDFLAGS. Position Independent Exe-
cutable 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-indepen-
dent. 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 Pro-
gramming) 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
Copyright (C) 2010-2011 Raphael Hertzog
Copyright (C) 2011 Kees Cook
This is free software; see the GNU General Public Licence version 2 or
later for copying conditions. There is NO WARRANTY.
Debian Project 2011-09-13 dpkg-buildflags(1)
Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2017
All Rights Reserved.