dpkg-buildflags(1)

dpkg-buildflags(1) — dpkg suite 💅

✨ NAME ✨

dpkg-buildflags — returns build flags to use during package build 🛠️

🦋 SYNOPSIS 🦋

dpkg-buildflags [option...] [command]

🌸 DESCRIPTION 🌸

Okay so bestie, dpkg-buildflags is literally the tool you use to retrieve compilation flags during a Debian package build. 💖

The default flags are defined by the vendor, but they can be extended/overridden in several ways:

system-wide with /etc/dpkg/buildflags.conf;
for the current user with $XDG_CONFIG_HOME/dpkg/buildflags.conf where $XDG_CONFIG_HOME defaults to $HOME/.config;
temporarily by the user with environment variables (see section "ENVIRONMENT");
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. Supported since dpkg 1.16.1.
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. Supported since dpkg 1.16.1.

The configuration files can contain comments on lines starting with a hash (#). Empty lines are also ignored.

This program was introduced in dpkg 1.15.7. 👑

💅 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 behavior 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.

Supported since dpkg 1.16.5. 🫶

--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. The flag values are quoted in shell syntax. Supported since dpkg 1.17.0.
- 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 behavior of the program: current vendor, relevant environment variables, feature areas, state of all feature flags, whether a feature is handled as a builtin default by the compiler, and the compiler flags with their origin.

For example:

 Vendor: Debian
 Environment:
  DEB_CFLAGS_SET=-O0 -Wall

 Area: qa
 Features:
  bug=no
  canary=no
 Builtins:

 Area: hardening
 Features:
  pie=no
 Builtins:
  pie=yes

 Area: reproducible
 Features:
  timeless=no
 Builtins:

 Flag: CFLAGS
 Value: -O0 -Wall
 Origin: env

 Flag: CPPFLAGS
 Value: -D_FORTIFY_SOURCE=2
 Origin: vendor

Support for Flag stanza since dpkg 1.19.0. Support for Builtins field in Area stanza since dpkg 1.21.14.

--query-features area — Print the features enabled for a given area. If the feature is handled (even if only on some architectures) as a builtin default by the compiler, then a Builtin field is printed. See the "FEATURE AREAS" section for more details about the currently recognized areas. Exits with 0 if the area is known otherwise exits with 1.

The output is in deb822(5) format, with one section per feature. For example:

 Feature: pie
 Enabled: yes
 Builtin: yes

 Feature: stackprotector
 Enabled: yes

Supported since dpkg 1.16.2. Support for Builtin field since dpkg 1.21.14.

--help — Show the usage message and exit.
--version — Show the version and exit.

🔥 SUPPORTED FLAGS 🔥

Here's the flag roster, bestie — names stay exactly as written, no renaming, periodt. 💅

ASFLAGS — Options for the host assembler. Default value: empty. Supported since dpkg 1.21.0.
CFLAGS — Options for the host 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 host C preprocessor. Default value: empty.
CXXFLAGS — Options for the host C++ compiler. Same as CFLAGS.
OBJCFLAGS — Options for the host Objective C compiler. Same as CFLAGS. Supported since dpkg 1.17.7.
OBJCXXFLAGS — Options for the host Objective C++ compiler. Same as CXXFLAGS. Supported since dpkg 1.17.7.
DFLAGS — Options for the host D compiler (ldc or gdc). Supported since dpkg 1.20.6.
FFLAGS — Options for the host Fortran 77 compiler. A subset of CFLAGS.
FCFLAGS — Options for the host Fortran 9x compiler. Same as FFLAGS. Supported since dpkg 1.17.7.
LDFLAGS — Options passed to the host compiler when linking executables or shared objects.

Note: It is not safe to pass this variable directly to ld(1), but if the variable needs to be passed anyway, then these options should be sanitized to allow only options known to work. In general -Wl, -l and -L options should be safe, with -Wl getting stripped and , in its arguments replaced with spaces. But whether any sanitized option is safe to be passed through, will depend on the intended semantics of the ld(1) invocation.

Default value: empty.

ASFLAGS_FOR_BUILD — Options for the build assembler. Default value: empty. Supported since dpkg 1.22.1.
CFLAGS_FOR_BUILD — Options for the build 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). Supported since dpkg 1.22.1.
CPPFLAGS_FOR_BUILD — Options for the build C preprocessor. Default value: empty. Supported since dpkg 1.22.1.
CXXFLAGS_FOR_BUILD — Options for the build C++ compiler. Same as CFLAGS_FOR_BUILD. Supported since dpkg 1.22.1.
OBJCFLAGS_FOR_BUILD — Options for the build Objective C compiler. Same as CFLAGS_FOR_BUILD. Supported since dpkg 1.22.1.
OBJCXXFLAGS_FOR_BUILD — Options for the build Objective C++ compiler. Same as CXXFLAGS_FOR_BUILD. Supported since dpkg 1.22.1.
DFLAGS_FOR_BUILD — Options for the build D compiler (ldc or gdc). Supported since dpkg 1.22.1.
FFLAGS_FOR_BUILD — Options for the build Fortran 77 compiler. A subset of CFLAGS_FOR_BUILD. Supported since dpkg 1.22.1.
FCFLAGS_FOR_BUILD — Options for the build Fortran 9x compiler. Same as FFLAGS_FOR_BUILD. Supported since dpkg 1.22.1.
LDFLAGS_FOR_BUILD — Options passed to the build compiler when linking executables or shared objects.

Default value: empty. Supported since dpkg 1.22.1.

New flags might be added in the future if the need arises (for example to support other languages).

🌈 FEATURE AREAS 🌈

Feature areas are currently vendor specific, and the ones described below are only recognized on Debian and derivatives.

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. Following the general syntax of these variables (described in dpkg-buildpackage(1)), multiple feature areas can be specified separated by spaces, where each get feature specifiers as mandatory parameters after an equal sign (=). The feature specifiers are comma-separated and parsed from left to right, where the settings within the same feature specifier override previous ones, even if the feature specifiers are split across multiple space-separated feature area settings for the same area.

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

okay so there's this one special feature called all — valid in any area — and ngl it's basically the "select all" button for build features. 💅 It lets you enable or disable every feature in an area in one go, no cap.

So say you want to nuke literally everything in the hardening area and then cherry-pick only format and fortify back in. It's giving:

export DEB_BUILD_MAINT_OPTIONS = hardening=-all,+format,+fortify

And you can set multiple feature areas at once, highkey iconic:

export DEB_BUILD_MAINT_OPTIONS = hardening=+pie abi=+lfs

The override behaviour applies as much to the all special feature as it does to specific features, which should allow for composition. 🧚 So if you want lfs on in the abi area, and only pie and fortify in the hardening area, but format only when CONDITION is defined, you'd do:

export DEB_BUILD_MAINT_OPTIONS = hardening=-all,+pie,+format abi=+lfs
…
DEB_BUILD_MAINT_OPTIONS += hardening=+fortify
ifdef CONDITION
DEB_BUILD_MAINT_OPTIONS += hardening=-format
endif

🌈 `abi` — the "we're touching the ABI, be normal about it" area

Several compile-time options (all detailed below, don't worry bestie) can be used to enable features that can change the ABI of a package. But they can't be enabled by default because, bestie, backwards compatibility — unless someone coordinates it or checks it individually. 🙈

🦋 `lfs`

This setting 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.

Note: the getconf(1) interface for querying LFS build flags, like LFS_CFLAGS or LFS_LDFLAGS, must not be used — that interface does not support cross-building. periodt. 💀

When this feature is enabled it will override the value from the same feature in the future feature area.

Disabled by default.

Supported since dpkg 1.22.0.

🦋 `time64`

This setting enables 64-bit time_t support on 32-bit architectures where their ABI does not include it by default, by adding -D_TIME_BITS=64 to CPPFLAGS. It also automatically enables the lfs feature from the abi feature area. cute little chain reaction ✨

If the setting is enabled explicitly then it gets enabled on all architectures including i386 but not hurd-i386 (where the kernel does not have time64 interfaces), ignoring the binary backwards compatibility default.

It is also enabled by default by gcc on the armel, armhf, hppa, m68k, mips, mipsel, powerpc and sh4 Debian architectures, where disabling the feature will add instead -U_LARGEFILE_SOURCE -U_FILE_OFFSET_BITS -U_TIME_BITS to CPPFLAGS.

Enabled by default except for i386 and hurd-i386 since dpkg 1.22.5.

Supported since dpkg 1.22.0.

🎀 `future` — stuff that should be default but can't be yet

Several compile-time options (detailed below, keep reading) can be used to enable features that should be enabled by default, but cannot due to backwards compatibility reasons. 😭

💜 `lfs`

This setting is now an alias for the lfs feature in the abi area — use that instead. The feature from the abi area overrides this setting.

Disabled by default.

Supported since dpkg 1.19.0.

🔥 `qa` — the vibe check for your source code

Several compile-time options (detailed below, obviously) can be used to help detect problems in the source code or build system. Think of it as your build snitching on you, but lovingly. 🫶

⭐ `bug-implicit-func`

This setting adds -Werror=implicit-function-declaration to CFLAGS.

Enabled by default since dpkg 1.22.6.

Supported since dpkg 1.22.3.

⭐ `bug`

This setting 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.

This feature handles -Werror=implicit-function-declaration via the bug-implicit-func feature, if that has not been specified.

Disabled by default.

Supported since dpkg 1.17.4.

⭐ `canary`

This setting 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. 🐤 (yes it's literally a canary in the coal mine, iykyk)

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.

Disabled by default.

Supported since dpkg 1.17.14.

⚡ `optimize` — make it go brrr (carefully)

Several compile-time options (detailed below, yes yes) can be used to help optimize a resulting binary.

Note: enabling all these options can result in unreproducible binary artifacts. 💀 not the reproducibility L, bestie.

Supported since dpkg 1.21.0.

🚀 `lto`

This setting enables Link Time Optimization by adding -flto=auto -ffat-lto-objects to CFLAGS, CXXFLAGS, OBJCFLAGS, OBJCXXFLAGS, FFLAGS, FCFLAGS and LDFLAGS.

Disabled by default.

Supported since dpkg 1.21.0.

🧪 `sanitize` — the "find the bugs at runtime" area

Several compile-time options (detailed below, promise) 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 — they can reduce reliability for conformant code, reduce security or even functionality. 🙈 like fr fr, these are for debugging, not for shipping.

🌸 `address`

This setting adds -fsanitize=address to LDFLAGS and -fsanitize=address -fno-omit-frame-pointer to CFLAGS and CXXFLAGS.

Disabled by default.

Supported since dpkg 1.18.0.

🌸 `thread`

This setting adds -fsanitize=thread to CFLAGS, CXXFLAGS and LDFLAGS.

Disabled by default.

Supported since dpkg 1.18.0.

🌸 `leak`

This setting adds -fsanitize=leak to LDFLAGS. It gets automatically disabled if either the address or the thread features are enabled, since they imply it. (the way that it just quietly steps aside 🫶)

Disabled by default.

Supported since dpkg 1.18.0.

🌸 `undefined`

This setting adds -fsanitize=undefined to CFLAGS, CXXFLAGS and LDFLAGS.

Disabled by default.

Supported since dpkg 1.18.0.

👑 `hardening` — bestie's armor

Several compile-time options (detailed below, we're almost there) 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 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’. 😭 ok that one's genuinely scary.

Enabled by default.

Supported since dpkg 1.16.1.

🎀 `fortify`

This setting 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.

Enabled by default.

Supported since dpkg 1.16.1.

🎀 `stackprotector`

This setting adds -fstack-protector --param=ssp-buffer-size=4 to CFLAGS, CXXFLAGS, OBJCFLAGS, OBJCXXFLAGS, 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). ✨ slay, honestly.

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.

Enabled by default if stackprotectorstrong is not in use.

Supported since dpkg 1.16.1.

🎀 `stackprotectorstrong`

This setting adds -fstack-protector-strong to CFLAGS, CXXFLAGS, OBJCFLAGS, OBJCXXFLAGS, FFLAGS and FCFLAGS. This is a stronger variant of stackprotector, but without significant performance penalties. 💅 ate and left no crumbs.

This feature has the same requirements as stackprotector, and in addition also requires gcc 4.9 and later.

Enabled by default. Disabling stackprotector will also disable this setting.

Supported since dpkg 1.17.11.

🎀 `stackclash`

This setting adds -fstack-clash-protection on amd64, arm64, armhf and armel to CFLAGS, CXXFLAGS, OBJCFLAGS, OBJCXXFLAGS, FFLAGS and FCFLAGS. This adds code to prevent stack clash style attacks.

Enabled by default.

Supported since dpkg 1.22.0.

🎀 `branch`

This setting adds -fcf-protection on amd64 and -mbranch-protection=standard on arm64 to CFLAGS, CXXFLAGS, OBJCFLAGS, OBJCXXFLAGS, FFLAGS and FCFLAGS. This adds branch protection to indirect calls, jumps and returns to check whether these are valid at run-time.

Enabled by default.

Supported since dpkg 1.22.0.

🎀 `relro`

This setting 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.

Enabled by default.

Supported since dpkg 1.16.1.

🎀 `bindnow`

This setting 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.

Disabled by default.

Supported since dpkg 1.16.1.

💅 `pie`

okay so this setting is the one that adds the required options to enable or disable PIE via gcc specs files — but only if needed, depending on whether gcc injects the flags on that architecture by itself or not. so it's very "i'll handle it, don't worry bestie" energy.

Let me break the four cases down because they're lowkey the whole point:

setting is enabled + gcc injects the flags → it adds nothing. zero. zilch. gcc already ate, no need to double up 💅
setting is enabled + gcc does not inject the flags → it adds -fPIE (via /usr/share/dpkg/pie-compiler.specs) to CFLAGS, CXXFLAGS, OBJCFLAGS, OBJCXXFLAGS, FFLAGS and FCFLAGS, and -fPIE -pie (via /usr/share/dpkg/pie-link.specs) to LDFLAGS
setting is disabled + gcc injects the flags → it adds -fno-PIE (via /usr/share/dpkg/no-pie-compile.specs) to CFLAGS, CXXFLAGS, OBJCFLAGS, OBJCXXFLAGS, FFLAGS and FCFLAGS, and -fno-PIE -no-pie (via /usr/share/dpkg/no-pie-link.specs) to LDFLAGS

Now, the lore: Position Independent Executable (PIE) is needed to take advantage of Address Space Layout Randomization (ASLR), which is supported by some kernel versions. So ASLR can already be enforced for data areas in the stack and heap (brk and mmap), but 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 built as PIE to gain ASLR. And when that happens, ROP (Return Oriented Programming) attacks are much harder, since there are no static locations to bounce off of during a memory corruption attack. it's giving security slay 🔥

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. so like, the specs machinery is carrying the team here 🫶

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. (sad. tragic. not recommended energy 🙈)
- -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's 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 — and this is the part that hurts 😭 — 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. good for them honestly 👑

No global default since dpkg 1.18.23, as it is enabled by default now by gcc on the amd64, arm64, armel, armhf, hurd-i386, i386, mips, mipsel, mips64el, powerpc, ppc64, ppc64el, riscv64, s390x, sparc and sparc64 Debian architectures.

Supported since dpkg 1.16.1.

🌸 `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. reproducible builds are literally the moment, we stan 🌈

⏰ `timeless`

This setting adds -Wdate-time to CPPFLAGS. This will cause warnings when the __TIME__, __DATE__ and __TIMESTAMP__ macros are used. (yes bestie, we will find out if you baked a timestamp into the binary 💀)

Enabled by default.

Supported since dpkg 1.17.14.

🗺️ `fixfilepath`

This setting adds -ffile-prefix-map=BUILDPATH=. to CFLAGS, CXXFLAGS, OBJCFLAGS, OBJCXXFLAGS, 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 file. bye bye /home/yourname/whatever leaking into everything 🦋

If both fixdebugpath and fixfilepath are set, this option takes precedence, because it is a superset of the former.

Note: If the build process captures the build flags into the resulting built objects, that will make the package unreproducible. And while disabling this option might make some of the objects reproducible again, this would also require disabling fixdebugpath, which might make any generated debug symbols objects unreproducible. The ideal fix is to stop capturing build flags. like... just don't do it 😭

Enabled by default.

Supported since dpkg 1.19.1.

🐛 `fixdebugpath`

This setting adds -fdebug-prefix-map=BUILDPATH=. to CFLAGS, CXXFLAGS, OBJCFLAGS, OBJCXXFLAGS, 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. same vibe, debug edition 💜

Note: This feature has similar reproducible properties as fixfilepath.

Enabled by default.

Supported since dpkg 1.18.5.

🌿 ENVIRONMENT

okay so there are 2 sets of environment variables doing the same operations, and the distinction matters, bestie, so pay attention:

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. like, that's the whole boundary, please respect it 🫶

DEB_flag_SET, DEB_flag_MAINT_SET — This variable can be used to force the value returned for the given flag. (Support for DEB_flag_MAINT_SET since dpkg 1.16.1.)
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. (Supported since dpkg 1.16.1.)
DEB_flag_APPEND, DEB_flag_MAINT_APPEND — This variable can be used to append supplementary options to the value returned for the given flag. (Support for DEB_flag_MAINT_APPEND since dpkg 1.16.1.)
DEB_flag_PREPEND, DEB_flag_MAINT_PREPEND — This variable can be used to prepend supplementary options to the value returned for the given flag. (Supported since dpkg 1.16.1.)
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. Some build profiles might currently require their counterpart to also be included in the build options; the list of such build profiles is vendor specific. For more information about build profiles, see dpkg-buildpackage(1). (Support for DEB_BUILD_MAINT_OPTIONS since dpkg 1.16.1.)
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 to use in features such as fixdebugpath so that they can be controlled by the caller. This variable is currently Debian and derivatives-specific. (Supported since dpkg 1.18.8.)
DEB_HOST_ARCH — Sets the host architecture. This affects the build flags that are emitted, which is typically relevant when cross-compiling, where DEB_HOST_ARCH is different to DEB_BUILD_ARCH.
DPKG_COLORS — Sets the color mode. The currently accepted values are: auto (default), always and never. (Supported since dpkg 1.18.5.) 🎀
DPKG_NLS — If set, it will be used to decide whether to activate Native Language Support, also known as internationalization (or i18n) support. The accepted values are: 0 and 1 (default). (Supported since dpkg 1.19.0.)

📁 FILES

🛠️ Configuration files

/etc/dpkg/buildflags.conf — System wide configuration file. the big one 👑
$XDG_CONFIG_HOME/dpkg/buildflags.conf
$HOME/.config/dpkg/buildflags.conf — User configuration file. your own personal little corner 💖

📦 Packaging support

/usr/share/dpkg/buildflags.mk — Makefile snippet that loads (and optionally exports) all flags supported by dpkg-buildflags into variables. (Supported since dpkg 1.16.1.)
/usr/share/dpkg/buildtools.mk — Makefile snippet that sets suitable host and build tools (and optionally exports them) into variables. (Supported since dpkg 1.19.0.)

✨ EXAMPLES ✨

Okay bestie, here's the part where we actually do the thing 💅

🎀 Usage in debian/rules 🎀

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

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. 😭 so like… please don't.

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. iconic behaviour, honestly ✨

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 pass the flags to commands manually:

include /usr/share/dpkg/buildflags.mk
build-arch:
       $(CC) -o hello hello.c $(CPPFLAGS) $(CFLAGS) $(LDFLAGS)

and that's the whole page, bestie!! 🦋 go forth and build 💜

This was dpkg-buildflags(1) — version 1.23.11-dirty, dated 2026-09-09. mwah 💋 slay, and remember: no cap, just flags. 🎀

📦 where this page comes from

arch rolling: dpkg 1.23.11-1 · GPL-2.0-or-later
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash-1017 on 2026-11-04: a language model's rewrite of the original, under its terms

dpkg-buildflags(1)