xref: /rk3399_ARM-atf/docs/getting_started/build-options.rst (revision 2f5fd8267a2159338924d6fcaa0b30de98b1aa0c)

Build Options
=============

The TF-A build system supports the following build options. Unless mentioned
otherwise, these options are expected to be specified at the build command
line and are not to be modified in any component makefiles. Note that the
build system doesn't track dependency for build options. Therefore, if any of
the build options are changed from a previous build, a clean build must be
performed.

.. _build_options_common:

Common build options
--------------------

-  ``AARCH32_INSTRUCTION_SET``: Choose the AArch32 instruction set that the
   compiler should use. Valid values are T32 and A32. It defaults to T32 due to
   code having a smaller resulting size.

-  ``AARCH32_SP`` : Choose the AArch32 Secure Payload component to be built as
   as the BL32 image when ``ARCH=aarch32``. The value should be the path to the
   directory containing the SP source, relative to the ``bl32/``; the directory
   is expected to contain a makefile called ``<aarch32_sp-value>.mk``.

-  ``AMU_RESTRICT_COUNTERS``: Register reads to the group 1 counters will return
   zero at all but the highest implemented exception level. External
   memory-mapped debug accesses are unaffected by this control.
   The default value is 1 for all platforms.

-  ``ARCH`` : Choose the target build architecture for TF-A. It can take either
   ``aarch64`` or ``aarch32`` as values. By default, it is defined to
   ``aarch64``.

-  ``ARM_ARCH_FEATURE``: Optional Arm Architecture build option which specifies
   one or more feature modifiers. This option has the form ``[no]feature+...``
   and defaults to ``none``. It translates into compiler option
   ``-march=armvX[.Y]-a+[no]feature+...``. See compiler's documentation for the
   list of supported feature modifiers.

-  ``ARM_ARCH_MAJOR``: The major version of Arm Architecture to target when
   compiling TF-A. Its value must be numeric, and defaults to 8 . See also,
   *Armv8 Architecture Extensions* and *Armv7 Architecture Extensions* in
   :ref:`Firmware Design`.

-  ``ARM_ARCH_MINOR``: The minor version of Arm Architecture to target when
   compiling TF-A. Its value must be a numeric, and defaults to 0. See also,
   *Armv8 Architecture Extensions* in :ref:`Firmware Design`.

-  ``ARM_BL2_SP_LIST_DTS``: Path to DTS file snippet to override the hardcoded
   SP nodes in tb_fw_config.

-  ``ARM_SPMC_MANIFEST_DTS`` : path to an alternate manifest file used as the
   SPMC Core manifest. Valid when ``SPD=spmd`` is selected.

-  ``BL2``: This is an optional build option which specifies the path to BL2
   image for the ``fip`` target. In this case, the BL2 in the TF-A will not be
   built.

-  ``BL2U``: This is an optional build option which specifies the path to
   BL2U image. In this case, the BL2U in TF-A will not be built.

-  ``RESET_TO_BL2``: Boolean option to enable BL2 entrypoint as the CPU reset
   vector instead of the BL1 entrypoint. It can take the value 0 (CPU reset to BL1
   entrypoint) or 1 (CPU reset to BL2 entrypoint).
   The default value is 0.

-  ``BL2_RUNS_AT_EL3``: This is an implicit flag to denote that BL2 runs at EL3.
   While it is explicitly set to 1 when RESET_TO_BL2 is set to 1 it can also be
   true in a 4-world system where RESET_TO_BL2 is 0.

-  ``BL2_ENABLE_SP_LOAD``: Boolean option to enable loading SP packages from the
   FIP. Automatically enabled if ``SP_LAYOUT_FILE`` is provided.

-  ``BL2_IN_XIP_MEM``: In some use-cases BL2 will be stored in eXecute In Place
   (XIP) memory, like BL1. In these use-cases, it is necessary to initialize
   the RW sections in RAM, while leaving the RO sections in place. This option
   enable this use-case. For now, this option is only supported
   when RESET_TO_BL2 is set to '1'.

-  ``BL31``: This is an optional build option which specifies the path to
   BL31 image for the ``fip`` target. In this case, the BL31 in TF-A will not
   be built.

-  ``BL31_KEY``: This option is used when ``GENERATE_COT=1``. It specifies a
   file that contains the BL31 private key in PEM format or a PKCS11 URI. If
   ``SAVE_KEYS=1``, only a file is accepted and it will be used to save the key.

-  ``BL32``: This is an optional build option which specifies the path to
   BL32 image for the ``fip`` target. In this case, the BL32 in TF-A will not
   be built.

-  ``BL32_EXTRA1``: This is an optional build option which specifies the path to
   Trusted OS Extra1 image for the  ``fip`` target.

-  ``BL32_EXTRA2``: This is an optional build option which specifies the path to
   Trusted OS Extra2 image for the ``fip`` target.

-  ``BL32_KEY``: This option is used when ``GENERATE_COT=1``. It specifies a
   file that contains the BL32 private key in PEM format or a PKCS11 URI. If
   ``SAVE_KEYS=1``, only a file is accepted and it will be used to save the key.

-  ``RMM``: This is an optional build option used when ``ENABLE_RME`` is set.
   It specifies the path to RMM binary for the ``fip`` target. If the RMM option
   is not specified, TF-A builds the TRP to load and run at R-EL2.

-  ``BL33``: Path to BL33 image in the host file system. This is mandatory for
   ``fip`` target in case TF-A BL2 is used.

-  ``BL33_KEY``: This option is used when ``GENERATE_COT=1``. It specifies a
   file that contains the BL33 private key in PEM format or a PKCS11 URI. If
   ``SAVE_KEYS=1``, only a file is accepted and it will be used to save the key.

-  ``BRANCH_PROTECTION``: Numeric value to enable ARMv8.3 Pointer Authentication
   and ARMv8.5 Branch Target Identification support for TF-A BL images themselves.
   If enabled, it is needed to use a compiler that supports the option
   ``-mbranch-protection``. The value of the ``-march`` (via ``ARM_ARCH_MINOR``
   and ``ARM_ARCH_MAJOR``) option will control which instructions will be
   emitted (HINT space or not). Selects the branch protection features to use:
-  0: Default value turns off all types of branch protection (FEAT_STATE_DISABLED)
-  1: Enables all types of branch protection features
-  2: Return address signing to its standard level
-  3: Extend the signing to include leaf functions
-  4: Turn on branch target identification mechanism
-  5: Enables all types of branch protection features, only if present in
   hardware (FEAT_STATE_CHECK).

   The table below summarizes ``BRANCH_PROTECTION`` values, GCC compilation options
   and resulting PAuth/BTI features.

   +-------+--------------+-------+-----+
   | Value |  GCC option  | PAuth | BTI |
   +=======+==============+=======+=====+
   |   0   |     none     |   N   |  N  |
   +-------+--------------+-------+-----+
   |   1   |   standard   |   Y   |  Y  |
   +-------+--------------+-------+-----+
   |   2   |   pac-ret    |   Y   |  N  |
   +-------+--------------+-------+-----+
   |   3   | pac-ret+leaf |   Y   |  N  |
   +-------+--------------+-------+-----+
   |   4   |     bti      |   N   |  Y  |
   +-------+--------------+-------+-----+
   |   5   |   dynamic    |   Y   |  Y  |
   +-------+--------------+-------+-----+

   This option defaults to 0.
   Note that Pointer Authentication is enabled for Non-secure world
   irrespective of the value of this option if the CPU supports it.

-  ``BUILD_MESSAGE_TIMESTAMP``: String used to identify the time and date of the
   compilation of each build. It must be set to a C string (including quotes
   where applicable). Defaults to a string that contains the time and date of
   the compilation.

-  ``BUILD_STRING``: Input string for VERSION_STRING, which allows the TF-A
   build to be uniquely identified. Defaults to the current git commit id.

-  ``BUILD_BASE``: Output directory for the build. Defaults to ``./build``

-  ``CFLAGS``: Extra user options appended on the compiler's command line in
   addition to the options set by the build system.

-  ``COLD_BOOT_SINGLE_CPU``: This option indicates whether the platform may
   release several CPUs out of reset. It can take either 0 (several CPUs may be
   brought up) or 1 (only one CPU will ever be brought up during cold reset).
   Default is 0. If the platform always brings up a single CPU, there is no
   need to distinguish between primary and secondary CPUs and the boot path can
   be optimised. The ``plat_is_my_cpu_primary()`` and
   ``plat_secondary_cold_boot_setup()`` platform porting interfaces do not need
   to be implemented in this case.

-  ``COT``: When Trusted Boot is enabled, selects the desired chain of trust.
   Defaults to ``tbbr``.

-  ``CRASH_REPORTING``: A non-zero value enables a console dump of processor
   register state when an unexpected exception occurs during execution of
   BL31. This option defaults to the value of ``DEBUG`` - i.e. by default
   this is only enabled for a debug build of the firmware.

-  ``CREATE_KEYS``: This option is used when ``GENERATE_COT=1``. It tells the
   certificate generation tool to create new keys in case no valid keys are
   present or specified. Allowed options are '0' or '1'. Default is '1'.

-  ``CTX_INCLUDE_AARCH32_REGS`` : Boolean option that, when set to 1, will cause
   the AArch32 system registers to be included when saving and restoring the
   CPU context. The option must be set to 0 for AArch64-only platforms (that
   is on hardware that does not implement AArch32, or at least not at EL1 and
   higher ELs). Default value is 1.

-  ``CTX_INCLUDE_FPREGS``: Boolean option that, when set to 1, will cause the FP
   registers to be included when saving and restoring the CPU context. Default
   is 0.

-  ``CTX_INCLUDE_MPAM_REGS``: Boolean option that, when set to 1, will cause the
   Memory System Resource Partitioning and Monitoring (MPAM)
   registers to be included when saving and restoring the CPU context.
   Default is '0'.

-  ``CTX_INCLUDE_NEVE_REGS``: Numeric value, when set will cause the Armv8.4-NV
   registers to be saved/restored when entering/exiting an EL2 execution
   context. This flag can take values 0 to 2, to align with the
   ``ENABLE_FEAT`` mechanism. Default value is 0.

-  ``CTX_INCLUDE_PAUTH_REGS``: Numeric value to enable the Pointer
   Authentication for Secure world. This will cause the ARMv8.3-PAuth registers
   to be included when saving and restoring the CPU context as part of world
   switch. Automatically enabled when ``BRANCH_PROTECTION`` is enabled. This flag
   can take values 0 to 2, to align with ``ENABLE_FEAT`` mechanism. Default value
   is 0.

   Note that Pointer Authentication is enabled for Non-secure world irrespective
   of the value of this flag if the CPU supports it. Alternatively, when
   ``BRANCH_PROTECTION`` is enabled, this flag is superseded.

-  ``CTX_INCLUDE_SVE_REGS``: Boolean option that, when set to 1, will cause the
   SVE registers to be included when saving and restoring the CPU context. Note
   that this build option requires ``ENABLE_SVE_FOR_SWD`` to be enabled. In
   general, it is recommended to perform SVE context management in lower ELs
   and skip in EL3 due to the additional cost of maintaining large data
   structures to track the SVE state. Hence, the default value is 0.

-  ``DEBUG``: Chooses between a debug and release build. It can take either 0
   (release) or 1 (debug) as values. 0 is the default.

-  ``DECRYPTION_SUPPORT``: This build flag enables the user to select the
   authenticated decryption algorithm to be used to decrypt firmware/s during
   boot. It accepts 2 values: ``aes_gcm`` and ``none``. The default value of
   this flag is ``none`` to disable firmware decryption which is an optional
   feature as per TBBR.

-  ``DISABLE_BIN_GENERATION``: Boolean option to disable the generation
   of the binary image. If set to 1, then only the ELF image is built.
   0 is the default.

-  ``DISABLE_MTPMU``: Numeric option to disable ``FEAT_MTPMU`` (Multi Threaded
   PMU). ``FEAT_MTPMU`` is an optional feature available on Armv8.6 onwards.
   This flag can take values 0 to 2, to align with the ``ENABLE_FEAT``
   mechanism. Default is ``0``.

-  ``DYN_DISABLE_AUTH``: Provides the capability to dynamically disable Trusted
   Board Boot authentication at runtime. This option is meant to be enabled only
   for development platforms. ``TRUSTED_BOARD_BOOT`` flag must be set if this
   flag has to be enabled. 0 is the default.

-  ``E``: Boolean option to make warnings into errors. Default is 1.

   When specifying higher warnings levels (``W=1`` and higher), this option
   defaults to 0. This is done to encourage contributors to use them, as they
   are expected to produce warnings that would otherwise fail the build. New
   contributions are still expected to build with ``W=0`` and ``E=1`` (the
   default).

-  ``EARLY_CONSOLE``: This option is used to enable early traces before default
   console is properly setup. It introduces EARLY_* traces macros, that will
   use the non-EARLY traces macros if the flag is enabled, or do nothing
   otherwise. To use this feature, platforms will have to create the function
   plat_setup_early_console().
   Default is 0 (disabled)

-  ``EL3_PAYLOAD_BASE``: This option enables booting an EL3 payload instead of
   the normal boot flow. It must specify the entry point address of the EL3
   payload. Please refer to the "Booting an EL3 payload" section for more
   details.

-  ``ENABLE_AMU_AUXILIARY_COUNTERS``: Enables support for AMU auxiliary counters
   (also known as group 1 counters). These are implementation-defined counters,
   and as such require additional platform configuration. Default is 0.

-  ``ENABLE_ASSERTIONS``: This option controls whether or not calls to ``assert()``
   are compiled out. For debug builds, this option defaults to 1, and calls to
   ``assert()`` are left in place. For release builds, this option defaults to 0
   and calls to ``assert()`` function are compiled out. This option can be set
   independently of ``DEBUG``. It can also be used to hide any auxiliary code
   that is only required for the assertion and does not fit in the assertion
   itself.

-  ``ENABLE_BACKTRACE``: This option controls whether to enable backtrace
   dumps or not. It is supported in both AArch64 and AArch32. However, in
   AArch32 the format of the frame records are not defined in the AAPCS and they
   are defined by the implementation. This implementation of backtrace only
   supports the format used by GCC when T32 interworking is disabled. For this
   reason enabling this option in AArch32 will force the compiler to only
   generate A32 code. This option is enabled by default only in AArch64 debug
   builds, but this behaviour can be overridden in each platform's Makefile or
   in the build command line.

-  ``ENABLE_FEAT``
   The Arm architecture defines several architecture extension features,
   named FEAT_xxx in the architecure manual. Some of those features require
   setup code in higher exception levels, other features might be used by TF-A
   code itself.
   Most of the feature flags defined in the TF-A build system permit to take
   the values 0, 1 or 2, with the following meaning:

   ::

     ENABLE_FEAT_* = 0: Feature is disabled statically at compile time.
     ENABLE_FEAT_* = 1: Feature is enabled unconditionally at compile time.
     ENABLE_FEAT_* = 2: Feature is enabled, but checked at runtime.

   When setting the flag to 0, the feature is disabled during compilation,
   and the compiler's optimisation stage and the linker will try to remove
   as much of this code as possible.
   If it is defined to 1, the code will use the feature unconditionally, so the
   CPU is expected to support that feature. The FEATURE_DETECTION debug
   feature, if enabled, will verify this.
   If the feature flag is set to 2, support for the feature will be compiled
   in, but its existence will be checked at runtime, so it works on CPUs with
   or without the feature. This is mostly useful for platforms which either
   support multiple different CPUs, or where the CPU is configured at runtime,
   like in emulators.

-  ``ENABLE_FEAT_AMU``: Numeric value to enable Activity Monitor Unit
   extensions. This flag can take the values 0 to 2, to align with the
   ``ENABLE_FEAT`` mechanism. This is an optional architectural feature
   available on v8.4 onwards. Some v8.2 implementations also implement an AMU
   and this option can be used to enable this feature on those systems as well.
   This flag can take the values 0 to 2, the default is 0.

-  ``ENABLE_FEAT_AMUv1p1``: Numeric value to enable the ``FEAT_AMUv1p1``
   extension. ``FEAT_AMUv1p1`` is an optional feature available on Arm v8.6
   onwards. This flag can take the values 0 to 2, to align with the
   ``ENABLE_FEAT`` mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_CSV2_2``: Numeric value to enable the ``FEAT_CSV2_2``
   extension. It allows access to the SCXTNUM_EL2 (Software Context Number)
   register during EL2 context save/restore operations. ``FEAT_CSV2_2`` is an
   optional feature available on Arm v8.0 onwards. This flag can take values
   0 to 2, to align with the ``ENABLE_FEAT`` mechanism.
   Default value is ``0``.

-  ``ENABLE_FEAT_CSV2_3``: Numeric value to enable support for ``FEAT_CSV2_3``
   extension. This feature is supported in AArch64 state only and is an optional
   feature available in Arm v8.0 implementations.
   ``FEAT_CSV2_3`` implies the implementation of ``FEAT_CSV2_2``.
   The flag can take values 0 to 2, to align with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

- ``ENABLE_FEAT_DEBUGV8P9``: Numeric value to enable ``FEAT_DEBUGV8P9``
   extension which allows the ability to implement more than 16 breakpoints
   and/or watchpoints. This feature is mandatory from v8.9 and is optional
   from v8.8. This flag can take the values of 0 to 2, to align with the
   ``ENABLE_FEAT`` mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_DIT``: Numeric value to enable ``FEAT_DIT`` (Data Independent
   Timing) extension. It allows setting the ``DIT`` bit of PSTATE in EL3.
   ``FEAT_DIT`` is a mandatory  architectural feature and is enabled from v8.4
   and upwards. This flag can take the values 0 to 2, to align  with the
   ``ENABLE_FEAT`` mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_ECV``: Numeric value to enable support for the Enhanced Counter
   Virtualization feature, allowing for access to the CNTPOFF_EL2 (Counter-timer
   Physical Offset register) during EL2 to EL3 context save/restore operations.
   Its a mandatory architectural feature and is enabled from v8.6 and upwards.
   This flag can take the values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_FPMR``: Numerical value to enable support for Floating Point
   Mode Register feature, allowing access to the FPMR register. FPMR register
   controls the behaviors of FP8 instructions. It is an optional architectural
   feature from v9.2 and upwards. This flag can take value of 0 to 2, to align
   with the ``FEATURE_DETECTION`` mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_FGT``: Numeric value to enable support for FGT (Fine Grain Traps)
   feature allowing for access to the HDFGRTR_EL2 (Hypervisor Debug Fine-Grained
   Read Trap Register) during EL2 to EL3 context save/restore operations.
   Its a mandatory architectural feature and is enabled from v8.6 and upwards.
   This flag can take the values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_FGT2``: Numeric value to enable support for FGT2
   (Fine Grain Traps 2) feature allowing for access to Fine-grained trap 2 registers
   during  EL2 to EL3 context save/restore operations.
   Its an optional architectural feature and is available from v8.8 and upwards.
   This flag can take the values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_FGWTE3``: Numeric value to enable support for
   Fine Grained Write Trap EL3 (FEAT_FGWTE3), a feature that allows EL3 to
   restrict overwriting certain EL3 registers after boot.
   This lockdown is established by setting individual trap bits for
   system registers that are not expected to be overwritten after boot.
   This feature is an optional architectural feature and is available from
   Armv9.4 onwards. This flag can take values from 0 to 2, aligning with
   the ``ENABLE_FEAT`` mechanism. The default value is 0.

   .. note::
      This feature currently traps access to all EL3 registers in
      ``FGWTE3_EL3``, except for ``MDCR_EL3``, ``MPAM3_EL3``,
      ``TPIDR_EL3``(when ``CRASH_REPORTING=1``), and
      ``SCTLR_EL3``(when ``HW_ASSISTED_COHERENCY=0``).
      If additional traps need to be disabled for specific platforms,
      please contact the Arm team on `TF-A public mailing list`_.

-  ``ENABLE_FEAT_HCX``: Numeric value to set the bit SCR_EL3.HXEn in EL3 to
   allow access to HCRX_EL2 (extended hypervisor control register) from EL2 as
   well as adding HCRX_EL2 to the EL2 context save/restore operations. Its a
   mandatory architectural feature and is enabled from v8.7 and upwards. This
   flag can take the values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

- ``ENABLE_FEAT_MOPS``: Numeric value to enable FEAT_MOPS (Standardization
   of memory operations) when INIT_UNUSED_NS_EL2=1.
   This feature is mandatory from v8.8 and enabling of FEAT_MOPS does not
   require any settings from EL3 as the controls are present in EL2 registers
   (HCRX_EL2.{MSCEn,MCE2} and SCTLR_EL2.MSCEn) and in most configurations
   we expect EL2 to be present. But in case of INIT_UNUSED_NS_EL2=1 ,
   EL3 should configure the EL2 registers. This flag
   can take values 0 to 2, to align with the ``ENABLE_FEAT`` mechanism.
   Default value is ``0``.

-  ``ENABLE_FEAT_MTE2``: Numeric value to enable Memory Tagging Extension2
   if the platform wants to use this feature and MTE2 is enabled at ELX.
   This flag can take values 0 to 2, to align with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_PAN``: Numeric value to enable the ``FEAT_PAN`` (Privileged
   Access Never) extension. ``FEAT_PAN`` adds a bit to PSTATE, generating a
   permission fault for any privileged data access from EL1/EL2 to virtual
   memory address, accessible at EL0, provided (HCR_EL2.E2H=1). It is a
   mandatory architectural feature and is enabled from v8.1 and upwards. This
   flag can take values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_PAUTH_LR``: Numeric value to enable the ``FEAT_PAUTH_LR``
   extension. ``FEAT_PAUTH_LR`` is an optional feature available from Arm v9.4
   onwards. This feature requires PAUTH to be enabled via the
   ``BRANCH_PROTECTION`` flag. This flag can take the values 0 to 2, to align
   with the ``ENABLE_FEAT`` mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_RNG``: Numeric value to enable the ``FEAT_RNG`` extension.
   ``FEAT_RNG`` is an optional feature available on Arm v8.5 onwards. This
   flag can take the values 0 to 2, to align with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_RNG_TRAP``: Numeric value to enable the ``FEAT_RNG_TRAP``
   extension. This feature is only supported in AArch64 state. This flag can
   take values 0 to 2, to align with the ``ENABLE_FEAT`` mechanism.
   Default value is ``0``. ``FEAT_RNG_TRAP`` is an optional feature from
   Armv8.5 onwards.

-  ``ENABLE_FEAT_SB``: Boolean option to let the TF-A code use the ``FEAT_SB``
   (Speculation Barrier) instruction ``FEAT_SB`` is an optional feature and
   defaults to ``0`` for pre-Armv8.5 CPUs, but is mandatory for Armv8.5 or
   later CPUs. It is enabled from v8.5 and upwards and if needed can be
   overidden from platforms explicitly.

-  ``ENABLE_FEAT_SEL2``: Numeric value to enable the ``FEAT_SEL2`` (Secure EL2)
   extension. ``FEAT_SEL2`` is a mandatory feature available on Arm v8.4.
   This flag can take values 0 to 2, to align with the ``ENABLE_FEAT``
   mechanism. Default is ``0``.

-  ``ENABLE_FEAT_TWED``: Numeric value to enable the ``FEAT_TWED`` (Delayed
   trapping of WFE Instruction) extension. ``FEAT_TWED`` is a optional feature
   available on Arm v8.6. This flag can take values 0 to 2, to align with the
   ``ENABLE_FEAT`` mechanism. Default is ``0``.

    When ``ENABLE_FEAT_TWED`` is set to ``1``, WFE instruction trapping gets
    delayed by the amount of value in ``TWED_DELAY``.

-  ``ENABLE_FEAT_VHE``: Numeric value to enable the ``FEAT_VHE`` (Virtualization
   Host Extensions) extension. It allows access to CONTEXTIDR_EL2 register
   during EL2 context save/restore operations.``FEAT_VHE`` is a mandatory
   architectural feature and is enabled from v8.1 and upwards. It can take
   values 0 to 2, to align  with the ``ENABLE_FEAT`` mechanism.
   Default value is ``0``.

-  ``ENABLE_FEAT_TCR2``: Numeric value to set the bit SCR_EL3.ENTCR2 in EL3 to
   allow access to TCR2_EL2 (extended translation control) from EL2 as
   well as adding TCR2_EL2 to the EL2 context save/restore operations. Its a
   mandatory architectural feature and is enabled from v8.9 and upwards. This
   flag can take the values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_S2PIE``: Numeric value to enable support for FEAT_S2PIE
   at EL2 and below, and context switch relevant registers.  This flag
   can take the values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_S1PIE``: Numeric value to enable support for FEAT_S1PIE
   at EL2 and below, and context switch relevant registers.  This flag
   can take the values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_S2POE``: Numeric value to enable support for FEAT_S2POE
   at EL2 and below, and context switch relevant registers.  This flag
   can take the values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_S1POE``: Numeric value to enable support for FEAT_S1POE
   at EL2 and below, and context switch relevant registers.  This flag
   can take the values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_GCS``: Numeric value to set the bit SCR_EL3.GCSEn in EL3 to
   allow use of Guarded Control Stack from EL2 as well as adding the GCS
   registers to the EL2 context save/restore operations. This flag can take
   the values 0 to 2, to align  with the ``ENABLE_FEAT`` mechanism.
   Default value is ``0``.

 - ``ENABLE_FEAT_GCIE``: Boolean value to enable support for the GICv5 CPU
   interface (see ``USE_GIC_DRIVER`` for the IRI). GICv5 and GICv3 are mutually
   exclusive, so the ``ENABLE_FEAT`` mechanism is currently not supported.
   Default value is ``0``.

-  ``ENABLE_FEAT_THE``: Numeric value to enable support for FEAT_THE
   (Translation Hardening Extension) at EL2 and below, setting the bit
   SCR_EL3.RCWMASKEn in EL3 to allow access to RCWMASK_EL1 and RCWSMASK_EL1
   registers and context switch them.
   Its an optional architectural feature and is available from v8.8 and upwards.
   This flag can take the values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_SCTLR2``: Numeric value to enable support for FEAT_SCTLR2
   (Extension to SCTLR_ELx) at EL2 and below, setting the bit
   SCR_EL3.SCTLR2En in EL3 to allow access to SCTLR2_ELx registers and
   context switch them. This feature is OPTIONAL from Armv8.0 implementations
   and mandatory in Armv8.9 implementations.
   This flag can take the values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_FEAT_D128``: Numeric value to enable support for FEAT_D128
   at EL2 and below, setting the bit SCT_EL3.D128En in EL3 to allow access to
   128 bit version of system registers like PAR_EL1, TTBR0_EL1, TTBR1_EL1,
   TTBR0_EL2, TTBR1_EL2, TTBR0_EL12, TTBR1_EL12 , VTTBR_EL2, RCWMASK_EL1, and
   RCWSMASK_EL1. Its an optional architectural feature and is available from
   9.3 and upwards.
   This flag can take the values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. Default value is ``0``.

-  ``ENABLE_LTO``: Boolean option to enable Link Time Optimization (LTO)
   support in GCC for TF-A. This option is currently only supported for
   AArch64. Default is 0.

-  ``ENABLE_FEAT_MPAM``: Numeric value to enable lower ELs to use MPAM
   feature. MPAM is an optional Armv8.4 extension that enables various memory
   system components and resources to define partitions; software running at
   various ELs can assign themselves to desired partition to control their
   performance aspects.

   This flag can take values 0 to 2, to align  with the ``ENABLE_FEAT``
   mechanism. When this option is set to ``1`` or ``2``, EL3 allows lower ELs to
   access their own MPAM registers without trapping into EL3. This option
   doesn't make use of partitioning in EL3, however. Platform initialisation
   code should configure and use partitions in EL3 as required. This option
   defaults to ``2`` since MPAM is enabled by default for NS world only.
   The flag is automatically disabled when the target
   architecture is AArch32.

-  ``ENABLE_FEAT_MPAM_PE_BW_CTRL``: This option enables Armv9.3 MPAM
   PE-side bandwidth controls and disables traps to EL3/EL2 (when
   ``INIT_UNUSED_NS_EL2`` = 1). The flag accepts values from 0 to 2, in
   line with the ``ENABLE_FEAT`` mechanism, and defaults to ``0``.

-  ``ENABLE_FEAT_LS64_ACCDATA``: Numeric value to enable access and save and
   restore the ACCDATA_EL1 system register, at EL2 and below. This flag can
   take the values 0 to 2, to align  with the ``ENABLE_FEAT`` mechanism.
   Default value is ``0``.

-  ``ENABLE_MPMM``: Boolean option to enable support for the Maximum Power
   Mitigation Mechanism supported by certain Arm cores, which allows the SoC
   firmware to detect and limit high activity events to assist in SoC processor
   power domain dynamic power budgeting and limit the triggering of whole-rail
   (i.e. clock chopping) responses to overcurrent conditions. Defaults to ``0``.

-  ``ENABLE_PIE``: Boolean option to enable Position Independent Executable(PIE)
   support within generic code in TF-A. This option is currently only supported
   in BL2, BL31, and BL32 (TSP) for AARCH64 binaries, and
   in BL32 (SP_min) for AARCH32. Default is 0.

-  ``ENABLE_PMF``: Boolean option to enable support for optional Performance
   Measurement Framework(PMF). Default is 0.

-  ``ENABLE_PSCI_STAT``: Boolean option to enable support for optional PSCI
   functions ``PSCI_STAT_RESIDENCY`` and ``PSCI_STAT_COUNT``. Default is 0.
   In the absence of an alternate stat collection backend, ``ENABLE_PMF`` must
   be enabled. If ``ENABLE_PMF`` is set, the residency statistics are tracked in
   software.

-  ``ENABLE_RUNTIME_INSTRUMENTATION``: Boolean option to enable runtime
   instrumentation which injects timestamp collection points into TF-A to
   allow runtime performance to be measured. Currently, only PSCI is
   instrumented. Enabling this option enables the ``ENABLE_PMF`` build option
   as well. Default is 0.

-  ``ENABLE_SPE_FOR_NS`` : Numeric value to enable Statistical Profiling
   extensions. This is an optional architectural feature for AArch64.
   This flag can take the values 0 to 2, to align with the ``ENABLE_FEAT``
   mechanism. The default is 2 but is automatically disabled when the target
   architecture is AArch32.

-  ``ENABLE_SVE_FOR_NS``: Numeric value to enable Scalable Vector Extension
   (SVE) for the Non-secure world only. SVE is an optional architectural feature
   for AArch64. This flag can take the values 0 to 2, to align with the
   ``ENABLE_FEAT`` mechanism. At this time, this build option cannot be used on
   systems that have SPM_MM enabled. The default value is 2.

   Note that when SVE is enabled for the Non-secure world, access
   to SVE, SIMD and floating-point functionality from the Secure world is
   independently controlled by build option ``ENABLE_SVE_FOR_SWD``. When enabling
   ``CTX_INCLUDE_FPREGS`` and ``ENABLE_SVE_FOR_NS`` together, it is mandatory to
   enable ``CTX_INCLUDE_SVE_REGS``. This is to avoid corruption of the Non-secure
   world data in the Z-registers which are aliased by the SIMD and FP registers.

-  ``ENABLE_SVE_FOR_SWD``: Boolean option to enable SVE and FPU/SIMD functionality
   for the Secure world. SVE is an optional architectural feature for AArch64.
   The default is 0 and it is automatically disabled when the target architecture
   is AArch32.

   .. note::
      This build flag requires ``ENABLE_SVE_FOR_NS`` to be enabled. When enabling
      ``ENABLE_SVE_FOR_SWD``, a developer must carefully consider whether
      ``CTX_INCLUDE_SVE_REGS`` is also needed.

-  ``ENABLE_STACK_PROTECTOR``: String option to enable the stack protection
   checks in GCC. Allowed values are "all", "strong", "default" and "none". The
   default value is set to "none". "strong" is the recommended stack protection
   level if this feature is desired. "none" disables the stack protection. For
   all values other than "none", the ``plat_get_stack_protector_canary()``
   platform hook needs to be implemented. The value is passed as the last
   component of the option ``-fstack-protector-$ENABLE_STACK_PROTECTOR``.

- ``ENABLE_ERRATA_ALL``: This option is used only for testing purposes, Boolean
   option to enable the workarounds for all errata that TF-A implements. Normally
   they should be explicitly enabled depending on each platform's needs. Not
   recommended for release builds. This option is default set to 0.

-  ``ENCRYPT_BL31``: Binary flag to enable encryption of BL31 firmware. This
   flag depends on ``DECRYPTION_SUPPORT`` build flag.

-  ``ENCRYPT_BL32``: Binary flag to enable encryption of Secure BL32 payload.
   This flag depends on ``DECRYPTION_SUPPORT`` build flag.

-  ``ENC_KEY``: A 32-byte (256-bit) symmetric key in hex string format. It could
   either be SSK or BSSK depending on ``FW_ENC_STATUS`` flag. This value depends
   on ``DECRYPTION_SUPPORT`` build flag.

-  ``ENC_NONCE``: A 12-byte (96-bit) encryption nonce or Initialization Vector
   (IV) in hex string format. This value depends on ``DECRYPTION_SUPPORT``
   build flag.

-  ``ERROR_DEPRECATED``: This option decides whether to treat the usage of
   deprecated platform APIs, helper functions or drivers within Trusted
   Firmware as error. It can take the value 1 (flag the use of deprecated
   APIs as error) or 0. The default is 0.

-  ``ETHOSN_NPU_DRIVER``: boolean option to enable a SiP service that can
   configure an Arm® Ethos™-N NPU. To use this service the target platform's
   ``HW_CONFIG`` must include the device tree nodes for the NPU. Currently, only
   the Arm Juno platform has this included in its ``HW_CONFIG`` and the platform
   only loads the ``HW_CONFIG`` in AArch64 builds. Default is 0.

-  ``ETHOSN_NPU_TZMP1``: boolean option to enable TZMP1 support for the
   Arm® Ethos™-N NPU. Requires ``ETHOSN_NPU_DRIVER`` and
   ``TRUSTED_BOARD_BOOT`` to be enabled.

-  ``ETHOSN_NPU_FW``: location of the NPU firmware binary
   (```ethosn.bin```). This firmware image will be included in the FIP and
   loaded at runtime.

-  ``EL3_EXCEPTION_HANDLING``: When set to ``1``, enable handling of exceptions
   targeted at EL3. When set ``0`` (default), no exceptions are expected or
   handled at EL3, and a panic will result. The exception to this rule is when
   ``SPMD_SPM_AT_SEL2`` is set to ``1``, in which case, only exceptions
   occuring during normal world execution, are trapped to EL3. Any exception
   trapped during secure world execution are trapped to the SPMC. This is
   supported only for AArch64 builds.

-  ``EVENT_LOG_LEVEL``: Chooses the log level to use for Measured Boot when
   ``MEASURED_BOOT`` is enabled. For a list of valid values, see ``LOG_LEVEL``.
   Default value is 40 (LOG_LEVEL_INFO).

-  ``FAULT_INJECTION_SUPPORT``: ARMv8.4 extensions introduced support for fault
   injection from lower ELs, and this build option enables lower ELs to use
   Error Records accessed via System Registers to inject faults. This is
   applicable only to AArch64 builds.

   This feature is intended for testing purposes only, and is advisable to keep
   disabled for production images.

-  ``FIP_NAME``: This is an optional build option which specifies the FIP
   filename for the ``fip`` target. Default is ``fip.bin``.

-  ``FWU_FIP_NAME``: This is an optional build option which specifies the FWU
   FIP filename for the ``fwu_fip`` target. Default is ``fwu_fip.bin``.

-  ``FW_ENC_STATUS``: Top level firmware's encryption numeric flag, values:

   ::

     0: Encryption is done with Secret Symmetric Key (SSK) which is common
        for a class of devices.
     1: Encryption is done with Binding Secret Symmetric Key (BSSK) which is
        unique per device.

   This flag depends on ``DECRYPTION_SUPPORT`` build flag.

-  ``GENERATE_COT``: Boolean flag used to build and execute the ``cert_create``
   tool to create certificates as per the Chain of Trust described in
   :ref:`Trusted Board Boot`. The build system then calls ``fiptool`` to
   include the certificates in the FIP and FWU_FIP. Default value is '0'.

   Specify both ``TRUSTED_BOARD_BOOT=1`` and ``GENERATE_COT=1`` to include support
   for the Trusted Board Boot feature in the BL1 and BL2 images, to generate
   the corresponding certificates, and to include those certificates in the
   FIP and FWU_FIP.

   Note that if ``TRUSTED_BOARD_BOOT=0`` and ``GENERATE_COT=1``, the BL1 and BL2
   images will not include support for Trusted Board Boot. The FIP will still
   include the corresponding certificates. This FIP can be used to verify the
   Chain of Trust on the host machine through other mechanisms.

   Note that if ``TRUSTED_BOARD_BOOT=1`` and ``GENERATE_COT=0``, the BL1 and BL2
   images will include support for Trusted Board Boot, but the FIP and FWU_FIP
   will not include the corresponding certificates, causing a boot failure.

-  ``GICV2_G0_FOR_EL3``: Unlike GICv3, the GICv2 architecture doesn't have
   inherent support for specific EL3 type interrupts. Setting this build option
   to ``1`` assumes GICv2 *Group 0* interrupts are expected to target EL3, both
   by :ref:`platform abstraction layer<platform Interrupt Controller API>` and
   :ref:`Interrupt Management Framework<Interrupt Management Framework>`.
   This allows GICv2 platforms to enable features requiring EL3 interrupt type.
   This also means that all GICv2 Group 0 interrupts are delivered to EL3, and
   the Secure Payload interrupts needs to be synchronously handed over to Secure
   EL1 for handling. The default value of this option is ``0``, which means the
   Group 0 interrupts are assumed to be handled by Secure EL1.

-  ``HANDLE_EA_EL3_FIRST_NS``: When set to ``1``, External Aborts and SError
   Interrupts, resulting from errors in NS world, will be always trapped in
   EL3 i.e. in BL31 at runtime. When set to ``0`` (default), these exceptions
   will be trapped in the current exception level (or in EL1 if the current
   exception level is EL0).

-  ``HW_ASSISTED_COHERENCY``: On most Arm systems to-date, platform-specific
   software operations are required for CPUs to enter and exit coherency.
   However, newer systems exist where CPUs' entry to and exit from coherency
   is managed in hardware. Such systems require software to only initiate these
   operations, and the rest is managed in hardware, minimizing active software
   management. In such systems, this boolean option enables TF-A to carry out
   build and run-time optimizations during boot and power management operations.
   This option defaults to 0 and if it is enabled, then it implies
   ``WARMBOOT_ENABLE_DCACHE_EARLY`` is also enabled.

   If this flag is disabled while the platform which TF-A is compiled for
   includes cores that manage coherency in hardware, then a compilation error is
   generated. This is based on the fact that a system cannot have, at the same
   time, cores that manage coherency in hardware and cores that don't. In other
   words, a platform cannot have, at the same time, cores that require
   ``HW_ASSISTED_COHERENCY=1`` and cores that require
   ``HW_ASSISTED_COHERENCY=0``.

   Note that, when ``HW_ASSISTED_COHERENCY`` is enabled, version 2 of
   translation library (xlat tables v2) must be used; version 1 of translation
   library is not supported.

-  ``IMPDEF_SYSREG_TRAP``: Numeric value to enable the handling traps for
   implementation defined system register accesses from lower ELs. Default
   value is ``0``.

-  ``INVERTED_MEMMAP``: memmap tool print by default lower addresses at the
   bottom, higher addresses at the top. This build flag can be set to '1' to
   invert this behavior. Lower addresses will be printed at the top and higher
   addresses at the bottom.

-  ``INIT_UNUSED_NS_EL2``: This build flag guards code that disables EL2
   safely in scenario where NS-EL2 is present but unused. This flag is set to 0
   by default. Platforms without NS-EL2 in use must enable this flag.

-  ``KEY_ALG``: This build flag enables the user to select the algorithm to be
   used for generating the PKCS keys and subsequent signing of the certificate.
   It accepts 5 values: ``rsa``, ``rsa_1_5``, ``ecdsa``, ``ecdsa-brainpool-regular``
   and ``ecdsa-brainpool-twisted``. The option ``rsa_1_5`` is the legacy PKCS#1
   RSA 1.5 algorithm which is not TBBR compliant and is retained only for
   compatibility. The default value of this flag is ``rsa`` which is the TBBR
   compliant PKCS#1 RSA 2.1 scheme.

-  ``KEY_SIZE``: This build flag enables the user to select the key size for
   the algorithm specified by ``KEY_ALG``. The valid values for ``KEY_SIZE``
   depend on the chosen algorithm and the cryptographic module.

   +---------------------------+------------------------------------+
   |         KEY_ALG           |        Possible key sizes          |
   +===========================+====================================+
   |           rsa             | 1024 , 2048 (default), 3072, 4096  |
   +---------------------------+------------------------------------+
   |          ecdsa            |         256 (default), 384         |
   +---------------------------+------------------------------------+
   |  ecdsa-brainpool-regular  |            256 (default)           |
   +---------------------------+------------------------------------+
   |  ecdsa-brainpool-twisted  |            256 (default)           |
   +---------------------------+------------------------------------+

-  ``HASH_ALG``: This build flag enables the user to select the secure hash
   algorithm. It accepts 3 values: ``sha256``, ``sha384`` and ``sha512``.
   The default value of this flag is ``sha256``.

- ``HW_CONFIG_BASE``: This option specifies the location in memory where the DTB
   should either be loaded by BL2 or can be found by later stages.

-  ``LDFLAGS``: Extra user options appended to the linkers' command line in
   addition to the one set by the build system.

-  ``LOG_LEVEL``: Chooses the log level, which controls the amount of console log
   output compiled into the build. This should be one of the following:

   ::

       0  (LOG_LEVEL_NONE)
       10 (LOG_LEVEL_ERROR)
       20 (LOG_LEVEL_NOTICE)
       30 (LOG_LEVEL_WARNING)
       40 (LOG_LEVEL_INFO)
       50 (LOG_LEVEL_VERBOSE)

   All log output up to and including the selected log level is compiled into
   the build. The default value is 40 in debug builds and 20 in release builds.

-  ``MEASURED_BOOT``: Boolean flag to include support for the Measured Boot
   feature. This flag can be enabled with ``TRUSTED_BOARD_BOOT`` in order to
   provide trust that the code taking the measurements and recording them has
   not been tampered with.

   This option defaults to 0.

-  ``DISCRETE_TPM``: Boolean flag to include support for a Discrete TPM.

   This option defaults to 0.

-  ``TPM_INTERFACE``: When ``DISCRETE_TPM=1``, this is a required flag to
   select the TPM interface. Currently only one interface is supported:

   ::

      FIFO_SPI

-  ``MBOOT_TPM_HASH_ALG``: Build flag to select the TPM hash algorithm used during
   Measured Boot. Currently only accepts ``sha256`` as a valid algorithm.

-  ``MARCH_DIRECTIVE``: used to pass a -march option from the platform build
   options to the compiler. An example usage:

   .. code:: make

      MARCH_DIRECTIVE := -march=armv8.5-a

-  ``HARDEN_SLS``: used to pass -mharden-sls=all from the TF-A build
   options to the compiler currently supporting only of the options.
   GCC documentation:
   https://gcc.gnu.org/onlinedocs/gcc/AArch64-Options.html#index-mharden-sls

   An example usage:

   .. code:: make

      HARDEN_SLS := 1

   This option defaults to 0.

-  ``NON_TRUSTED_WORLD_KEY``: This option is used when ``GENERATE_COT=1``. It
   specifies a file that contains the Non-Trusted World private key in PEM
   format or a PKCS11 URI. If ``SAVE_KEYS=1``, only a file is accepted and it
   will be used to save the key.

-  ``NS_BL2U``: Path to NS_BL2U image in the host file system. This image is
   optional. It is only needed if the platform makefile specifies that it
   is required in order to build the ``fwu_fip`` target.

-  ``NS_TIMER_SWITCH``: Enable save and restore for non-secure timer register
   contents upon world switch. It can take either 0 (don't save and restore) or
   1 (do save and restore). 0 is the default. An SPD may set this to 1 if it
   wants the timer registers to be saved and restored.

-  ``OVERRIDE_LIBC``: This option allows platforms to override the default libc
   for the BL image. It can be either 0 (include) or 1 (remove). The default
   value is 0.

-  ``PL011_GENERIC_UART``: Boolean option to indicate the PL011 driver that
   the underlying hardware is not a full PL011 UART but a minimally compliant
   generic UART, which is a subset of the PL011. The driver will not access
   any register that is not part of the SBSA generic UART specification.
   Default value is 0 (a full PL011 compliant UART is present).

-  ``PLAT``: Choose a platform to build TF-A for. The chosen platform name
   must be subdirectory of any depth under ``plat/``, and must contain a
   platform makefile named ``platform.mk``. For example, to build TF-A for the
   Arm Juno board, select PLAT=juno.

-  ``PLATFORM_REPORT_CTX_MEM_USE``: Reports the context memory allocated for
   each core as well as the global context. The data includes the memory used
   by each world and each privileged exception level. This build option is
   applicable only for ``ARCH=aarch64`` builds. The default value is 0.

-  ``PRELOADED_BL33_BASE``: This option enables booting a preloaded BL33 image
   instead of the normal boot flow. When defined, it must specify the entry
   point address for the preloaded BL33 image. This option is incompatible with
   ``EL3_PAYLOAD_BASE``. If both are defined, ``EL3_PAYLOAD_BASE`` has priority
   over ``PRELOADED_BL33_BASE``.

-  ``PRESERVE_DSU_PMU_REGS``: This options when enabled allows the platform to
   save/restore the DynamIQ Shared Unit's(DSU) Performance Monitoring Unit(PMU)
   registers when the cluster goes through a power cycle. This is disabled by
   default and platforms that require this feature have to enable them.

-  ``PROGRAMMABLE_RESET_ADDRESS``: This option indicates whether the reset
   vector address can be programmed or is fixed on the platform. It can take
   either 0 (fixed) or 1 (programmable). Default is 0. If the platform has a
   programmable reset address, it is expected that a CPU will start executing
   code directly at the right address, both on a cold and warm reset. In this
   case, there is no need to identify the entrypoint on boot and the boot path
   can be optimised. The ``plat_get_my_entrypoint()`` platform porting interface
   does not need to be implemented in this case.

-  ``PSCI_EXTENDED_STATE_ID``: As per PSCI1.0 Specification, there are 2 formats
   possible for the PSCI power-state parameter: original and extended State-ID
   formats. This flag if set to 1, configures the generic PSCI layer to use the
   extended format. The default value of this flag is 0, which means by default
   the original power-state format is used by the PSCI implementation. This flag
   should be specified by the platform makefile and it governs the return value
   of PSCI_FEATURES API for CPU_SUSPEND smc function id. When this option is
   enabled on Arm platforms, the option ``ARM_RECOM_STATE_ID_ENC`` needs to be
   set to 1 as well.

-  ``PSCI_OS_INIT_MODE``: Boolean flag to enable support for optional PSCI
   OS-initiated mode. This option defaults to 0.

-  ``ARCH_FEATURE_AVAILABILITY``: Boolean flag to enable support for the
   optional SMCCC_ARCH_FEATURE_AVAILABILITY call. This option implicitly
   interacts with IMPDEF_SYSREG_TRAP and software emulation. This option
   defaults to 0.

-  ``ENABLE_FEAT_RAS``: Boolean flag to enable Armv8.2 RAS features. RAS features
   are an optional extension for pre-Armv8.2 CPUs, but are mandatory for Armv8.2
   or later CPUs. This flag can take the values 0 or 1. The default value is 0.
   NOTE: This flag enables use of IESB capability to reduce entry latency into
   EL3 even when RAS error handling is not performed on the platform. Hence this
   flag is recommended to be turned on Armv8.2 and later CPUs.

-  ``RESET_TO_BL31``: Enable BL31 entrypoint as the CPU reset vector instead
   of the BL1 entrypoint. It can take the value 0 (CPU reset to BL1
   entrypoint) or 1 (CPU reset to BL31 entrypoint).
   The default value is 0.

-  ``RESET_TO_SP_MIN``: SP_MIN is the minimal AArch32 Secure Payload provided
   in TF-A. This flag configures SP_MIN entrypoint as the CPU reset vector
   instead of the BL1 entrypoint. It can take the value 0 (CPU reset to BL1
   entrypoint) or 1 (CPU reset to SP_MIN entrypoint). The default value is 0.

-  ``RME_GPT_BITLOCK_BLOCK``: This defines the block size (in number of 512MB
-  blocks) covered by a single bit of the bitlock structure during RME GPT
-  operations. The lower the block size, the better opportunity for
-  parallelising GPT operations but at the cost of more bits being needed
-  for the bitlock structure. This numeric parameter can take the values
-  from 0 to 512 and must be a power of 2. The value of 0 is special and
-  and it chooses a single spinlock for all GPT L1 table entries. Default
-  value is 1 which corresponds to block size of 512MB per bit of bitlock
-  structure.

-  ``RME_GPT_MAX_BLOCK``: Numeric value in MB to define the maximum size of
   supported contiguous blocks in GPT Library. This parameter can take the
   values 0, 2, 32 and 512. Setting this value to 0 disables use of Contigious
   descriptors. Default value is 512.

-  ``ROT_KEY``: This option is used when ``GENERATE_COT=1``. It specifies a
   file that contains the ROT private key in PEM format or a PKCS11 URI and
   enforces public key hash generation. If ``SAVE_KEYS=1``, only a file is
   accepted and it will be used to save the key.

-  ``SAVE_KEYS``: This option is used when ``GENERATE_COT=1``. It tells the
   certificate generation tool to save the keys used to establish the Chain of
   Trust. Allowed options are '0' or '1'. Default is '0' (do not save).

-  ``SCP_BL2``: Path to SCP_BL2 image in the host file system. This image is optional.
   If a SCP_BL2 image is present then this option must be passed for the ``fip``
   target.

-  ``SCP_BL2_KEY``: This option is used when ``GENERATE_COT=1``. It specifies a
   file that contains the SCP_BL2 private key in PEM format or a PKCS11 URI.
   If ``SAVE_KEYS=1``, only a file is accepted and it will be used to save the key.

-  ``SCP_BL2U``: Path to SCP_BL2U image in the host file system. This image is
   optional. It is only needed if the platform makefile specifies that it
   is required in order to build the ``fwu_fip`` target.

-  ``SDEI_SUPPORT``: Setting this to ``1`` enables support for Software
   Delegated Exception Interface to BL31 image. This defaults to ``0``.

   When set to ``1``, the build option ``EL3_EXCEPTION_HANDLING`` must also be
   set to ``1``.

-  ``SEPARATE_CODE_AND_RODATA``: Whether code and read-only data should be
   isolated on separate memory pages. This is a trade-off between security and
   memory usage. See "Isolating code and read-only data on separate memory
   pages" section in :ref:`Firmware Design`. This flag is disabled by default
   and affects all BL images.

-  ``SEPARATE_NOBITS_REGION``: Setting this option to ``1`` allows the NOBITS
   sections of BL31 (.bss, stacks, page tables, and coherent memory) to be
   allocated in RAM discontiguous from the loaded firmware image. When set, the
   platform is expected to provide definitions for ``BL31_NOBITS_BASE`` and
   ``BL31_NOBITS_LIMIT``. When the option is ``0`` (the default), NOBITS
   sections are placed in RAM immediately following the loaded firmware image.

-  ``SEPARATE_BL2_NOLOAD_REGION``: Setting this option to ``1`` allows the
   NOLOAD sections of BL2 (.bss, stacks, page tables) to be allocated in RAM
   discontiguous from loaded firmware images. When set, the platform need to
   provide definitions of ``BL2_NOLOAD_START`` and ``BL2_NOLOAD_LIMIT``. This
   flag is disabled by default and NOLOAD sections are placed in RAM immediately
   following the loaded firmware image.

-  ``SEPARATE_SIMD_SECTION``: Setting this option to ``1`` allows the SIMD context
    data structures to be put in a dedicated memory region as decided by platform
    integrator. Default value is ``0`` which means the SIMD context is put in BSS
    section of EL3 firmware.

-  ``SMC_PCI_SUPPORT``: This option allows platforms to handle PCI configuration
   access requests via a standard SMCCC defined in `DEN0115`_. When combined with
   UEFI+ACPI this can provide a certain amount of OS forward compatibility
   with newer platforms that aren't ECAM compliant.

-  ``SPD``: Choose a Secure Payload Dispatcher component to be built into TF-A.
   This build option is only valid if ``ARCH=aarch64``. The value should be
   the path to the directory containing the SPD source, relative to
   ``services/spd/``; the directory is expected to contain a makefile called
   ``<spd-value>.mk``. The SPM Dispatcher standard service is located in
   services/std_svc/spmd and enabled by ``SPD=spmd``. The SPM Dispatcher
   cannot be enabled when the ``SPM_MM`` option is enabled.

-  ``SPIN_ON_BL1_EXIT``: This option introduces an infinite loop in BL1. It can
   take either 0 (no loop) or 1 (add a loop). 0 is the default. This loop stops
   execution in BL1 just before handing over to BL31. At this point, all
   firmware images have been loaded in memory, and the MMU and caches are
   turned off. Refer to the "Debugging options" section for more details.

-  ``SPMC_AT_EL3`` : This boolean option is used jointly with the SPM
   Dispatcher option (``SPD=spmd``). When enabled (1) it indicates the SPMC
   component runs at the EL3 exception level. The default value is ``0`` (
   disabled). This configuration supports pre-Armv8.4 platforms (aka not
   implementing the ``FEAT_SEL2`` extension).

-  ``SPMC_AT_EL3_SEL0_SP`` : Boolean option to enable SEL0 SP load support when
   ``SPMC_AT_EL3`` is enabled. The default value if ``0`` (disabled). This
   option cannot be enabled (``1``) when (``SPMC_AT_EL3``) is disabled.

-  ``SPMC_OPTEE`` : This boolean option is used jointly with the SPM
   Dispatcher option (``SPD=spmd``) and with ``SPMD_SPM_AT_SEL2=0`` to
   indicate that the SPMC at S-EL1 is OP-TEE and an OP-TEE specific loading
   mechanism should be used.

-  ``SPMD_SPM_AT_SEL2`` : This boolean option is used jointly with the SPM
   Dispatcher option (``SPD=spmd``). When enabled (1) it indicates the SPMC
   component runs at the S-EL2 exception level provided by the ``FEAT_SEL2``
   extension. This is the default when enabling the SPM Dispatcher. When
   disabled (0) it indicates the SPMC component runs at the S-EL1 execution
   state or at EL3 if ``SPMC_AT_EL3`` is enabled. The latter configurations
   support pre-Armv8.4 platforms (aka not implementing the ``FEAT_SEL2``
   extension).

-  ``SPM_MM`` : Boolean option to enable the Management Mode (MM)-based Secure
   Partition Manager (SPM) implementation. The default value is ``0``
   (disabled). This option cannot be enabled (``1``) when SPM Dispatcher is
   enabled (``SPD=spmd``).

-  ``SP_LAYOUT_FILE``: Platform provided path to JSON file containing the
   description of secure partitions. The build system will parse this file and
   package all secure partition blobs into the FIP. This file is not
   necessarily part of TF-A tree. Only available when ``SPD=spmd``.

-  ``SP_MIN_WITH_SECURE_FIQ``: Boolean flag to indicate the SP_MIN handles
   secure interrupts (caught through the FIQ line). Platforms can enable
   this directive if they need to handle such interruption. When enabled,
   the FIQ are handled in monitor mode and non secure world is not allowed
   to mask these events. Platforms that enable FIQ handling in SP_MIN shall
   implement the api ``sp_min_plat_fiq_handler()``. The default value is 0.

-  ``SVE_VECTOR_LEN``: SVE vector length to configure in ZCR_EL3.
   Platforms can configure this if they need to lower the hardware
   limit, for example due to asymmetric configuration or limitations of
   software run at lower ELs. The default is the architectural maximum
   of 2048 which should be suitable for most configurations, the
   hardware will limit the effective VL to the maximum physically supported
   VL.

-  ``TRNG_SUPPORT``: Setting this to ``1`` enables support for True
   Random Number Generator Interface to BL31 image. This defaults to ``0``.

-  ``TRUSTED_BOARD_BOOT``: Boolean flag to include support for the Trusted Board
   Boot feature. When set to '1', BL1 and BL2 images include support to load
   and verify the certificates and images in a FIP, and BL1 includes support
   for the Firmware Update. The default value is '0'. Generation and inclusion
   of certificates in the FIP and FWU_FIP depends upon the value of the
   ``GENERATE_COT`` option.

   .. warning::
      This option depends on ``CREATE_KEYS`` to be enabled. If the keys
      already exist in disk, they will be overwritten without further notice.

-  ``TRUSTED_WORLD_KEY``: This option is used when ``GENERATE_COT=1``. It
   specifies a file that contains the Trusted World private key in PEM
   format or a PKCS11 URI. If ``SAVE_KEYS=1``, only a file is accepted and
   it will be used to save the key.

-  ``TSP_INIT_ASYNC``: Choose BL32 initialization method as asynchronous or
   synchronous, (see "Initializing a BL32 Image" section in
   :ref:`Firmware Design`). It can take the value 0 (BL32 is initialized using
   synchronous method) or 1 (BL32 is initialized using asynchronous method).
   Default is 0.

-  ``TSP_NS_INTR_ASYNC_PREEMPT``: A non zero value enables the interrupt
   routing model which routes non-secure interrupts asynchronously from TSP
   to EL3 causing immediate preemption of TSP. The EL3 is responsible
   for saving and restoring the TSP context in this routing model. The
   default routing model (when the value is 0) is to route non-secure
   interrupts to TSP allowing it to save its context and hand over
   synchronously to EL3 via an SMC.

   .. note::
      When ``EL3_EXCEPTION_HANDLING`` is ``1``, ``TSP_NS_INTR_ASYNC_PREEMPT``
      must also be set to ``1``.

-  ``TS_SP_FW_CONFIG``: DTC build flag to include Trusted Services (Crypto and
   internal-trusted-storage) as SP in tb_fw_config device tree.

-  ``TWED_DELAY``: Numeric value to be set in order to delay the trapping of
   WFE instruction. ``ENABLE_FEAT_TWED`` build option must be enabled to set
   this delay. It can take values in the range (0-15). Default value is ``0``
   and based on this value, 2^(TWED_DELAY + 8) cycles will be delayed.
   Platforms need to explicitly update this value based on their requirements.

-  ``USE_ARM_LINK``: This flag determines whether to enable support for ARM
   linker. When the ``LINKER`` build variable points to the armlink linker,
   this flag is enabled automatically. To enable support for armlink, platforms
   will have to provide a scatter file for the BL image. Currently, Tegra
   platforms use the armlink support to compile BL3-1 images.

-  ``USE_COHERENT_MEM``: This flag determines whether to include the coherent
   memory region in the BL memory map or not (see "Use of Coherent memory in
   TF-A" section in :ref:`Firmware Design`). It can take the value 1
   (Coherent memory region is included) or 0 (Coherent memory region is
   excluded). Default is 1.

-  ``USE_KERNEL_DT_CONVENTION``: When this option is enabled, the hardware
   device tree is passed to BL33 using register x0, aligning with the expectations
   of the Linux kernel on Arm platforms. If this option is disabled, a different
   register, typically x1, may be used instead. This build option is
   not necessary when firmware handoff is active (that is, when TRANSFER_LIST=1
   is set), and it will be removed once all platforms have transitioned to that
   convention.

-  ``USE_DSU_DRIVER``: This flag enables DSU (DynamIQ Shared Unit) driver.
   The DSU driver allows save/restore of DSU PMU registers through
   ``PRESERVE_DSU_PMU_REGS`` build option and allows platforms to
   configure powerdown and power settings of DSU.

-  ``ARM_IO_IN_DTB``: This flag determines whether to use IO based on the
   firmware configuration framework. This will move the io_policies into a
   configuration device tree, instead of static structure in the code base.

-  ``COT_DESC_IN_DTB``: This flag determines whether to create COT descriptors
   at runtime using fconf. If this flag is enabled, COT descriptors are
   statically captured in tb_fw_config file in the form of device tree nodes
   and properties. Currently, COT descriptors used by BL2 are moved to the
   device tree and COT descriptors used by BL1 are retained in the code
   base statically.

-  ``SDEI_IN_FCONF``: This flag determines whether to configure SDEI setup in
   runtime using firmware configuration framework. The platform specific SDEI
   shared and private events configuration is retrieved from device tree rather
   than static C structures at compile time. This is only supported if
   SDEI_SUPPORT build flag is enabled.

-  ``SEC_INT_DESC_IN_FCONF``: This flag determines whether to configure Group 0
   and Group1 secure interrupts using the firmware configuration framework. The
   platform specific secure interrupt property descriptor is retrieved from
   device tree in runtime rather than depending on static C structure at compile
   time.

-  ``USE_ROMLIB``: This flag determines whether library at ROM will be used.
   This feature creates a library of functions to be placed in ROM and thus
   reduces SRAM usage. Refer to :ref:`Library at ROM` for further details. Default
   is 0.

-  ``V``: Verbose build. If assigned anything other than 0, the build commands
   are printed. Default is 0.

-  ``VERSION_STRING``: String used in the log output for each TF-A image.
   Defaults to a string formed by concatenating the version number, build type
   and build string.

-  ``W``: Warning level. Some compiler warning options of interest have been
   regrouped and put in the root Makefile. This flag can take the values 0 to 3,
   each level enabling more warning options. Default is 0.

   This option is closely related to the ``E`` option, which enables
   ``-Werror``.

   - ``W=0`` (default)

     Enables a wide assortment of warnings, most notably ``-Wall`` and
     ``-Wextra``, as well as various bad practices and things that are likely to
     result in errors. Includes some compiler specific flags. No warnings are
     expected at this level for any build.

   - ``W=1``

     Enables warnings we want the generic build to include but are too time
     consuming to fix at the moment. It re-enables warnings taken out for
     ``W=0`` builds (a few of the ``-Wextra`` additions). This level is expected
     to eventually be merged into ``W=0``. Some warnings are expected on some
     builds, but new contributions should not introduce new ones.

   - ``W=2`` (recommended)

    Enables warnings we want the generic build to include but cannot be enabled
    due to external libraries. This level is expected to eventually be merged
    into ``W=0``. Lots of warnings are expected, primarily from external
    libraries like zlib and compiler-rt, but new controbutions should not
    introduce new ones.

   - ``W=3``

     Enables warnings that are informative but not necessary and generally too
     verbose and frequently ignored. A very large number of warnings are
     expected.

   The exact set of warning flags depends on the compiler and TF-A warning
   level, however they are all succinctly set in the top-level Makefile. Please
   refer to the `GCC`_ or `Clang`_ documentation for more information on the
   individual flags.

-  ``WARMBOOT_ENABLE_DCACHE_EARLY`` : Boolean option to enable D-cache early on
   the CPU after warm boot. This is applicable for platforms which do not
   require interconnect programming to enable cache coherency (eg: single
   cluster platforms). If this option is enabled, then warm boot path
   enables D-caches immediately after enabling MMU. This option defaults to 0.

-  ``ERRATA_SPECULATIVE_AT``: This flag determines whether to enable ``AT``
   speculative errata workaround or not. It accepts 2 values: ``1`` and ``0``.
   The default value of this flag is ``0``.

   ``AT`` speculative errata workaround disables stage1 page table walk for
   lower ELs (EL1 and EL0) in EL3 so that ``AT`` speculative fetch at any point
   produces either the correct result or failure without TLB allocation.

   This boolean option enables errata for all below CPUs.

   +---------+--------------+-------------------------+
   | Errata  |      CPU     |     Workaround Define   |
   +=========+==============+=========================+
   | 1165522 |  Cortex-A76  |  ``ERRATA_A76_1165522`` |
   +---------+--------------+-------------------------+
   | 1319367 |  Cortex-A72  |  ``ERRATA_A72_1319367`` |
   +---------+--------------+-------------------------+
   | 1319537 |  Cortex-A57  |  ``ERRATA_A57_1319537`` |
   +---------+--------------+-------------------------+
   | 1530923 |  Cortex-A55  |  ``ERRATA_A55_1530923`` |
   +---------+--------------+-------------------------+
   | 1530924 |  Cortex-A53  |  ``ERRATA_A53_1530924`` |
   +---------+--------------+-------------------------+

   .. note::
      This option is enabled by build only if platform sets any of above defines
      mentioned in ’Workaround Define' column in the table.
      If this option is enabled for the EL3 software then EL2 software also must
      implement this workaround due to the behaviour of the errata mentioned
      in new SDEN document which will get published soon.

- ``ERRATA_SME_POWER_DOWN``: Boolean option to disable SME (PSTATE.{ZA,SM}=0)
  before power down and downgrade a suspend to power down request to a normal
  suspend request. This is necessary when software running at lower ELs requests
  power down without first clearing these bits. On affected cores, the CME
  connected to it will reject its power down request. The default value is 0.

- ``RAS_TRAP_NS_ERR_REC_ACCESS``: This flag enables/disables the SCR_EL3.TERR
  bit, to trap access to the RAS ERR and RAS ERX registers from lower ELs.
  This flag is disabled by default.

- ``OPENSSL_DIR``: This option is used to provide the path to a directory on the
  host machine where a custom installation of OpenSSL is located, which is used
  to build the certificate generation, firmware encryption and FIP tools. If
  this option is not set, the default OS installation will be used.

- ``USE_SP804_TIMER``: Use the SP804 timer instead of the Generic Timer for
  functions that wait for an arbitrary time length (udelay and mdelay). The
  default value is 0.

- ``ENABLE_BRBE_FOR_NS``: Numeric value to enable access to the branch record
  buffer registers from NS ELs when FEAT_BRBE is implemented. BRBE is an
  optional architectural feature for AArch64. This flag can take the values
  0 to 2, to align with the ``ENABLE_FEAT`` mechanism. The default is 0
  and it is automatically disabled when the target architecture is AArch32.

- ``ENABLE_TRBE_FOR_NS``: Numeric value to enable access of trace buffer
  control registers from NS ELs, NS-EL2 or NS-EL1(when NS-EL2 is implemented
  but unused) when FEAT_TRBE is implemented. TRBE is an optional architectural
  feature for AArch64. This flag can take the values  0 to 2, to align with the
  ``ENABLE_FEAT`` mechanism. The default is 0 and it is automatically
  disabled when the target architecture is AArch32.

- ``ENABLE_SYS_REG_TRACE_FOR_NS``: Numeric value to enable trace system
  registers access from NS ELs, NS-EL2 or NS-EL1 (when NS-EL2 is implemented
  but unused). This feature is available if trace unit such as ETMv4.x, and
  ETE(extending ETM feature) is implemented. This flag can take the values
  0 to 2, to align with the ``ENABLE_FEAT`` mechanism. The default is 0.

- ``ENABLE_TRF_FOR_NS``: Numeric value to enable trace filter control registers
  access from NS ELs, NS-EL2 or NS-EL1 (when NS-EL2 is implemented but unused),
  if FEAT_TRF is implemented. This flag can take the values 0 to 2, to align
  with the ``ENABLE_FEAT`` mechanism. This flag is disabled by default.

- ``CONDITIONAL_CMO``: Boolean option to enable call to platform-defined routine
  ``plat_can_cmo`` which will return zero if cache management operations should
  be skipped and non-zero otherwise. By default, this option is disabled which
  means platform hook won't be checked and CMOs will always be performed when
  related functions are called.

- ``ERRATA_ABI_SUPPORT``: Boolean option to enable support for Errata management
  firmware interface for the BL31 image. By default its disabled (``0``).

- ``ERRATA_NON_ARM_INTERCONNECT``: Boolean option to enable support for the
  errata mitigation for platforms with a non-arm interconnect using the errata
  ABI. By default its disabled (``0``).

- ``ENABLE_CONSOLE_GETC``: Boolean option to enable `getc()` feature in console
  driver(s). By default it is disabled (``0``) because it constitutes an attack
  vector into TF-A by potentially allowing an attacker to inject arbitrary data.
  This option should only be enabled on a need basis if there is a use case for
  reading characters from the console.

GIC driver options
--------------------

The generic GIC driver can be included with the ``USE_GIC_DRIVER`` option. It is
a numeric option that can take the following values:

 - ``0``: generic GIC driver not enabled. Any support is entirely in platform
   code. Strongly discouraged for GIC based interrupt controllers.

 - ``1``: enable the use of the generic GIC driver but do not include any files
   or function definitions. It is then the platform's responsibility to provide
   these. This is useful if the platform either has a custom GIC implementation
   or an alternative interrupt controller design. Use of this option is strongly
   discouraged for standard GIC implementations.

 - ``2``: use the GICv2 driver

 - ``3``: use the GICv3 driver. See the next section on how to further configure
   it. Use this option for GICv4 implementations. Requires calling
   ``gic_set_gicr_frames()``.

 - ``5``: use the EXPERIMENTAL GICv5 driver. Requires ``ENABLE_FEAT_GCIE=1``.

 For GIC driver versions other than ``1``, deciding when to save and restore GIC
 context on a power domain state transition, as well as any GIC actions outside
 of the PSCI library's visibility are the platform's responsibility. The driver
 provides implementations of all necessary subroutines, they only need to be
 called as appropriate.

GICv3 driver options
~~~~~~~~~~~~~~~~~~~~

``USE_GIC_DRIVER=3`` is the preferred way of including GICv3 driver files. The
old (deprecated) way of included them is using the directive:
``include drivers/arm/gic/v3/gicv3.mk``

The driver can be configured with the following options set in the platform
makefile:

-  ``GICV3_SUPPORT_GIC600``: Add support for the GIC-600 variants of GICv3.
   Enabling this option will add runtime detection support for the
   GIC-600, so is safe to select even for a GIC500 implementation.
   This option defaults to 0.

- ``GICV3_SUPPORT_GIC600AE_FMU``: Add support for the Fault Management Unit
   for GIC-600 AE. Enabling this option will introduce support to initialize
   the FMU. Platforms should call the init function during boot to enable the
   FMU and its safety mechanisms. This option defaults to 0.

-  ``GICV3_IMPL_GIC600_MULTICHIP``: Selects GIC-600 variant with multichip
   functionality. This option defaults to 0

-  ``GICV3_OVERRIDE_DISTIF_PWR_OPS``: Allows override of default implementation
   of ``arm_gicv3_distif_pre_save`` and ``arm_gicv3_distif_post_restore``
   functions. This is required for FVP platform which need to simulate GIC save
   and restore during SYSTEM_SUSPEND without powering down GIC. Default is 0.

-  ``GIC_ENABLE_V4_EXTN`` : Enables GICv4 related changes in GICv3 driver.
   This option defaults to 0.

-  ``GIC_EXT_INTID``: When set to ``1``, GICv3 driver will support extended
   PPI (1056-1119) and SPI (4096-5119) range. This option defaults to 0.

Debugging options
-----------------

To compile a debug version and make the build more verbose use

.. code:: shell

    make PLAT=<platform> DEBUG=1 V=1 all

AArch64 GCC 11 uses DWARF version 5 debugging symbols by default. Some tools
(for example Arm-DS) might not support this and may need an older version of
DWARF symbols to be emitted by GCC. This can be achieved by using the
``-gdwarf-<version>`` flag, with the version being set to 2, 3, 4 or 5. Setting
the version to 4 is recommended for Arm-DS.

When debugging logic problems it might also be useful to disable all compiler
optimizations by using ``-O0``.

.. warning::
   Using ``-O0`` could cause output images to be larger and base addresses
   might need to be recalculated (see the **Memory layout on Arm development
   platforms** section in the :ref:`Firmware Design`).

Extra debug options can be passed to the build system by setting ``CFLAGS`` or
``LDFLAGS``:

.. code:: shell

    CFLAGS='-O0 -gdwarf-2'                                     \
    make PLAT=<platform> DEBUG=1 V=1 all

Note that using ``-Wl,`` style compilation driver options in ``CFLAGS`` will be
ignored as the linker is called directly.

It is also possible to introduce an infinite loop to help in debugging the
post-BL2 phase of TF-A. This can be done by rebuilding BL1 with the
``SPIN_ON_BL1_EXIT=1`` build flag. Refer to the :ref:`build_options_common`
section. In this case, the developer may take control of the target using a
debugger when indicated by the console output. When using Arm-DS, the following
commands can be used:

::

    # Stop target execution
    interrupt

    #
    # Prepare your debugging environment, e.g. set breakpoints
    #

    # Jump over the debug loop
    set var $AARCH64::$Core::$PC = $AARCH64::$Core::$PC + 4

    # Resume execution
    continue

.. _build_options_experimental:

Experimental build options
---------------------------

Common build options
~~~~~~~~~~~~~~~~~~~~

-  ``DICE_PROTECTION_ENVIRONMENT``: Boolean flag to specify the measured boot
   backend when ``MEASURED_BOOT`` is enabled. The default value is ``0``. When
   set to ``1`` then measurements and additional metadata collected during the
   measured boot process are sent to the DICE Protection Environment for storage
   and processing. A certificate chain, which represents the boot state of the
   device, can be queried from the DPE.

-  ``DRTM_SUPPORT``: Boolean flag to enable support for Dynamic Root of Trust
   for Measurement (DRTM). This feature has trust dependency on BL31 for taking
   the measurements and recording them as per `PSA DRTM specification`_. For
   platforms which use BL2 to load/authenticate BL31 ``TRUSTED_BOARD_BOOT`` can
   be used and for the platforms which use ``RESET_TO_BL31`` platform owners
   should have mechanism to authenticate BL31. This option defaults to 0.

-  ``ENABLE_RME``: Numeric value to enable support for the ARMv9 Realm
   Management Extension. This flag can take the values 0 to 2, to align with
   the ``ENABLE_FEAT`` mechanism. Default value is 0.

-  ``ENABLE_FEAT_MEC``: Numeric value to enable support for the ARMv9.2 Memory
   Encryption Contexts (MEC). This flag can take the values 0 to 2, to align
   with the ``ENABLE_FEAT`` mechanism. MEC supports multiple encryption
   contexts for Realm security state and only one encryption context for the
   rest of the security states. Default value is 0.

-  ``RMMD_ENABLE_EL3_TOKEN_SIGN``: Numeric value to enable support for singing
   realm attestation token signing requests in EL3. This flag can take the
   values 0 and 1. The default value is ``0``. When set to ``1``, this option
   enables additional RMMD SMCs to push and pop requests for signing to
   EL3 along with platform hooks that must be implemented to service those
   requests and responses.

-  ``ENABLE_SME_FOR_NS``: Numeric value to enable Scalable Matrix Extension
   (SME), SVE, and FPU/SIMD for the non-secure world only. These features share
   registers so are enabled together. Using this option without
   ENABLE_SME_FOR_SWD=1 will cause SME, SVE, and FPU/SIMD instructions in secure
   world to trap to EL3. Requires ``ENABLE_SVE_FOR_NS`` to be set as SME is a
   superset of SVE. SME is an optional architectural feature for AArch64.
   At this time, this build option cannot be used on systems that have
   SPD=spmd/SPM_MM and atempting to build with this option will fail.
   This flag can take the values 0 to 2, to align with the ``ENABLE_FEAT``
   mechanism. Default is 0.

-  ``ENABLE_SME2_FOR_NS``: Numeric value to enable Scalable Matrix Extension
   version 2 (SME2) for the non-secure world only. SME2 is an optional
   architectural feature for AArch64.
   This should be set along with ENABLE_SME_FOR_NS=1, if not, the default SME
   accesses will still be trapped. This flag can take the values 0 to 2, to
   align with the ``ENABLE_FEAT`` mechanism. Default is 0.

-  ``ENABLE_SME_FOR_SWD``: Boolean option to enable the Scalable Matrix
   Extension for secure world. Used along with SVE and FPU/SIMD.
   ENABLE_SME_FOR_NS and ENABLE_SVE_FOR_SWD must also be set to use this.
   Default is 0.

-  ``ENABLE_SPMD_LP`` : This boolean option is used jointly with the SPM
   Dispatcher option (``SPD=spmd``). When enabled (1) it indicates support
   for logical partitions in EL3, managed by the SPMD as defined in the
   FF-A v1.2 specification. This flag is disabled by default. This flag
   must not be used if ``SPMC_AT_EL3`` is enabled.

-  ``FEATURE_DETECTION``: Boolean option to enable the architectural features
   verification mechanism. This is a debug feature that compares the
   architectural features enabled through the feature specific build flags
   (ENABLE_FEAT_xxx) with the features actually available on the CPU running,
   and reports any discrepancies.
   This flag will also enable errata ordering checking for ``DEBUG`` builds.

   It is expected that this feature is only used for flexible platforms like
   software emulators, or for hardware platforms at bringup time, to verify
   that the configured feature set matches the CPU.
   The ``FEATURE_DETECTION`` macro is disabled by default.

-  ``PSA_CRYPTO``: Boolean option for enabling MbedTLS PSA crypto APIs support.
   The platform will use PSA compliant Crypto APIs during authentication and
   image measurement process by enabling this option. It uses APIs defined as
   per the `PSA Crypto API specification`_. This feature is only supported if
   using MbedTLS 3.x version. It is disabled (``0``) by default.

-  ``LFA_SUPPORT``: Boolean flag to enable support for Live Firmware
   activation as per the specification. This option defaults to 0.

-  ``TRANSFER_LIST``: Setting this to ``1`` enables support for Firmware
   Handoff using Transfer List defined in `Firmware Handoff specification`_.
   This defaults to ``0``. Current implementation follows the Firmware Handoff
   specification v0.9.

-  ``USE_DEBUGFS``: When set to 1 this option exposes a virtual filesystem
   interface through BL31 as a SiP SMC function.
   Default is disabled (0).

-  ``HOB_LIST``: Setting this to ``1`` enables support for passing boot
   information using HOB defined in `Platform Initialization specification`_.
   This defaults to ``0``.

-  ``ENABLE_ACS_SMC``: When set to ``1``, this enables support for ACS SMC
   handler code to handle SMC calls from the Architecture Compliance Suite. The
   handler is intentionally empty to reserve the SMC section and allow
   project-specific implementations in future ACS use cases.

Firmware update options
~~~~~~~~~~~~~~~~~~~~~~~

-  ``PSA_FWU_SUPPORT``: Enable the firmware update mechanism as per the
   `PSA FW update specification`_. The default value is 0.
   PSA firmware update implementation has few limitations, such as:

   -  BL2 is not part of the protocol-updatable images. If BL2 needs to
      be updated, then it should be done through another platform-defined
      mechanism.

   -  It assumes the platform's hardware supports CRC32 instructions.

-  ``NR_OF_FW_BANKS``: Define the number of firmware banks. This flag is used
   in defining the firmware update metadata structure. This flag is by default
   set to '2'.

-  ``NR_OF_IMAGES_IN_FW_BANK``: Define the number of firmware images in each
   firmware bank. Each firmware bank must have the same number of images as per
   the `PSA FW update specification`_.
   This flag is used in defining the firmware update metadata structure. This
   flag is by default set to '1'.

- ``PSA_FWU_METADATA_FW_STORE_DESC``: To be enabled when the FWU
   metadata contains image description. The default value is 1.

   The version 2 of the FWU metadata allows for an opaque metadata
   structure where a platform can choose to not include the firmware
   store description in the metadata structure. This option indicates
   if the firmware store description, which provides information on
   the updatable images is part of the structure.

--------------

*Copyright (c) 2019-2025, Arm Limited. All rights reserved.*

.. _DEN0115: https://developer.arm.com/docs/den0115/latest
.. _PSA FW update specification: https://developer.arm.com/documentation/den0118/latest/
.. _PSA DRTM specification: https://developer.arm.com/documentation/den0113/a
.. _GCC: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
.. _Clang: https://clang.llvm.org/docs/DiagnosticsReference.html
.. _Firmware Handoff specification: https://github.com/FirmwareHandoff/firmware_handoff/releases/tag/v0.9
.. _PSA Crypto API specification: https://armmbed.github.io/mbed-crypto/html/
.. _Platform Initialization specification: https://uefi.org/specs/PI/1.8/index.html
.. _TF-A public mailing list: https://lists.trustedfirmware.org/mailman3/lists/tf-a.lists.trustedfirmware.org/