doc: Split the User Guide into multiple files
The User Guide document has grown organically over time and
now covers a wide range of topics, making it difficult to
skim read and extract information from. Currently, it covers
these topics and maybe a couple more:
- Requirements (hardware, tools, libs)
- Checking out the repo
- Basic build instructions
- A comprehensive list of build flags
- FIP packaging
- Building specifically for Juno
- Firmware update images
- EL3 payloads
- Preloaded BL33 boot flow
- Running on FVPs
- Running on Juno
I have separated these out into a few groups that become new
documents. Broadly speaking, build instructions for the tools,
for TF-A generally, and for specific scenarios are separated.
Content relating to specific platforms (Juno and the FVPs are
Arm-specific platforms, essentially) has been moved into the
documentation that is specific to those platforms, under
docs/plat/arm.
Change-Id: Ica87c52d8cd4f577332be0b0738998ea3ba3bbec
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
new file mode 100644
index 0000000..fded1e0
--- /dev/null
+++ b/docs/getting_started/build-options.rst
@@ -0,0 +1,623 @@
+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``.
+
+- ``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_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`.
+
+- ``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.
+
+- ``BL2_AT_EL3``: This is an optional build option that enables the use of
+ BL2 at EL3 execution level.
+
+- ``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 BL2_AT_EL3
+ 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 the
+ file that contains the BL31 private key in PEM format. If ``SAVE_KEYS=1``,
+ this file name 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 the
+ file that contains the BL32 private key in PEM format. If ``SAVE_KEYS=1``,
+ this file name will be used to save the key.
+
+- ``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 the
+ file that contains the BL33 private key in PEM format. If ``SAVE_KEYS=1``,
+ this file name 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``. Selects the branch protection features to use:
+- 0: Default value turns off all types of branch protection
+- 1: Enables all types of branch protection features
+- 2: Return address signing to its standard level
+- 3: Extend the signing to include leaf functions
+
+ 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 |
+ +-------+--------------+-------+-----+
+
+ This option defaults to 0 and this is an experimental feature.
+ 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.
+
+- ``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.
+
+- ``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_PAUTH_REGS``: Boolean option that, when set to 1, enables
+ 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. Default value is 0 and this is an experimental feature.
+ Note that Pointer Authentication is enabled for Non-secure world irrespective
+ of the value of this flag if the CPU supports it.
+
+- ``DEBUG``: Chooses between a debug and release build. It can take either 0
+ (release) or 1 (debug) as values. 0 is the default.
+
+- ``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.
+
+- ``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.
+
+- ``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``: Boolean option to enable Activity Monitor Unit extensions.
+ 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. 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 enables 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_MPAM_FOR_LOWER_ELS``: Boolean option 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.
+
+ When this option is set to ``1``, 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 ``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 BL31. 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_LOWER_ELS`` : Boolean option to enable Statistical Profiling
+ extensions. This is an optional architectural feature for AArch64.
+ The default is 1 but is automatically disabled when the target architecture
+ is AArch32.
+
+- ``ENABLE_SPM`` : Boolean option to enable the Secure Partition Manager (SPM).
+ Refer to :ref:`Secure Partition Manager` for more details about
+ this feature. Default is 0.
+
+- ``ENABLE_SVE_FOR_NS``: Boolean option to enable Scalable Vector Extension
+ (SVE) for the Non-secure world only. SVE is an optional architectural feature
+ for AArch64. Note that when SVE is enabled for the Non-secure world, access
+ to SIMD and floating-point functionality from the Secure world is disabled.
+ This is to avoid corruption of the Non-secure world data in the Z-registers
+ which are aliased by the SIMD and FP registers. The build option is not
+ compatible with the ``CTX_INCLUDE_FPREGS`` build option, and will raise an
+ assert on platforms where SVE is implemented and ``ENABLE_SVE_FOR_NS`` set to
+ 1. The default is 1 but is automatically disabled when the target
+ architecture is AArch32.
+
+- ``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``.
+
+- ``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.
+
+- ``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. This is supported only for AArch64
+ builds.
+
+- ``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``.
+
+- ``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 `platform abstraction layer`__ and `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.
+
+ .. __: `platform-interrupt-controller-API.rst`
+ .. __: `interrupt-framework-design.rst`
+
+- ``HANDLE_EA_EL3_FIRST``: When set to ``1``, External Aborts and SError
+ Interrupts 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.
+
+- ``JUNO_AARCH32_EL3_RUNTIME``: This build flag enables you to execute EL3
+ runtime software in AArch32 mode, which is required to run AArch32 on Juno.
+ By default this flag is set to '0'. Enabling this flag builds BL1 and BL2 in
+ AArch64 and facilitates the loading of ``SP_MIN`` and BL33 as AArch32 executable
+ images.
+
+- ``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 3 values: ``rsa``, ``rsa_1_5`` and ``ecdsa``. 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.
+
+- ``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``.
+
+- ``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.
+
+- ``NON_TRUSTED_WORLD_KEY``: This option is used when ``GENERATE_COT=1``. It
+ specifies the file that contains the Non-Trusted World private key in PEM
+ format. If ``SAVE_KEYS=1``, this file name 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.
+
+- ``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``.
+
+- ``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.
+
+- ``RAS_EXTENSION``: When set to ``1``, 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.
+
+ When ``RAS_EXTENSION`` is set to ``1``, ``HANDLE_EA_EL3_FIRST`` must also be
+ set to ``1``.
+
+ This option is disabled by default.
+
+- ``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.
+
+- ``ROT_KEY``: This option is used when ``GENERATE_COT=1``. It specifies the
+ file that contains the ROT private key in PEM format. If ``SAVE_KEYS=1``, this
+ file name 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 the
+ file that contains the SCP_BL2 private key in PEM format. If ``SAVE_KEYS=1``,
+ this file name 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.
+
+- ``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``.
+
+- ``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.
+
+- ``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.
+
+- ``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 the file that contains the Trusted World private key in PEM
+ format. If ``SAVE_KEYS=1``, this file name 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``.
+
+- ``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_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.
+
+- ``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.
+
+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 uses DWARF version 4 debugging symbols by default. Some tools (for
+example DS-5) 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 or 3. Setting the
+version to 2 is recommended for DS-5 versions older than 5.16.
+
+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 DS-5, 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
+
+--------------
+
+*Copyright (c) 2019, Arm Limited. All rights reserved.*