forked from brl/citadel
101 lines
4.6 KiB
Plaintext
101 lines
4.6 KiB
Plaintext
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2012/03/30 - Mark Hatle <mark.hatle@windriver.com>
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- Initial Revision
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Introduction
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============
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The individual CPU, and ABI tunings are contained in this directory. A
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number of local and global variables are used to control the way the
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tunings are setup and how they work together to specify an optimized
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configuration.
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The following is brief summary of the generic components that are used
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in these tunings.
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AVAILTUNES - This is a list of all of the tuning definitions currently
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available in the system. Not all tunes in this list may be compatible
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with the machine configuration, or each other in a multilib
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configuration. Each tuning file can add to this list using "+=", but
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should never replace the list using "=".
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DEFAULTTUNE - This specifies the tune to use for a particular build.
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Each tune should specify a reasonable default, which can be overriden by
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a machine or multilib configuration. The specified tune must be listed
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in the AVAILTUNES.
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TUNEVALID[feature] - The <feature> is defined with a human readable
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explanation for what it does. All architectural, cpu, abi, etc tuning
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features must be defined using TUNEVALID.
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TUNECONFLICTS[feature] - A list of features which conflict with <feature>.
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New sanity checks will try to reject combinations in which a single
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tuning ends up with features which conflict with each other.
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TUNE_FEATURES - This is automatically defined as TUNE_FEATURES_tune-<tune>.
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See TUNE_FEATURES_tune-<tune> for more information.
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TUNE_FEATURES_tune-<tune> - Specify the features used to describe a
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specific tune. This is a list of features that a tune support, each
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feature must be in the TUNEVALID list. Note: the tune and a given
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feature name may be the same, but they have different purposes. Only
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features may be used to change behavior, while tunes are used to
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describe an overall set of features.
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ABIEXTENSION - An ABI extension may be specified by a specific feature
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or other tuning setting, such as TARGET_FPU. Any ABI extensions either
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need to be defined in the architectures base arch file, i.e.
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ABIEXTENSION = "eabi" in the arm case, or appended to in specific tune
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files with a ".=". Spaces are not allowed in this variable.
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TUNE_CCARGS - Setup the cflags based on the TUNE_FEATURES settings.
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These should be additive when defined using "+=". All items in this
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list should be dynamic! i.e.
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${@bb.utils.contains("TUNE_FEATURES", "feature", "cflag", "!cflag", d)}
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TUNE_ARCH - The GNU canonical arch for a specific architecture. i.e.
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arm, armeb, mips, mips64, etc. This value is used by bitbake to setup
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configure. TUNE_ARCH definitions are specific to a given architecture.
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They may be a single static definition, or may be dynamically adjusted.
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See each architecture's README for details for that CPU family.
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TUNE_PKGARCH - The package architecture used by the packaging systems to
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define the architecture, abi and tuning of a particular package.
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Similarly to TUNE_ARCH, the definition of TUNE_PKGARCH is specific to
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each architecture. See each architectures README for details for that
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CPU family.
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PACKAGE_EXTRA_ARCHS - Lists all runtime compatible package
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architectures. By default this is equal to
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PACKAGE_EXTRA_ARCHS_tune-<tune>. If an architecture deviates from the
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default it will be listed in the architecture README.
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PACKAGE_EXTRA_ARCHS_tune-<tune> - List all of the package architectures
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that are compatible with this specific tune. The package arch of this
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tune must be in the list.
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TARGET_FPU - The FPU setting for a given tune, hard (generate floating
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point instructions), soft (generate internal gcc calls), "other"
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architecture specific floating point. This is synchronized with the
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compiler and other toolchain items. This should be dynamically
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configured in the same way that TUNE_CCARGS is.
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BASE_LIB_tune-<tune> - The "/lib" location for a specific ABI. This is
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used in a multilib configuration to place the libraries in the correct,
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non-conflicting locations.
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Best Practice
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=============
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The tune infrastructure is designed to be hierarchical. When writing a
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new tune file for a "fast-forward" CPU architecture (one that supports
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everything from a previous generation), it is recommended to require the
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previous generation tune file and specify PACKAGE_EXTRA_ARCHS using the
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previous generation's override and appending the new tune. Note that
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only one previous tune file should be included to avoid mutiple includes
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of the base arch which could lead to a broken configuration due to
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multiple prepend and append assignments.
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For example, for x86, there is a common x86/arch-x86.inc which is
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included in the base i586 tune file. The core2 tune builds
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on that, and corei7 builds on core2.
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