make_helpers/toolchain.mk - filogic/atf - Gitiles

 #
 # Copyright (c) 2023-2024, Arm Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #

 #
 # TF-A uses three toolchains:
 #
 #   - The host toolchain (`host`) for building native tools
 #   - The AArch32 toolchain (`aarch32`) for building Arm AArch32 images
 #   - The AArch64 toolchain (`aarch64`) for building Arm AArch64 images
 #
 # In the main Makefile only one of the two Arm toolchains is enabled in any
 # given build, but individual tools and libraries may need access to both.
 #

 toolchains ?= host $(ARCH)

 ifneq ($(filter host,$(toolchains)),)
         host-cc := $(HOSTCC)
         host-cpp := $(HOSTCPP)

         host-as := $(HOSTAS)

         host-ld := $(HOSTLD)
         host-oc := $(HOSTOC)
         host-od := $(HOSTOD)
         host-ar := $(HOSTAR)

         host-dtc := $(HOSTDTC)
 endif

 ifneq ($(filter aarch32,$(toolchains)),)
         aarch32-cc := $(if $(filter-out default,$(origin CC)),$(CC))
         aarch32-cpp := $(if $(filter-out default,$(origin CPP)),$(CPP))

         aarch32-as := $(if $(filter-out default,$(origin AS)),$(AS))

         aarch32-ld := $(if $(filter-out default,$(origin LD)),$(LD))
         aarch32-oc := $(if $(filter-out default,$(origin OC)),$(OC))
         aarch32-od := $(if $(filter-out default,$(origin OD)),$(OD))
         aarch32-ar := $(if $(filter-out default,$(origin AR)),$(AR))

         aarch32-dtc := $(if $(filter-out default,$(origin DTC)),$(DTC))
 endif

 ifneq ($(filter aarch64,$(toolchains)),)
         aarch64-cc := $(if $(filter-out default,$(origin CC)),$(CC))
         aarch64-cpp := $(if $(filter-out default,$(origin CPP)),$(CPP))

         aarch64-as := $(if $(filter-out default,$(origin AS)),$(AS))

         aarch64-ld := $(if $(filter-out default,$(origin LD)),$(LD))
         aarch64-oc := $(if $(filter-out default,$(origin OC)),$(OC))
         aarch64-od := $(if $(filter-out default,$(origin OD)),$(OD))
         aarch64-ar := $(if $(filter-out default,$(origin AR)),$(AR))

         aarch64-dtc := $(if $(filter-out default,$(origin DTC)),$(DTC))
 endif

 include $(dir $(lastword $(MAKEFILE_LIST)))build_env.mk
 include $(addprefix $(dir $(lastword $(MAKEFILE_LIST)))toolchains/, \
         $(addsuffix .mk,$(toolchains)))

 #
 # Configure tool classes that we recognize.
 #
 # In the context of this build system, a tool class identifies a specific role
 # or type of tool in the toolchain.
 #

 # C-related tools
 tool-classes := cc # C compilers
 tool-classes += cpp # C preprocessors

 # Assembly-related tools
 tool-classes += as # Assemblers

 # Linking and object-handling tools
 tool-classes += ld # Linkers
 tool-classes += oc # Object copiers
 tool-classes += od # Object dumpers
 tool-classes += ar # Archivers

 # Other tools
 tool-classes += dtc # Device tree compilers

 #
 # Configure tools that we recognize.
 #
 # Here we declare the list of specific toolchain tools that we know how to
 # interact with. We don't organize these into tool classes yet - that happens
 # further down.
 #

 # Arm Compiler for Embedded
 tools := arm-clang # armclang
 tools += arm-link # armlink
 tools += arm-ar # armar
 tools += arm-fromelf # fromelf

 # LLVM Project
 tools += llvm-clang # clang
 tools += llvm-lld # lld
 tools += llvm-objcopy # llvm-objcopy
 tools += llvm-objdump # llvm-objdump
 tools += llvm-ar # llvm-ar

 # GNU Compiler Collection & GNU Binary Utilities
 tools += gnu-gcc # gcc
 tools += gnu-ld # ld
 tools += gnu-objcopy # objcopy
 tools += gnu-objdump # objdump
 tools += gnu-ar # gcc-ar

 # Other tools
 tools += dtc # Device Tree Compiler

 #
 # Assign tools to tool classes.
 #
 # Multifunctional tools, i.e. tools which can perform multiple roles in a
 # toolchain, may be specified in multiple tool class lists. For example, a C
 # compiler which can also perform the role of a linker may be placed in both
 # `tools-cc` and `tools-ld`.
 #

 # C-related tools
 tools-cc := arm-clang llvm-clang gnu-gcc # C compilers
 tools-cpp := arm-clang llvm-clang gnu-gcc # C preprocessors

 # Assembly-related tools
 tools-as := arm-clang llvm-clang gnu-gcc # Assemblers

 # Linking and object-handling tools
 tools-ld := arm-clang arm-link llvm-clang llvm-lld gnu-gcc gnu-ld # Linkers
 tools-oc := arm-fromelf llvm-objcopy gnu-objcopy # Object copiers
 tools-od := arm-fromelf llvm-objdump gnu-objdump # Object dumpers
 tools-ar := arm-ar llvm-ar gnu-ar # Archivers

 # Other tools
 tools-dtc := dtc # Device tree compilers

 define check-tool-class-tools
         $(eval tool-class := $(1))

         ifndef tools-$(tool-class)
                 $$(error no tools registered to handle tool class `$(tool-class)`)
         endif
 endef

 $(foreach tool-class,$(tool-classes), \
         $(eval $(call check-tool-class-tools,$(tool-class))))

 #
 # Default tools for each toolchain.
 #
 # Toolchains can specify a default path to any given tool with a tool class.
 # These values are used in the absence of user-specified values, and are
 # configured by the makefile for each toolchain using variables of the form:
 #
 #   - $(toolchain)-$(tool-class)-default
 #
 # For example, the default C compiler for the AArch32 and AArch64 toolchains
 # could be configured with:
 #
 #   - aarch32-cc-default
 #   - aarch64-cc-default
 #

 define check-toolchain-tool-class-default
         $(eval toolchain := $(1))
         $(eval tool-class := $(2))

         ifndef $(toolchain)-$(tool-class)-default
                 $$(error no default value specified for tool class `$(tool-class)` of toolchain `$(toolchain)`)
         endif
 endef

 define check-toolchain-tool-class-defaults
         $(eval toolchain := $(1))

         $(foreach tool-class,$(tool-classes), \
                 $(eval $(call check-toolchain-tool-class-default,$(toolchain),$(tool-class))))
 endef

 $(foreach toolchain,$(toolchains), \
         $(eval $(call check-toolchain-tool-class-defaults,$(toolchain))))

 #
 # Helper functions to identify toolchain tools.
 #
 # The functions defined in this section return a tool identifier when given a
 # path to a binary. We generally check a help or version string to more reliably
 # identify tools than by looking at the path alone (e.g. `gcc` on macOS is
 # actually Apple Clang).
 #
 # Each tool-guessing function (`guess-tool-$(tool)`) takes a single argument
 # giving the path to the tool to guess, and returns a non-empty value if the
 # tool corresponds to the tool identifier `$(tool)`:
 #
 #     $(call guess-tool-llvm-clang,aarch64-none-elf-gcc) # <empty>
 #     $(call guess-tool-gnu-gcc,aarch64-none-elf-gcc) # <non-empty>
 #
 # The `guess-tool` function tries to find the corresponding tool identifier
 # for a tool given its path. It takes two arguments:
 #
 #   - $(1): a list of candidate tool identifiers to check
 #   - $(2): the path to the tool to identify
 #
 # If any of the guess functions corresponding to candidate tool identifiers
 # return a non-empty value then the tool identifier of the first function to do
 # so is returned:
 #
 #     $(call guess-tool,gnu-gcc llvm-clang,armclang) # <empty>
 #     $(call guess-tool,gnu-gcc llvm-clang,clang-14) # llvm-clang
 #     $(call guess-tool,gnu-gcc llvm-clang,aarch64-none-elf-gcc-12) # gnu-gcc
 #
 # Tools are checked in the order that they appear in `tools-$(tool-class)`, and
 # the first match is returned.
 #

 # Arm Compiler for Embedded
 guess-tool-arm-clang = $(shell $(1) --version 2>&1 | grep -o "Tool: armclang")
 guess-tool-arm-link = $(shell $(1) --help 2>&1 | grep -o "Tool: armlink")
 guess-tool-arm-fromelf = $(shell $(1) --help 2>&1 | grep -o "Tool: fromelf")
 guess-tool-arm-ar = $(shell $(1) --version 2>&1 | grep -o "Tool: armar")

 # LLVM Project
 guess-tool-llvm-clang = $(shell $(1) -v 2>&1 | grep -o "clang version")
 guess-tool-llvm-lld = $(shell $(1) --help 2>&1 | grep -o "OVERVIEW: lld")
 guess-tool-llvm-objcopy = $(shell $(1) --help 2>&1 | grep -o "llvm-objcopy tool")
 guess-tool-llvm-objdump = $(shell $(1) --help 2>&1 | grep -o "llvm object file dumper")
 guess-tool-llvm-ar = $(shell $(1) --help 2>&1 | grep -o "LLVM Archiver")

 # GNU Compiler Collection & GNU Binary Utilities
 guess-tool-gnu-gcc = $(shell $(1) -v 2>&1 | grep -o "gcc version")
 guess-tool-gnu-ld = $(shell $(1) -v 2>&1 | grep -o "GNU ld")
 guess-tool-gnu-objcopy = $(shell $(1) --version 2>&1 | grep -o "GNU objcopy")
 guess-tool-gnu-objdump = $(shell $(1) --version 2>&1 | grep -o "GNU objdump")
 guess-tool-gnu-ar = $(shell $(1) --version 2>&1 | grep -o "GNU ar")

 # Other tools
 guess-tool-dtc = $(shell $(1) --version 2>&1 | grep -o "Version: DTC")

 guess-tool = $(firstword $(foreach candidate,$(1), \
         $(if $(call guess-tool-$(candidate),$(2)),$(candidate))))

 #
 # Locate and identify tools belonging to each toolchain.
 #
 # Each tool class in each toolchain receives a variable of the form
 # `$(toolchain)-$(tool)` giving the associated path to the program. For example:
 #
 #   - `aarch64-ld` gives the linker for the AArch64 toolchain,
 #   - `aarch32-oc` gives the object copier for the AArch32 toolchain, and
 #   - `host-cc` gives the C compiler for the host toolchain.
 #
 # For each of these variables, if no program path is explicitly provided by the
 # parent Makefile then the C compiler is queried (if supported) for its
 # location. This is done via the `guess-$(tool)-$(tool-class)` set of functions.
 # For example:
 #
 #   - `guess-arm-clang-ld` guesses the linker via Arm Clang,
 #   - `guess-llvm-clang-as` guesses the assembler via LLVM Clang, and
 #   - `guess-gnu-gcc-od` guesses the object dumper via GNU GCC.
 #
 # If the C compiler cannot provide the location (or the tool class is the C
 # compiler), then it is assigned the value of the `$(toolchain)-$(tool)-default`
 # variable.
 #

 guess-arm-clang-cpp = $(1) # Use the C compiler
 guess-arm-clang-as = $(1) # Use the C compiler
 guess-arm-clang-ld = # Fall back to `$(toolchain)-ld-default`
 guess-arm-clang-oc = # Fall back to `$(toolchain)-oc-default`
 guess-arm-clang-od = # Fall back to `$(toolchain)-od-default`
 guess-arm-clang-ar = # Fall back to `$(toolchain)-ar-default`

 guess-llvm-clang-cpp = $(1) # Use the C compiler
 guess-llvm-clang-as = $(1) # Use the C compiler
 guess-llvm-clang-ld = $(shell $(1) --print-prog-name ld.lld 2>$(nul))
 guess-llvm-clang-oc = $(shell $(1) --print-prog-name llvm-objcopy 2>$(nul))
 guess-llvm-clang-od = $(shell $(1) --print-prog-name llvm-objdump 2>$(nul))
 guess-llvm-clang-ar = $(shell $(1) --print-prog-name llvm-ar 2>$(nul))

 guess-gnu-gcc-cpp = $(1) # Use the C compiler
 guess-gnu-gcc-as = $(1) # Use the C compiler
 guess-gnu-gcc-ld = $(1) # Use the C compiler
 guess-gnu-gcc-oc = $(shell $(1) --print-prog-name objcopy 2>$(nul))
 guess-gnu-gcc-od = $(shell $(1) --print-prog-name objdump 2>$(nul))
 guess-gnu-gcc-ar = $(patsubst %$(notdir $(1)),%$(subst gcc,gcc-ar,$(notdir $(1))),$(1))

 define locate-toolchain-tool-cc
         $(eval toolchain := $(1))

         $(toolchain)-cc := $$(strip \
                 $$(or $$($(toolchain)-cc),$$($(toolchain)-cc-default)))
         $(toolchain)-cc-id := $$(strip \
                 $$(call guess-tool,$$(tools-cc),$$($(toolchain)-cc)))
 endef

 define locate-toolchain-tool
         $(eval toolchain := $(1))
         $(eval tool-class := $(2))

         ifndef $(toolchain)-$(tool-class)
                 $(toolchain)-$(tool-class) := $$(strip \
                         $$(call guess-$$($(toolchain)-cc-id)-$(tool-class),$$($(toolchain)-cc)))

                 ifeq ($$($(toolchain)-$(tool-class)),)
                         $(toolchain)-$(tool-class) := $$(strip \
                                 $$($(toolchain)-$(tool-class)-default))
                 endif
         endif

         $(toolchain)-$(tool-class)-id := $$(strip \
                 $$(call guess-tool,$$(tools-$(tool-class)),$$($$(toolchain)-$(tool-class))))
 endef

 define canonicalize-toolchain-tool-path
         $(eval toolchain := $(1))
         $(eval tool-class := $(2))

         $(toolchain)-$(tool-class) := $$(strip $$(or \
                 $$(call which,$$($(toolchain)-$(tool-class))), \
                 $$($(toolchain)-$(tool-class))))
 endef

 define locate-toolchain
         $(eval toolchain := $(1))

         $$(eval $$(call locate-toolchain-tool-cc,$(toolchain)))
         $$(eval $$(call canonicalize-toolchain-tool-path,$(toolchain),cc))

         $$(foreach tool-class,$$(filter-out cc,$$(tool-classes)), \
                 $$(eval $$(call locate-toolchain-tool,$(toolchain),$$(tool-class))) \
                 $$(eval $$(call canonicalize-toolchain-tool-path,$(toolchain),$$(tool-class))))
 endef

 $(foreach toolchain,$(toolchains), \
         $(eval $(call locate-toolchain,$(toolchain))))
	#
	# Copyright (c) 2023-2024, Arm Limited and Contributors. All rights reserved.
	#
	# SPDX-License-Identifier: BSD-3-Clause
	#

	#
	# TF-A uses three toolchains:
	#
	# - The host toolchain (`host`) for building native tools
	# - The AArch32 toolchain (`aarch32`) for building Arm AArch32 images
	# - The AArch64 toolchain (`aarch64`) for building Arm AArch64 images
	#
	# In the main Makefile only one of the two Arm toolchains is enabled in any
	# given build, but individual tools and libraries may need access to both.
	#

	toolchains ?= host $(ARCH)

	ifneq ($(filter host,$(toolchains)),)
	host-cc := $(HOSTCC)
	host-cpp := $(HOSTCPP)

	host-as := $(HOSTAS)

	host-ld := $(HOSTLD)
	host-oc := $(HOSTOC)
	host-od := $(HOSTOD)
	host-ar := $(HOSTAR)

	host-dtc := $(HOSTDTC)
	endif

	ifneq ($(filter aarch32,$(toolchains)),)
	aarch32-cc := $(if $(filter-out default,$(origin CC)),$(CC))
	aarch32-cpp := $(if $(filter-out default,$(origin CPP)),$(CPP))

	aarch32-as := $(if $(filter-out default,$(origin AS)),$(AS))

	aarch32-ld := $(if $(filter-out default,$(origin LD)),$(LD))
	aarch32-oc := $(if $(filter-out default,$(origin OC)),$(OC))
	aarch32-od := $(if $(filter-out default,$(origin OD)),$(OD))
	aarch32-ar := $(if $(filter-out default,$(origin AR)),$(AR))

	aarch32-dtc := $(if $(filter-out default,$(origin DTC)),$(DTC))
	endif

	ifneq ($(filter aarch64,$(toolchains)),)
	aarch64-cc := $(if $(filter-out default,$(origin CC)),$(CC))
	aarch64-cpp := $(if $(filter-out default,$(origin CPP)),$(CPP))

	aarch64-as := $(if $(filter-out default,$(origin AS)),$(AS))

	aarch64-ld := $(if $(filter-out default,$(origin LD)),$(LD))
	aarch64-oc := $(if $(filter-out default,$(origin OC)),$(OC))
	aarch64-od := $(if $(filter-out default,$(origin OD)),$(OD))
	aarch64-ar := $(if $(filter-out default,$(origin AR)),$(AR))

	aarch64-dtc := $(if $(filter-out default,$(origin DTC)),$(DTC))
	endif

	include $(dir $(lastword $(MAKEFILE_LIST)))build_env.mk
	include $(addprefix $(dir $(lastword $(MAKEFILE_LIST)))toolchains/, \
	$(addsuffix .mk,$(toolchains)))

	#
	# Configure tool classes that we recognize.
	#
	# In the context of this build system, a tool class identifies a specific role
	# or type of tool in the toolchain.
	#

	# C-related tools
	tool-classes := cc # C compilers
	tool-classes += cpp # C preprocessors

	# Assembly-related tools
	tool-classes += as # Assemblers

	# Linking and object-handling tools
	tool-classes += ld # Linkers
	tool-classes += oc # Object copiers
	tool-classes += od # Object dumpers
	tool-classes += ar # Archivers

	# Other tools
	tool-classes += dtc # Device tree compilers

	#
	# Configure tools that we recognize.
	#
	# Here we declare the list of specific toolchain tools that we know how to
	# interact with. We don't organize these into tool classes yet - that happens
	# further down.
	#

	# Arm Compiler for Embedded
	tools := arm-clang # armclang
	tools += arm-link # armlink
	tools += arm-ar # armar
	tools += arm-fromelf # fromelf

	# LLVM Project
	tools += llvm-clang # clang
	tools += llvm-lld # lld
	tools += llvm-objcopy # llvm-objcopy
	tools += llvm-objdump # llvm-objdump
	tools += llvm-ar # llvm-ar

	# GNU Compiler Collection & GNU Binary Utilities
	tools += gnu-gcc # gcc
	tools += gnu-ld # ld
	tools += gnu-objcopy # objcopy
	tools += gnu-objdump # objdump
	tools += gnu-ar # gcc-ar

	# Other tools
	tools += dtc # Device Tree Compiler

	#
	# Assign tools to tool classes.
	#
	# Multifunctional tools, i.e. tools which can perform multiple roles in a
	# toolchain, may be specified in multiple tool class lists. For example, a C
	# compiler which can also perform the role of a linker may be placed in both
	# `tools-cc` and `tools-ld`.
	#

	# C-related tools
	tools-cc := arm-clang llvm-clang gnu-gcc # C compilers
	tools-cpp := arm-clang llvm-clang gnu-gcc # C preprocessors

	# Assembly-related tools
	tools-as := arm-clang llvm-clang gnu-gcc # Assemblers

	# Linking and object-handling tools
	tools-ld := arm-clang arm-link llvm-clang llvm-lld gnu-gcc gnu-ld # Linkers
	tools-oc := arm-fromelf llvm-objcopy gnu-objcopy # Object copiers
	tools-od := arm-fromelf llvm-objdump gnu-objdump # Object dumpers
	tools-ar := arm-ar llvm-ar gnu-ar # Archivers

	# Other tools
	tools-dtc := dtc # Device tree compilers

	define check-tool-class-tools
	$(eval tool-class := $(1))

	ifndef tools-$(tool-class)
	$$(error no tools registered to handle tool class `$(tool-class)`)
	endif
	endef

	$(foreach tool-class,$(tool-classes), \
	$(eval $(call check-tool-class-tools,$(tool-class))))

	#
	# Default tools for each toolchain.
	#
	# Toolchains can specify a default path to any given tool with a tool class.
	# These values are used in the absence of user-specified values, and are
	# configured by the makefile for each toolchain using variables of the form:
	#
	# - $(toolchain)-$(tool-class)-default
	#
	# For example, the default C compiler for the AArch32 and AArch64 toolchains
	# could be configured with:
	#
	# - aarch32-cc-default
	# - aarch64-cc-default
	#

	define check-toolchain-tool-class-default
	$(eval toolchain := $(1))
	$(eval tool-class := $(2))

	ifndef $(toolchain)-$(tool-class)-default
	$$(error no default value specified for tool class `$(tool-class)` of toolchain `$(toolchain)`)
	endif
	endef

	define check-toolchain-tool-class-defaults
	$(eval toolchain := $(1))

	$(foreach tool-class,$(tool-classes), \
	$(eval $(call check-toolchain-tool-class-default,$(toolchain),$(tool-class))))
	endef

	$(foreach toolchain,$(toolchains), \
	$(eval $(call check-toolchain-tool-class-defaults,$(toolchain))))

	#
	# Helper functions to identify toolchain tools.
	#
	# The functions defined in this section return a tool identifier when given a
	# path to a binary. We generally check a help or version string to more reliably
	# identify tools than by looking at the path alone (e.g. `gcc` on macOS is
	# actually Apple Clang).
	#
	# Each tool-guessing function (`guess-tool-$(tool)`) takes a single argument
	# giving the path to the tool to guess, and returns a non-empty value if the
	# tool corresponds to the tool identifier `$(tool)`:
	#
	# $(call guess-tool-llvm-clang,aarch64-none-elf-gcc) # <empty>
	# $(call guess-tool-gnu-gcc,aarch64-none-elf-gcc) # <non-empty>
	#
	# The `guess-tool` function tries to find the corresponding tool identifier
	# for a tool given its path. It takes two arguments:
	#
	# - $(1): a list of candidate tool identifiers to check
	# - $(2): the path to the tool to identify
	#
	# If any of the guess functions corresponding to candidate tool identifiers
	# return a non-empty value then the tool identifier of the first function to do
	# so is returned:
	#
	# $(call guess-tool,gnu-gcc llvm-clang,armclang) # <empty>
	# $(call guess-tool,gnu-gcc llvm-clang,clang-14) # llvm-clang
	# $(call guess-tool,gnu-gcc llvm-clang,aarch64-none-elf-gcc-12) # gnu-gcc
	#
	# Tools are checked in the order that they appear in `tools-$(tool-class)`, and
	# the first match is returned.
	#

	# Arm Compiler for Embedded
	guess-tool-arm-clang = $(shell $(1) --version 2>&1 \| grep -o "Tool: armclang")
	guess-tool-arm-link = $(shell $(1) --help 2>&1 \| grep -o "Tool: armlink")
	guess-tool-arm-fromelf = $(shell $(1) --help 2>&1 \| grep -o "Tool: fromelf")
	guess-tool-arm-ar = $(shell $(1) --version 2>&1 \| grep -o "Tool: armar")

	# LLVM Project
	guess-tool-llvm-clang = $(shell $(1) -v 2>&1 \| grep -o "clang version")
	guess-tool-llvm-lld = $(shell $(1) --help 2>&1 \| grep -o "OVERVIEW: lld")
	guess-tool-llvm-objcopy = $(shell $(1) --help 2>&1 \| grep -o "llvm-objcopy tool")
	guess-tool-llvm-objdump = $(shell $(1) --help 2>&1 \| grep -o "llvm object file dumper")
	guess-tool-llvm-ar = $(shell $(1) --help 2>&1 \| grep -o "LLVM Archiver")

	# GNU Compiler Collection & GNU Binary Utilities
	guess-tool-gnu-gcc = $(shell $(1) -v 2>&1 \| grep -o "gcc version")
	guess-tool-gnu-ld = $(shell $(1) -v 2>&1 \| grep -o "GNU ld")
	guess-tool-gnu-objcopy = $(shell $(1) --version 2>&1 \| grep -o "GNU objcopy")
	guess-tool-gnu-objdump = $(shell $(1) --version 2>&1 \| grep -o "GNU objdump")
	guess-tool-gnu-ar = $(shell $(1) --version 2>&1 \| grep -o "GNU ar")

	# Other tools
	guess-tool-dtc = $(shell $(1) --version 2>&1 \| grep -o "Version: DTC")

	guess-tool = $(firstword $(foreach candidate,$(1), \
	$(if $(call guess-tool-$(candidate),$(2)),$(candidate))))

	#
	# Locate and identify tools belonging to each toolchain.
	#
	# Each tool class in each toolchain receives a variable of the form
	# `$(toolchain)-$(tool)` giving the associated path to the program. For example:
	#
	# - `aarch64-ld` gives the linker for the AArch64 toolchain,
	# - `aarch32-oc` gives the object copier for the AArch32 toolchain, and
	# - `host-cc` gives the C compiler for the host toolchain.
	#
	# For each of these variables, if no program path is explicitly provided by the
	# parent Makefile then the C compiler is queried (if supported) for its
	# location. This is done via the `guess-$(tool)-$(tool-class)` set of functions.
	# For example:
	#
	# - `guess-arm-clang-ld` guesses the linker via Arm Clang,
	# - `guess-llvm-clang-as` guesses the assembler via LLVM Clang, and
	# - `guess-gnu-gcc-od` guesses the object dumper via GNU GCC.
	#
	# If the C compiler cannot provide the location (or the tool class is the C
	# compiler), then it is assigned the value of the `$(toolchain)-$(tool)-default`
	# variable.
	#

	guess-arm-clang-cpp = $(1) # Use the C compiler
	guess-arm-clang-as = $(1) # Use the C compiler
	guess-arm-clang-ld = # Fall back to `$(toolchain)-ld-default`
	guess-arm-clang-oc = # Fall back to `$(toolchain)-oc-default`
	guess-arm-clang-od = # Fall back to `$(toolchain)-od-default`
	guess-arm-clang-ar = # Fall back to `$(toolchain)-ar-default`

	guess-llvm-clang-cpp = $(1) # Use the C compiler
	guess-llvm-clang-as = $(1) # Use the C compiler
	guess-llvm-clang-ld = $(shell $(1) --print-prog-name ld.lld 2>$(nul))
	guess-llvm-clang-oc = $(shell $(1) --print-prog-name llvm-objcopy 2>$(nul))
	guess-llvm-clang-od = $(shell $(1) --print-prog-name llvm-objdump 2>$(nul))
	guess-llvm-clang-ar = $(shell $(1) --print-prog-name llvm-ar 2>$(nul))

	guess-gnu-gcc-cpp = $(1) # Use the C compiler
	guess-gnu-gcc-as = $(1) # Use the C compiler
	guess-gnu-gcc-ld = $(1) # Use the C compiler
	guess-gnu-gcc-oc = $(shell $(1) --print-prog-name objcopy 2>$(nul))
	guess-gnu-gcc-od = $(shell $(1) --print-prog-name objdump 2>$(nul))
	guess-gnu-gcc-ar = $(patsubst %$(notdir $(1)),%$(subst gcc,gcc-ar,$(notdir $(1))),$(1))

	define locate-toolchain-tool-cc
	$(eval toolchain := $(1))

	$(toolchain)-cc := $$(strip \
	$$(or $$($(toolchain)-cc),$$($(toolchain)-cc-default)))
	$(toolchain)-cc-id := $$(strip \
	$$(call guess-tool,$$(tools-cc),$$($(toolchain)-cc)))
	endef

	define locate-toolchain-tool
	$(eval toolchain := $(1))
	$(eval tool-class := $(2))

	ifndef $(toolchain)-$(tool-class)
	$(toolchain)-$(tool-class) := $$(strip \
	$$(call guess-$$($(toolchain)-cc-id)-$(tool-class),$$($(toolchain)-cc)))

	ifeq ($$($(toolchain)-$(tool-class)),)
	$(toolchain)-$(tool-class) := $$(strip \
	$$($(toolchain)-$(tool-class)-default))
	endif
	endif

	$(toolchain)-$(tool-class)-id := $$(strip \
	$$(call guess-tool,$$(tools-$(tool-class)),$$($$(toolchain)-$(tool-class))))
	endef

	define canonicalize-toolchain-tool-path
	$(eval toolchain := $(1))
	$(eval tool-class := $(2))

	$(toolchain)-$(tool-class) := $$(strip $$(or \
	$$(call which,$$($(toolchain)-$(tool-class))), \
	$$($(toolchain)-$(tool-class))))
	endef

	define locate-toolchain
	$(eval toolchain := $(1))

	$$(eval $$(call locate-toolchain-tool-cc,$(toolchain)))
	$$(eval $$(call canonicalize-toolchain-tool-path,$(toolchain),cc))

	$$(foreach tool-class,$$(filter-out cc,$$(tool-classes)), \
	$$(eval $$(call locate-toolchain-tool,$(toolchain),$$(tool-class))) \
	$$(eval $$(call canonicalize-toolchain-tool-path,$(toolchain),$$(tool-class))))
	endef

	$(foreach toolchain,$(toolchains), \
	$(eval $(call locate-toolchain,$(toolchain))))