build: refactor toolchain detection
This change refactors how we identify the toolchain, with the ultimate
aim of eventually cleaning up the various mechanisms that we employ to
configure default tools, identify the tools in use, and configure
toolchain flags.
To do this, we introduce three new concepts in this change:
- Toolchain identifiers,
- Tool class identifiers, and
- Tool identifiers.
Toolchain identifiers identify a configurable chain of tools targeting
one platform/machine/architecture. Today, these are:
- The host machine, which receives the `host` identifier,
- The AArch32 architecture, which receives the `aarch32` identifier, and
- The AArch64 architecture, which receivs the `aarch64` identifier.
The tools in a toolchain may come from different vendors, and are not
necessarily expected to come from one single toolchain distribution. In
most cases it is perfectly valid to mix tools from different toolchain
distributions, with some exceptions (notably, link-time optimization
generally requires the compiler and the linker to be aligned).
Tool class identifiers identify a class (or "role") of a tool. C
compilers, assemblers and linkers are all examples of tool classes.
Tool identifiers identify a specific tool recognized and supported by
the build system. Every tool that can make up a part of a toolchain must
receive a tool identifier.
These new identifiers can be used to retrieve information about the
toolchain in a more standardized fashion.
For example, logic in a Makefile that should only execute when the C
compiler is GNU GCC can now check the tool identifier for the C compiler
in the relevant toolchain:
ifeq ($($(ARCH)-cc-id),gnu-gcc)
...
endif
Change-Id: Icc23e43aaa32f4fd01d8187c5202f5012a634e7c
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/make_helpers/unix.mk b/make_helpers/unix.mk
index 545ddfd..d285799 100644
--- a/make_helpers/unix.mk
+++ b/make_helpers/unix.mk
@@ -57,4 +57,7 @@
-${Q}rm -rf "${1}"
endef
+ nul := /dev/null
+
+ which = $(shell which $(1) 2>$(nul))
endif