This avoids a ton of duplication and makes it easier to change a generic
target (for example, the "cortex-m" target) for all boards that use it.
Also, by making it possible to inherit properties from a parent target
specification, it is easier to support out-of-tree boards that don't
have to be updated so often. A target specification for a
special-purpose board can simply inherit the specification of a
supported chip and override the properites it needs to override (like
the programming interface).
Let the standard library think that it is compiling for js/wasm.
The most correct way of supporting bare metal Cortex-M targets would be
using the 'arm' build tag and specifying no OS or an 'undefined' OS
(perhaps GOOS=noos?). However, there is no build tag for specifying no
OS at all, the closest possible is GOOS=js which makes very few
assumptions.
Sadly GOOS=js also makes some assumptions: it assumes to be running with
GOARCH=wasm. This would not be such a problem, just add js, wasm and arm
as build tags. However, having two GOARCH build tags leads to an error
in internal/cpu: it defines variables for both architectures which then
conflict.
To work around these problems, the 'arm' target has been renamed to
'tinygo.arm', which should work around these problems. In the future, a
GOOS=noos (or similar) should be added which can work with any
architecture and doesn't implement OS-specific stuff.
Undefined symbols will be shown by the embedder, for example when
running generated wasm files in a browser.
In the future, this should probably become a fixed list again. But for
experimenting it's easier now to just ignore undefined symbols and
expect the JS to provide them.
A few changes to make sure compiler-rt is correctly compiled (and
doesn't include host headers, for example).
This improves support for AVR, but it still doesn't work. Compiler-rt
itself doesn't really work for AVR either.
This increases code size by 1 instruction (2 bytes) because LLVM isn't
yet smart enough to recognize that it doesn't need to clear a register
to use 0: it can just use r1 which is always 0 according to the
convention. It makes initialization a lot easier to read, however.
This allows the use of some compiler-generated builtins that are
hopefully compatible with LLVM. Example: println(uint8(foo))
Code size is unchanged normally but of course compiler builtins will
increase code size when actually used (for example with division).
This is kind of dirty with that huge list of linker params, but it works
and it produces smaller object files (probably because GCC is better
optimized for size).
