Instead of always starting a new goroutine for the main goroutine, run
the main goroutine on the system stack.
The system stack is not occupied with scheduling, instead each goroutine
that wants to pause itself calls into the scheduler which will switch to
the next task (goroutine) to run, or sleeps.
There are various advantages of this over the previous system:
* When the program doesn't start a goroutine, the code size and RAM
consumption is close to what you'd get with `-scheduler=none`.
* When the program does start a goroutine, there is still a reduction
in RAM consumption because only one extra stack is needed.
* Because tasks directly switch to the next task to run, only a single
task switch is needed instead of two (goroutine -> scheduler ->
goroutine). This should improve task switching performance.
I kept the current behavior for WebAssembly/Asyncify. I looked into how
the same benefits can be realized for WebAssembly but couldn't easily
find how to do that. Maybe this can be done separately, or maybe we'll
just wait for the stack switching proposal to finish.
The code for Cortex-M is currently more complicated than I'd like, and
therefore can sometimes result in a slight increase in code size. I'd
like to fix this eventually but am still looking into good ways to do
this. I still think this change is generally beneficial because many
programs see big reductions in code size when compiling for Cortex-M.
This commit adds support for timer interrupts, replacing the busy loop
that was used before. It is perhaps the most simple interrupt to
implement and should serve as the basis for further interrupt support in
RISC-V.
Now that we use LLVM 9, RISC-V support in LLVM has far fewer bugs and we
can avoid the GNU toolchain.
* replace GNU linker with lld
* replace GCC with clang
Additionally, RISC-V was promoted to stable so it can be enabled by
default in CI.
The .sdata and .sbss sections are created by the compiler, but were not
present in the linker script. That means that the linker put them after
all other data/bss section, which happens to be where the heap also
resides.
This commit adds the .sdata and .sbss sections to the linker script,
which gets the blinky examples to work again on RISC-V.
This prevents it from being of type PROGBITS in lld 9, it should always
be NOBITS. It should fix the following error in lld 9:
ROM segments are non-contiguous
Ayke van Laethem
Yannis Huber