os: add Args stub

[cornelk]

Tnis allows code that relies on it to compile, the flags package compiles now. No real parameters are passed but Args[0] contains a static mock string.

Setting Args as recommended #541 (comment) did not work tho:

tinygo/src/runtime/runtime_unix.go

func main() int {
	args = []string{"/proc/self/exe2"}
	preinit()
	run()

has no effect, os.Args will still hold the old value

[aykevl]

Thank you, this is a welcome improvement to get more packages to compile (even if they aren't fully supported yet).

[aykevl]

I've looked a bit into why you can't initialize the arguments in runtime.main and there are two reasons:

1. You can't do heap allocations before the initHeap call. This can be worked around by calling malloc directly.
2. The interp package gets in the way. It assumes that all global variables are initialized with a package initializer (globals, init functions). Therefore, setting argumens in the main function at runtime will be ignored by package initializers, which often run at compile time (mainly for code size). This is tricky to solve, I'm not sure whether it can be solved without compiler changes.

[sevki]

@aykevl i saw this got merged, but it seems to break the dev branch with -gc=none is there another issue tracking the progress of this or work that needs to be done... I'm waiting to start a new job in a month so I have plenty of free time on my hands 😉

[aykevl]

i saw this got merged, but it seems to break the dev branch with -gc=none

Are you sure this is what broke -gc=none? -gc=none is already broken in the master branch (and I believe it has been broken for a while now):

tinygo flash -target=pca10040 -gc=none examples/blinky1
Global is external, but doesn't have external or weak linkage!
i8* ()* @runtime.alloc
error: verification failure after LLVM optimization passes

[aykevl]

Here is a PR to fix the -gc=none bug: #1236