RE: [bootstrappable] ARM Unified Assembly Language - GNU as does some weird stuff

[Orians, Jeremiah (DTMB)]

> (1) b #60
> It seems that GNU as ignores the immediate entirely and just always encodes
> #0 (to test, do ".syntax unified" and then "b #60" in GNU as).  WTF?
> Likewise with bl, blx.

All assemblers (except M1) do that because the linker is to populate that value 
at link time using the symbol table to allow code segment relocation.

> (2) push #4
> It works in GNU as--but is it specified by ARM to push the register r2 ?
> I think exposing ISA implementation details like that is a leaky 
> abstraction--and no good can come from it.
> Likewise with pop, stm*, ldm*.

Well arm doesn't actually have a push/pop instructions, only load and store 
instructions

> GNU as fails to assemble these.
And no one cared enough to fix it for 30 years? Is it possible something is 
missed?

> (4) lsl r1, #4, #2
> GNU as encodes exactly the same as "lsl r1, #4"--drops the "#2" silently.
4 << 2 is 16. Log2(16) == 4; sounds about right

-Jeremiah