This is an implementation of the Windows ABI. It supports most features
(struct passing/returning, varargs, env). TLS is not yet supported.
This patch does not actually port QBE to Windows, it only allows QBE to
generate correct asm to target Windows. As a result, testing is
accomplished on a Linux host, by using a cross-compiling toolchain, and
running the resulting binaries by using wine. See:
TARGET=amd64_win tools/test.sh all
A few cross-platform tests were changed from 'long' to 'long long' in
driver code because long in C does not match the size of a QBE 'l' on
Windows.
It is mostly complete, but still has a few ABI bugs when passing
floats in structs, or when structs are passed partly in register,
and partly on stack.
amd64 lacks an instruction for this so it has to be implemented with
signed -> float casts:
- Word casting is done by zero-extending the word to a long and then doing
a regular signed cast.
- Long casting is done by dividing by two with correct rounding if the
highest bit is set and casting that to float, then adding
1 to mantissa with integer addition
Some abis, like the riscv one, treat
arguments differently depending on
whether they are variadic or not.
To prepare for the upcomming riscv
target, we change the variadic call
syntax and give meaning to the
location of the '...' marker.
# new syntax
%ret =w call $f(w %regular, ..., w %variadic)
By nature of their abis, the change
is backwards compatible for existing
targets.
I thought it would be harder (and maybe it is).
My fear was that a call must be always followed by
a parallel move from machine registers (this is an
assumption in both spill and rega). This however
remains true, because the ABI code generates a
dummy "copy RAX" by accident!