commit 1854bb00c60367606f88600df4d601f0ec8e1c0a
author Daco Harkes <dacoharkes@google.com> Fri Jan 20 10:30:41 2023 +0000
committer Daco Harkes <dacoharkes@google.com> Fri Jan 20 10:30:41 2023 +0000
tree 4cb4008ae606a5f59dd95b36bf9f913c27d964fb
parent a43badab9f70e3837b58b62680afa95c2416c3f9

[vm/ffi] Support varargs in the backend

On ARM64 macos and ios, when varargs are used, the first vararg blocks
all cpu and fpu registers.

On Windows x64, when varargs are used, floating point arguments are
passed _both_ in the integer and double register.

The Windows logic requires a new kind of native location:
`BothNativeLocations`, which signals that a value needs to be copied
to both locations before an FFI call, and can be copied from any of
the two locations when getting an FFI callback.
TEST=runtime/vm/compiler/ffi/unit_tests/variadic_double/x64_win.expect

Note that integer arguments already block out the corresponding xmm
registers on Windows x64.

On System-V, an upper bound of the number of XMM registers used must
be passed in AL. (Not reflected in the unit tests here, but will be in
the dependent CL.)

On ARM (32 bit), using varargs forces the calling convention to be in
softfp mode even on hardfp supported devices.

On RISC-V, the FPU registers are blocked when using varargs.

TEST=runtime/vm/compiler/ffi/native_calling_convention_test.cc
Test outputs in: runtime/vm/compiler/ffi/unit_tests/variadic_*
Run test with `tools/test.py ffi_unit`.

Bug: https://github.com/dart-lang/sdk/issues/38578
Change-Id: Ic568f8156c1c28ac3d6a2144805edf8caaa0169c
Cq-Include-Trybots: luci.dart.try:vm-precomp-ffi-qemu-linux-release-arm-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/278342
Reviewed-by: Ryan Macnak <rmacnak@google.com>