Errored: OpenSmalltalk/opensmalltalk-vm#1932 (Cog - 1cbb668)

CogVM source as per VMMaker.oscog-eem.2692

ThreadedFFIPlugins:
See https://github.com/OpenSmalltalk/opensmalltalk-vm/issues/443

FFI support for returning of a packed struct by value in X64 SysV

On X64/SysV struct up to 16 byte long can be passed by value into a pair of
8-byte registers. The problem is to know whether these are int (RAX RDX) or
float (XMM0 XMM1) registers or eventually a mix of...

For each 8-byte, we must know if it contains at least an int (in which case we
have to use an int register), or exclusively floating points (a pair of float
or a double). Previous algorithm did check first two fields, or last two
fields which does not correctly cover all cases...
For example int-int-float has last two fields int-float, though it will use
RAX XMM0.

So we have to know about struct layout... Unfortunately, this information is
not included into the compiledSpec. The idea here is to reconstruct the
information. See #registerTypeForStructSpecs:OfLength:

It's also impossible to cover the exotic alignments like packed structure
cases... But if we really want to pass that, this will mean passing the
alignment information, a more involved change of #compiledSpec (we need
up to 16 bits by field to handle that information since our FFI struct
are limited to 65535 bytes anyway).

For returning a struct, that's the same problem. We have four possible
combinations of int-float registers. Consequently, the idea is to analyze
the ffiRetSpec compiledSpec object thru CalloutState (it's the Smalltalk
WordArray object, not a pointer to its firstIndexableField) for performing
this analysis... Not sure if the best choice.

Since we have 4 different SixteenByte types, I have changed
value, since it's what will be used to memcpy to allocated ByteArray handle.

Checking the size of a struct is not the only condition for returning a struct
via registers. Some ABI like X64 SysV also mandates that struct fields be
properly aligned. Therefore, we cannot just rely on #returnStructInRegisters:.

Rename #returnStructInRegisters: -> #canReturnInRegistersStructOfSize:

Perform a more thorough analysis during the setup in #ffiCheckReturn:With:in:
The ABI will #encodeStructReturnTypeIn: a new callout state.
This structReturnType is telling how the struct should be returned
- via registers (and which registers)
- or via pointer to memory allocated by caller

This structReturnType will be used at time of:
- allocating the memory in caller - see #ffiCall:ArgArrayOrNil:NumArgs:
- dispatching to the correct FFI prototype - see ThreadedX64SysVFFIPlugin>>#ffiCalloutTo:SpecOnStack:in:
- copying back the struct contents to ExternalStructure handle (a ByteArray) - see #ffiReturnStruct:ofType:in:

Since structReturnType is encoded, it is not necessarily accessed directly,
but rather via new implementation of #returnStructInRegisters: whch now
takes the calloutState and knows how to decode its structReturnType.

Check for unaligned struct and pass them in MEMORY (alloca'd memory passed
thru a pointer).

Use a new (branchless) formulation for aligning the byteSize to next multiple
of fieldAlignment.

Encode registryType of invalid unaligned candidate as 2r110, and pass the
struct address returned by the foreign function in $RAX register in place
of callout limit when stuct is returned by MEMORY.

CoInterpreter: eliminate all but one compiler warning.

Cogit/Slang: fix several C compiler warnings re the Cogits.

Cogit: DUAL_MAPPED_CODE_ZONE (require -DDUAL_MAPPED_CODE_ZONE=1 to enable)

Fix denial of write/execute facility on modern Linuxes by dual mapping the code
zone in to a read/execute address range for code execution and a read/write
address range for code editing. Maintain codeToDataDelta and provide
codeXXXAt:put: to write at address + codeToDataDelta to the offset writable
address range.

Hence DUAL_MAPPED_CODE_ZONE requires a new executbale permissions applyer that
will also do the dual mapping, sqMakeMemoryExecutableFrom:To:CodeToDataDelta:.

Provide writableMethodFor: as a convenience for obtaining a writable cogMethod.

No longer have the fillInXXXHeaderYYY: methods answer anything since they're
given the writable header, not the actual header.

Cogit:
Refactor indexForSelector:in:at: to indexForSelector:in: in the back end so it
can be inlined (via a macro).

Slang:
emit constant for (M << N) and (M - N) - L for constant integers.
Fix in slang case statement expansion labels.

During expansion in case statements, trees are duplicated and expanded.