This library uses GenericMetadataBuilder with a ReaderWriter that can read data and resolve pointers from MachO files, and emit a JSON representation of a dylib containing the built metadata.
We use LLVM's binary file readers to parse the MachO files and resolve fixups so we can follow pointers. This code is somewhat MachO specific, but could be generalized to other formats that LLVM supports.
rdar://116592577
When detecting that an associated type's substituted type is an opaque type, read out its opaque type descriptor to collect the names of protocols it must conform to.
When SWIFT_COMPACT_ABSOLUTE_FUNCTION_POINTER is enabled, relative direct
pointers whose pointees are functions will be turned into absolute
pointer at compile-time.
We have RelativeDirectPointer and RelativeIndirectablePointer. The latter
cannot be used with function pointers because it assumes the payload is
2-byte aligned and uses the least significant bit to dynamically
distinguish a direct pointer from an indirect pointer.
For resilient conformances, we want to use protocol dispatch thunks as
keys in the witness table template. They're not 2 byte aligned, and
they're always defined in a different image, so we need an unconditional
indirect relative pointer template.
This new format more efficiently represents existing information, while
more accurately encoding important information about nested generic
contexts with same-type and layout constraints that need to be evaluated
at runtime. It's also designed with an eye to forward- and
backward-compatible expansion for ABI stability with future Swift
versions.
Use the spare bits within the type reference field to describe the kinds
of type metadata records, so that we no longer need to rely on a
separate "flags" field.
There were places were RelativeDirectPointers were copied using bitwise copies, which is semantically wrong. This patch makes sure it cannot happen anymore.
initialization in-place on demand. Initialize parent metadata
references correctly on struct and enum metadata.
Also includes several minor improvements related to relative
pointers that I was using before deciding to simply switch the
parent reference to an absolute reference to get better access
patterns.
Includes a fix since the earlier commit to make enum metadata
writable if they have an unfilled payload size. This didn't show
up on Darwin because "constant" is currently unenforced there in
global data containing relocations.
This patch requires an associated LLDB change which is being
submitted in parallel.
initialization in-place on demand. Initialize parent metadata
references correctly on struct and enum metadata.
Also includes several minor improvements related to relative
pointers that I was using before deciding to simply switch the
parent reference to an absolute reference to get better access
patterns.
- Added missing ifdef guard in PointerIntEnum header
- Consistent naming convention for ifdef guards
- Consistent 'end namespace swift'
- Consistent single EOL at end of header files
This is the first patch in a series that will allow new protocol
requirements to be added resiliently, with the runtime filling in
default implementations in witness tables.
First, this adds a new flag to the protocol descriptor indicating
that the protocol is resilient. In this case, there are two
additional fields, MinimumWitnessTableSizeInWords and
DefaultWitnessTableSizeInWords, followed by tail-allocated
default witnesses.
The swift_getGenericWitnessTable() entry point now fills in the
default witnesses from the protocol if the given witness table
template is smaller than the expected witness table size.
This also changes the layout of instantiated witness tables to move
the address point to the end of private data. Previously the private
data came after the requirements, but this meant that adding new
requirements would require sliding the private data at runtime and
accessing it indirectly. It is much simpler to access it from
negative offsets instead.
I updated IRGen to emit the new metadata, but currently all protocols
are flagged as not resilient, and default witnesses are not emitted;
this will come in a subsequent patch once some more plumbing is
in place.
To avoid generating GOT entries for references to protocols defined
in the current module, I had to add some hacks to the existing hack
for this. I'll hopefully clean this up in a principled manner later.
We really want to apply offsets using wrapping (unsigned) arithmetic, albeit with sign extension. This is significant on 32-bit platforms, where "far" addresses could be more than 2GB apart, but still relative-referenced using 32-bit signed values, and offset addition could end up wrapping around. Factor the logic to add an offset to a pointer out into a function that performs the sacred casting dance to appease the UB gods.
We usually want to use 32-bit offsets, since we use them to reference other objects within the same small-code-model image. However, for data structures that are both compiler-generated and runtime-allocated, we may want to save the relocation in compile time, but need a full-width offset to be able to relatively reference things from the heap. NFC yet.
Decrease the size of nominal type descriptors and make them true-const by relative-addressing the other metadata they need to reference, which should all be included in the same image as the descriptor itself. Relative-referencing string constants exposes a bug in the Apple linker, which crashes when resolving relative relocations to coalesceable symbols (rdar://problem/22674524); work around this for now by revoking the `unnamed_addr`-ness of string constants that we take relative references to. (I haven't tested whether GNU ld or gold also have this problem on Linux; it may be possible to conditionalize the workaround to only apply to Darwin targets for now.)
of associated types in protocol witness tables.
We use the global access functions when the result isn't
dependent, and a simple accessor when the result can be cheaply
recovered from the conforming metadata. Otherwise, we add a
cache slot to a private section of the witness table, forcing
an instantiation per conformance. Like generic type metadata,
concrete instantiations of generic conformances are memoized.
There's a fair amount of code in this patch that can't be
dynamically tested at the moment because of the widespread
reliance on recursive expansion of archetypes / dependent
types. That's something we're now theoretically in a position
to change, and as we do so, we'll test more of this code.
This speculatively re-applies 7576a91009,
i.e. reverts commit 11ab3d537f.
We have not been able to duplicate the build failure in
independent testing; it might have been spurious or unrelated.
of associated types in protocol witness tables.
We use the global access functions when the result isn't
dependent, and a simple accessor when the result can be cheaply
recovered from the conforming metadata. Otherwise, we add a
cache slot to a private section of the witness table, forcing
an instantiation per conformance. Like generic type metadata,
concrete instantiations of generic conformances are memoized.
There's a fair amount of code in this patch that can't be
dynamically tested at the moment because of the widespread
reliance on recursive expansion of archetypes / dependent
types. That's something we're now theoretically in a position
to change, and as we do so, we'll test more of this code.
This reverts commit 6528ec2887, i.e.
it reapplies b1e3120a28, with a fix
to unbreak release builds.
This reverts commit b1e3120a28.
Reverting because this patch uses WitnessTableBuilder::PI in NDEBUG code.
That field only exists when NDEBUG is not defined, but now NextCacheIndex, a
field that exists regardless, is being updated based on information from PI.
This problem means that Release builds do not work.
of associated types in protocol witness tables.
We use the global access functions when the result isn't
dependent, and a simple accessor when the result can be cheaply
recovered from the conforming metadata. Otherwise, we add a
cache slot to a private section of the witness table, forcing
an instantiation per conformance. Like generic type metadata,
concrete instantiations of generic conformances are memoized.
There's a fair amount of code in this patch that can't be
dynamically tested at the moment because of the widespread
reliance on recursive expansion of archetypes / dependent
types. That's something we're now theoretically in a position
to change, and as we do so, we'll test more of this code.
Decrease the size of nominal type descriptors and make them true-const by relative-addressing the other metadata they need to reference, which should all be included in the same image as the descriptor itself. Relative-referencing string constants exposes a bug in the Apple linker, which crashes when resolving relative relocations to coalesceable symbols (rdar://problem/22674524); work around this for now by revoking the `unnamed_addr`-ness of string constants that we take relative references to. (I haven't tested whether GNU ld or gold also have this problem on Linux; it may be possible to conditionalize the workaround to only apply to Darwin targets for now.)
Not every relative address makes sense to be conditionally indirect, so separate RelativeIndirectablePointer (which takes a tag bit to indicate whether the reference is directly to the object in question or to memory containing its address, such as its GOT entry) and RelativeDirectPointer. NFC.
Swift SVN r31839
By using relative references, either directly to symbols internal to the current TU, or to the GOT entry for external symbols, we avoid unnecessary runtime relocations, and we save space on 64-bit platforms, since a single image is still <2GB in size. For the 64-bit standard library, this trades 26KB of fake-const data in __DATA,__swift1_proto for 13KB of true-const data in __TEXT,__swift2_proto. Implements rdar://problem/22334380.
Swift SVN r31555
