100 lines
3.8 KiB
ReStructuredText
100 lines
3.8 KiB
ReStructuredText
|
===================
|
||
|
|
Availability Markup
|
||
|
|
===================
|
||
|
|
|
||
|
|
.. contents::
|
||
|
|
:local:
|
||
|
|
|
||
|
|
Overview
|
||
|
|
========
|
||
|
|
|
||
|
|
Libc++ is used as a system library on macOS and iOS (amongst others). In order
|
||
|
|
for users to be able to compile a binary that is intended to be deployed to an
|
||
|
|
older version of the platform, clang provides the
|
||
|
|
`availability attribute <https://clang.llvm.org/docs/AttributeReference.html#availability>`_
|
||
|
|
that can be placed on declarations to describe the lifecycle of a symbol in the
|
||
|
|
library.
|
||
|
|
|
||
|
|
Design
|
||
|
|
======
|
||
|
|
|
||
|
|
When a new feature is introduced that requires dylib support, a macro should be
|
||
|
|
created in include/__config to mark this feature as unavailable for all the
|
||
|
|
systems. For example::
|
||
|
|
|
||
|
|
// Define availability macros.
|
||
|
|
#if defined(_LIBCPP_USE_AVAILABILITY_APPLE)
|
||
|
|
# define _LIBCPP_AVAILABILITY_BAD_OPTIONAL_ACCESS __attribute__((unavailable))
|
||
|
|
#else if defined(_LIBCPP_USE_AVAILABILITY_SOME_OTHER_VENDOR)
|
||
|
|
# define _LIBCPP_AVAILABILITY_BAD_OPTIONAL_ACCESS __attribute__((unavailable))
|
||
|
|
#else
|
||
|
|
# define _LIBCPP_AVAILABILITY_BAD_OPTIONAL_ACCESS
|
||
|
|
#endif
|
||
|
|
|
||
|
|
When the library is updated by the platform vendor, the markup can be updated.
|
||
|
|
For example::
|
||
|
|
|
||
|
|
#define _LIBCPP_AVAILABILITY_SHARED_MUTEX \
|
||
|
|
__attribute__((availability(macosx,strict,introduced=10.12))) \
|
||
|
|
__attribute__((availability(ios,strict,introduced=10.0))) \
|
||
|
|
__attribute__((availability(tvos,strict,introduced=10.0))) \
|
||
|
|
__attribute__((availability(watchos,strict,introduced=3.0)))
|
||
|
|
|
||
|
|
In the source code, the macro can be added on a class if the full class requires
|
||
|
|
type info from the library for example::
|
||
|
|
|
||
|
|
_LIBCPP_BEGIN_NAMESPACE_EXPERIMENTAL
|
||
|
|
class _LIBCPP_EXCEPTION_ABI _LIBCPP_AVAILABILITY_BAD_OPTIONAL_ACCESS bad_optional_access
|
||
|
|
: public std::logic_error {
|
||
|
|
|
||
|
|
or on a particular symbol:
|
||
|
|
|
||
|
|
_LIBCPP_OVERRIDABLE_FUNC_VIS _LIBCPP_AVAILABILITY_SIZED_NEW_DELETE void operator delete(void* __p, std::size_t __sz) _NOEXCEPT;
|
||
|
|
|
||
|
|
|
||
|
|
Testing
|
||
|
|
=======
|
||
|
|
|
||
|
|
Some parameters can be passed to lit to run the test-suite and exercise the
|
||
|
|
availability.
|
||
|
|
|
||
|
|
* The `platform` parameter controls the deployment target. For example lit can
|
||
|
|
be invoked with `--param=platform=macosx10.8`. Default is the current host.
|
||
|
|
* The `use_system_cxx_lib` parameter indicates to use another library than the
|
||
|
|
just built one. Invoking lit with `--param=use_system_cxx_lib=true` will run
|
||
|
|
the test-suite against the host system library. Alternatively a path to the
|
||
|
|
directory containing a specific prebuilt libc++ can be used, for example:
|
||
|
|
`--param=use_system_cxx_lib=/path/to/macOS/10.8/`.
|
||
|
|
|
||
|
|
Tests can be marked as XFAIL based on multiple features made available by lit:
|
||
|
|
|
||
|
|
|
||
|
|
* if `--param=platform=macosx10.8` is passed, the following features will be available:
|
||
|
|
|
||
|
|
- availability
|
||
|
|
- availability=x86_64
|
||
|
|
- availability=macosx
|
||
|
|
- availability=x86_64-macosx
|
||
|
|
- availability=x86_64-apple-macosx10.8
|
||
|
|
- availability=macosx10.8
|
||
|
|
|
||
|
|
This feature is used to XFAIL a test that *is* using a class or a method marked
|
||
|
|
as unavailable *and* that is expected to *fail* if deployed on an older system.
|
||
|
|
|
||
|
|
* if `use_system_cxx_lib` and `--param=platform=macosx10.8` are passed to lit,
|
||
|
|
the following features will also be available:
|
||
|
|
|
||
|
|
- with_system_cxx_lib
|
||
|
|
- with_system_cxx_lib=x86_64
|
||
|
|
- with_system_cxx_lib=macosx
|
||
|
|
- with_system_cxx_lib=x86_64-macosx
|
||
|
|
- with_system_cxx_lib=x86_64-apple-macosx10.8
|
||
|
|
- with_system_cxx_lib=macosx10.8
|
||
|
|
|
||
|
|
This feature is used to XFAIL a test that is *not* using a class or a method
|
||
|
|
marked as unavailable *but* that is expected to fail if deployed on an older
|
||
|
|
system. For example, if the test exhibits a bug in the libc on a particular
|
||
|
|
system version, or if the test uses a symbol that is not available on an
|
||
|
|
older version of the dylib (but for which there is no availability markup,
|
||
|
|
otherwise the XFAIL should use `availability` above).
|