vasilito
cb424d7448
verify-patch-sanity.py validates every active recipe .patch has internally- consistent hunk line counts — catching the 'malformed patch at line N' failure at commit/CI/preflight time instead of hours into a cook. This cycle hit that class three times (qtwaylandscanner, sddm, xwayland), each only discovered when cookbook tried to apply the patch. Running it across the repo found 29 latent malformed patches (validated against GNU patch: e.g. relibc/P3-sysv-ipc reproduces 'malformed patch at line 22'). They were harmless only because they sit in vendored recipes (baked, not re- applied) — but would fail on any version-bump re-derivation. --fix recounts the hunk headers (body untouched) and repaired all 29. Wired into build-preflight.sh (Phase 1.0D) and redbear-ci.yml, with a unit test (test-patch-sanity.sh). Skips archived/legacy trees and unvalidatable formats (empty placeholders, bare-@@ git hunks).
102 lines
4.9 KiB
ReStructuredText
102 lines
4.9 KiB
ReStructuredText
========================
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Symbol Visibility Macros
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========================
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.. contents::
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:local:
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.. _visibility-macros:
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Overview
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========
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Libc++ uses various "visibility" macros in order to provide a stable ABI in
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both the library and the headers. These macros work by changing the
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visibility and inlining characteristics of the symbols they are applied to.
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The std namespace also has visibility attributes applied to avoid having to
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add visibility macros in as many places. Namespace std has default
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type_visibility to export RTTI and other type-specific information. Note that
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type_visibility is only supported by Clang, so this doesn't replace
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type-specific attributes. The only exception are enums, which GCC always gives
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default visibility, thus removing the need for any annotations.
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Visibility Macros
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=================
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**_LIBCPP_HIDDEN**
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Mark a symbol as hidden so it will not be exported from shared libraries.
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**_LIBCPP_EXPORTED_FROM_ABI**
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Mark a symbol as being part of our ABI. This includes functions that are part
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of the libc++ library, type information and other symbols. On Windows,
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this macro applies `dllimport`/`dllexport` to the symbol, and on other
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platforms it gives the symbol default visibility.
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**_LIBCPP_OVERRIDABLE_FUNC_VIS**
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Mark a symbol as being exported by the libc++ library, but allow it to be
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overridden locally. On non-Windows, this is equivalent to `_LIBCPP_FUNC_VIS`.
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This macro is applied to all `operator new` and `operator delete` overloads.
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**Windows Behavior**: Any symbol marked `dllimport` cannot be overridden
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locally, since `dllimport` indicates the symbol should be bound to a separate
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DLL. All `operator new` and `operator delete` overloads are required to be
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locally overridable, and therefore must not be marked `dllimport`. On Windows,
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this macro therefore expands to `__declspec(dllexport)` when building the
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library and has an empty definition otherwise.
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**_LIBCPP_HIDE_FROM_ABI**
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Mark a function as not being part of the ABI of any final linked image that
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uses it.
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**_LIBCPP_HIDE_FROM_ABI_AFTER_V1**
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Mark a function as being hidden from the ABI (per `_LIBCPP_HIDE_FROM_ABI`)
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when libc++ is built with an ABI version after ABI v1. This macro is used to
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maintain ABI compatibility for symbols that have been historically exported
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by libc++ in v1 of the ABI, but that we don't want to export in the future.
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This macro works as follows. When we build libc++, we either hide the symbol
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from the ABI (if the symbol is not part of the ABI in the version we're
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building), or we leave it included. From user code (i.e. when we're not
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building libc++), the macro always marks symbols as internal so that programs
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built using new libc++ headers stop relying on symbols that are removed from
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the ABI in a future version. Each time we release a new stable version of the
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ABI, we should create a new _LIBCPP_HIDE_FROM_ABI_AFTER_XXX macro, and we can
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use it to start removing symbols from the ABI after that stable version.
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**_LIBCPP_EXTERN_TEMPLATE_TYPE_VIS**
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Mark the member functions, typeinfo, and vtable of the type named in
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an extern template declaration as being exported by the libc++ library.
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This attribute must be specified on all extern class template declarations.
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This macro is used to export the member functions produced by the explicit
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instantiation in the dylib.
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**Windows Behavior**: `extern template` and `dllexport` are fundamentally
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incompatible *on a class template* on Windows; the former suppresses
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instantiation, while the latter forces it. Specifying both on the same
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declaration makes the class template be instantiated, which is not desirable
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inside headers. This macro therefore expands to `dllimport` outside of libc++
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but nothing inside of it (rather than expanding to `dllexport`); instead, the
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explicit instantiations themselves are marked as exported. Note that this
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applies *only* to extern *class* templates. Extern *function* templates obey
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regular import/export semantics, and applying `dllexport` directly to the
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extern template declaration (i.e. using `_LIBCPP_FUNC_VIS`) is the correct
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thing to do for them.
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**_LIBCPP_CLASS_TEMPLATE_INSTANTIATION_VIS**
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Mark the member functions, typeinfo, and vtable of an explicit instantiation
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of a class template as being exported by the libc++ library. This attribute
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must be specified on all class template explicit instantiations.
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It is only necessary to mark the explicit instantiation itself (as opposed to
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the extern template declaration) as exported on Windows, as discussed above.
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On all other platforms, this macro has an empty definition.
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Links
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=====
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* `[cfe-dev] Visibility in libc++ - 1 <http://lists.llvm.org/pipermail/cfe-dev/2013-July/030610.html>`_
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* `[cfe-dev] Visibility in libc++ - 2 <http://lists.llvm.org/pipermail/cfe-dev/2013-August/031195.html>`_
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* `[libcxx] Visibility fixes for Windows <http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20130805/085461.html>`_
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