From 61d417ceff90c4bd99bfed082d81bcc33ecf5a45 Mon Sep 17 00:00:00 2001 From: Jonas Devlieghere Date: Thu, 7 Jul 2022 08:48:21 -0700 Subject: [PATCH] Revert "[libc++] Use ABI tags instead of internal linkage to provide per-TU insulation" This reverts commit 9ee97ce3b8305c5762ec34eecb4daf379984c95b. --- libcxx/CMakeLists.txt | 2 + libcxx/cmake/caches/Apple.cmake | 1 + libcxx/docs/BuildingLibcxx.rst | 9 ++++ libcxx/docs/DesignDocs/VisibilityMacros.rst | 51 ++++++++++++++++++++ libcxx/docs/ReleaseNotes.rst | 5 -- libcxx/include/__config | 56 ++++++++-------------- libcxx/include/__config_site.in | 1 + .../libcxx/strings/basic.string/PR42676.sh.cpp | 22 +++++++++ 8 files changed, 106 insertions(+), 41 deletions(-) create mode 100644 libcxx/test/libcxx/strings/basic.string/PR42676.sh.cpp diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt index 3d63bb0..b118007 100644 --- a/libcxx/CMakeLists.txt +++ b/libcxx/CMakeLists.txt @@ -205,6 +205,7 @@ if (NOT ("${LIBCXX_TYPEINFO_COMPARISON_IMPLEMENTATION}" IN_LIST TYPEINFO_COMPARI LIBCXX_TYPEINFO_COMPARISON_IMPLEMENTATION") endif() +option(LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT "Enable per TU ABI insulation by default. To be used by vendors." OFF) set(LIBCXX_ABI_DEFINES "" CACHE STRING "A semicolon separated list of ABI macros to define in the site config header.") option(LIBCXX_EXTRA_SITE_DEFINES "Extra defines to add into __config_site") option(LIBCXX_USE_COMPILER_RT "Use compiler-rt instead of libgcc" OFF) @@ -846,6 +847,7 @@ config_define(${LIBCXX_ABI_VERSION} _LIBCPP_ABI_VERSION) config_define(${LIBCXX_ABI_NAMESPACE} _LIBCPP_ABI_NAMESPACE) config_define_if(LIBCXX_ABI_FORCE_ITANIUM _LIBCPP_ABI_FORCE_ITANIUM) config_define_if(LIBCXX_ABI_FORCE_MICROSOFT _LIBCPP_ABI_FORCE_MICROSOFT) +config_define_if(LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT _LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT) config_define_if_not(LIBCXX_ENABLE_THREADS _LIBCPP_HAS_NO_THREADS) config_define_if_not(LIBCXX_ENABLE_MONOTONIC_CLOCK _LIBCPP_HAS_NO_MONOTONIC_CLOCK) if (NOT LIBCXX_TYPEINFO_COMPARISON_IMPLEMENTATION STREQUAL "default") diff --git a/libcxx/cmake/caches/Apple.cmake b/libcxx/cmake/caches/Apple.cmake index ea701a4..db567bd 100644 --- a/libcxx/cmake/caches/Apple.cmake +++ b/libcxx/cmake/caches/Apple.cmake @@ -8,6 +8,7 @@ set(LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY OFF CACHE BOOL "") set(LIBCXX_ENABLE_STATIC ON CACHE BOOL "") set(LIBCXX_ENABLE_SHARED ON CACHE BOOL "") set(LIBCXX_CXX_ABI libcxxabi CACHE STRING "") +set(LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT ON CACHE BOOL "") set(LIBCXX_ENABLE_BACKWARDS_COMPATIBILITY_DEBUG_MODE_SYMBOLS OFF CACHE BOOL "") set(LIBCXX_ENABLE_VENDOR_AVAILABILITY_ANNOTATIONS ON CACHE BOOL "") set(LIBCXX_ENABLE_INCOMPLETE_FEATURES OFF CACHE BOOL "") diff --git a/libcxx/docs/BuildingLibcxx.rst b/libcxx/docs/BuildingLibcxx.rst index 5069c7f..3f4e314 100644 --- a/libcxx/docs/BuildingLibcxx.rst +++ b/libcxx/docs/BuildingLibcxx.rst @@ -412,6 +412,15 @@ libc++ Feature Options Use the specified GCC toolchain and standard library when building the native stdlib benchmark tests. +.. option:: LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT:BOOL + + **Default**: ``OFF`` + + Pick the default for whether to constrain ABI-unstable symbols to + each individual translation unit. This setting controls whether + `_LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT` is defined by default -- + see the documentation of that macro for details. + libc++ ABI Feature Options -------------------------- diff --git a/libcxx/docs/DesignDocs/VisibilityMacros.rst b/libcxx/docs/DesignDocs/VisibilityMacros.rst index d1c1626..a165fc4 100644 --- a/libcxx/docs/DesignDocs/VisibilityMacros.rst +++ b/libcxx/docs/DesignDocs/VisibilityMacros.rst @@ -65,6 +65,41 @@ Visibility Macros ABI, we should create a new _LIBCPP_HIDE_FROM_ABI_AFTER_XXX macro, and we can use it to start removing symbols from the ABI after that stable version. +**_LIBCPP_HIDE_FROM_ABI_PER_TU** + This macro controls whether symbols hidden from the ABI with `_LIBCPP_HIDE_FROM_ABI` + are local to each translation unit in addition to being local to each final + linked image. This macro is defined to either 0 or 1. When it is defined to + 1, translation units compiled with different versions of libc++ can be linked + together, since all non ABI-facing functions are local to each translation unit. + This allows static archives built with different versions of libc++ to be linked + together. This also means that functions marked with `_LIBCPP_HIDE_FROM_ABI` + are not guaranteed to have the same address across translation unit boundaries. + + When the macro is defined to 0, there is no guarantee that translation units + compiled with different versions of libc++ can interoperate. However, this + leads to code size improvements, since non ABI-facing functions can be + deduplicated across translation unit boundaries. + + This macro can be defined by users to control the behavior they want from + libc++. The default value of this macro (0 or 1) is controlled by whether + `_LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT` is defined, which is intended to + be used by vendors only (see below). + +**_LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT** + This macro controls the default value for `_LIBCPP_HIDE_FROM_ABI_PER_TU`. + When the macro is defined, per TU ABI insulation is enabled by default, and + `_LIBCPP_HIDE_FROM_ABI_PER_TU` is defined to 1 unless overridden by users. + Otherwise, per TU ABI insulation is disabled by default, and + `_LIBCPP_HIDE_FROM_ABI_PER_TU` is defined to 0 unless overridden by users. + + This macro is intended for vendors to control whether they want to ship + libc++ with per TU ABI insulation enabled by default. Users can always + control the behavior they want by defining `_LIBCPP_HIDE_FROM_ABI_PER_TU` + appropriately. + + By default, this macro is not defined, which means that per TU ABI insulation + is not provided unless explicitly overridden by users. + **_LIBCPP_TYPE_VIS** Mark a type's typeinfo, vtable and members as having default visibility. This attribute cannot be used on class templates. @@ -159,6 +194,22 @@ Visibility Macros versioning namespace. This allows throwing and catching some exception types between libc++ and libstdc++. +**_LIBCPP_INTERNAL_LINKAGE** + Mark the affected entity as having internal linkage (i.e. the `static` + keyword in C). This is only a best effort: when the `internal_linkage` + attribute is not available, we fall back to forcing the function to be + inlined, which approximates internal linkage since an externally visible + symbol is never generated for that function. This is an internal macro + used as an implementation detail by other visibility macros. Never mark + a function or a class with this macro directly. + +**_LIBCPP_ALWAYS_INLINE** + Forces inlining of the function it is applied to. For visibility purposes, + this macro is used to make sure that an externally visible symbol is never + generated in an object file when the `internal_linkage` attribute is not + available. This is an internal macro used by other visibility macros, and + it should not be used directly. + Links ===== diff --git a/libcxx/docs/ReleaseNotes.rst b/libcxx/docs/ReleaseNotes.rst index c6eb835..c2917d4 100644 --- a/libcxx/docs/ReleaseNotes.rst +++ b/libcxx/docs/ReleaseNotes.rst @@ -224,8 +224,3 @@ Build System Changes means that the same set of installed headers works for both DLL and static linkage. This means that distributors finally can build both library versions with a single CMake invocation. - -- The ``LIBCXX_HIDE_FROM_ABI_PER_TU_BY_DEFAULT`` configuration option has been removed. Indeed, - the risk of ODR violations from mixing different versions of libc++ in the same program has - been mitigated with a different technique that is simpler and does not have the drawbacks of - using internal linkage. diff --git a/libcxx/include/__config b/libcxx/include/__config index 22c2ed7..e4b7d25 100644 --- a/libcxx/include/__config +++ b/libcxx/include/__config @@ -26,13 +26,6 @@ # define _LIBCPP_VERSION 15000 -# define _LIBCPP_CONCAT_IMPL(_X, _Y) _X##_Y -# define _LIBCPP_CONCAT(_X, _Y) _LIBCPP_CONCAT_IMPL(_X, _Y) - -// Valid C++ identifier that revs with every libc++ version. This can be used to -// generate identifiers that must be unique for every released libc++ version. -# define _LIBCPP_VERSIONED_IDENTIFIER _LIBCPP_CONCAT(v, _LIBCPP_VERSION) - # if __STDC_HOSTED__ == 0 # define _LIBCPP_FREESTANDING # endif @@ -575,6 +568,12 @@ typedef __char32_t char32_t; # endif // defined(_LIBCPP_OBJECT_FORMAT_COFF) +# if __has_attribute(internal_linkage) +# define _LIBCPP_INTERNAL_LINKAGE __attribute__((internal_linkage)) +# else +# define _LIBCPP_INTERNAL_LINKAGE _LIBCPP_ALWAYS_INLINE +# endif + # if __has_attribute(exclude_from_explicit_instantiation) # define _LIBCPP_EXCLUDE_FROM_EXPLICIT_INSTANTIATION __attribute__((__exclude_from_explicit_instantiation__)) # else @@ -584,35 +583,20 @@ typedef __char32_t char32_t; # define _LIBCPP_EXCLUDE_FROM_EXPLICIT_INSTANTIATION _LIBCPP_ALWAYS_INLINE # endif -// This macro marks a symbol as being hidden from libc++'s ABI. This is achieved -// on two levels: -// 1. The symbol is given hidden visibility, which ensures that users won't start exporting -// symbols from their dynamic library by means of using the libc++ headers. This ensures -// that those symbols stay private to the dynamic library in which it is defined. -// -// 2. The symbol is given an ABI tag that changes with each version of libc++. This ensures -// that no ODR violation can arise from mixing two TUs compiled with different versions -// of libc++ where we would have changed the definition of a symbol. If the symbols shared -// the same name, the ODR would require that their definitions be token-by-token equivalent, -// which basically prevents us from being able to make any change to any function in our -// headers. Using this ABI tag ensures that the symbol name is "bumped" artificially at -// each release, which lets us change the definition of these symbols at our leisure. -// Note that historically, this has been achieved in various ways, including force-inlining -// all functions or giving internal linkage to all functions. Both these (previous) solutions -// suffer from drawbacks that lead notably to code bloat. -// -// Note that we use _LIBCPP_EXCLUDE_FROM_EXPLICIT_INSTANTIATION to ensure that we don't depend -// on _LIBCPP_HIDE_FROM_ABI methods of classes explicitly instantiated in the dynamic library. -// -// TODO: We provide a escape hatch with _LIBCPP_NO_ABI_TAG for folks who want to avoid increasing -// the length of symbols with an ABI tag. In practice, we should remove the escape hatch and -// use compression mangling instead, see https://github.com/itanium-cxx-abi/cxx-abi/issues/70. -# ifndef _LIBCPP_NO_ABI_TAG -# define _LIBCPP_HIDE_FROM_ABI \ - _LIBCPP_HIDDEN _LIBCPP_EXCLUDE_FROM_EXPLICIT_INSTANTIATION \ - __attribute__((__abi_tag__(_LIBCPP_TOSTRING(_LIBCPP_VERSIONED_IDENTIFIER)))) -# else -# define _LIBCPP_HIDE_FROM_ABI _LIBCPP_HIDDEN _LIBCPP_EXCLUDE_FROM_EXPLICIT_INSTANTIATION +# ifndef _LIBCPP_HIDE_FROM_ABI_PER_TU +# ifndef _LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT +# define _LIBCPP_HIDE_FROM_ABI_PER_TU 0 +# else +# define _LIBCPP_HIDE_FROM_ABI_PER_TU 1 +# endif +# endif + +# ifndef _LIBCPP_HIDE_FROM_ABI +# if _LIBCPP_HIDE_FROM_ABI_PER_TU +# define _LIBCPP_HIDE_FROM_ABI _LIBCPP_HIDDEN _LIBCPP_INTERNAL_LINKAGE +# else +# define _LIBCPP_HIDE_FROM_ABI _LIBCPP_HIDDEN _LIBCPP_EXCLUDE_FROM_EXPLICIT_INSTANTIATION +# endif # endif # ifdef _LIBCPP_BUILDING_LIBRARY diff --git a/libcxx/include/__config_site.in b/libcxx/include/__config_site.in index 97892e9..c615575 100644 --- a/libcxx/include/__config_site.in +++ b/libcxx/include/__config_site.in @@ -13,6 +13,7 @@ #cmakedefine _LIBCPP_ABI_NAMESPACE @_LIBCPP_ABI_NAMESPACE@ #cmakedefine _LIBCPP_ABI_FORCE_ITANIUM #cmakedefine _LIBCPP_ABI_FORCE_MICROSOFT +#cmakedefine _LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT #cmakedefine _LIBCPP_HAS_NO_THREADS #cmakedefine _LIBCPP_HAS_NO_MONOTONIC_CLOCK #cmakedefine _LIBCPP_HAS_MUSL_LIBC diff --git a/libcxx/test/libcxx/strings/basic.string/PR42676.sh.cpp b/libcxx/test/libcxx/strings/basic.string/PR42676.sh.cpp new file mode 100644 index 0000000..2170915 --- /dev/null +++ b/libcxx/test/libcxx/strings/basic.string/PR42676.sh.cpp @@ -0,0 +1,22 @@ +//===----------------------------------------------------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// + +// Regression test for PR42676. + +// RUN: %{cxx} %{flags} %s -o %t.exe %{compile_flags} %{link_flags} -D_LIBCPP_HIDE_FROM_ABI_PER_TU +// RUN: %{run} + +#include +#include + +int main(int, char**) { + std::string s1(10u, '-', std::allocator()); (void)s1; + std::string s2("hello", std::allocator()); (void)s2; + std::string s3("hello"); (void)s3; + return 0; +} -- 2.7.4