[libcxx] By default, do not use internal_linkage to hide symbols from the ABI
Summary:
https://reviews.llvm.org/D49240 led to symbol size problems in Chromium, and
we expect this may be the case in other projects built in debug mode too.
Instead, unless users explicitly ask for internal_linkage, we use always_inline
like we used to.
In the future, when we have a solution that allows us to drop always_inline
without falling back on internal_linkage, we can replace always_inline by
that.
Note that this commit introduces a change in contract for existing libc++
users: by default, libc++ used to guarantee that TUs built with different
versions of libc++ could be linked together. With the introduction of the
_LIBCPP_HIDE_FROM_ABI_PER_TU macro, the default behavior is that TUs built
with different libc++ versions are not guaranteed to link. This is a change
in contract but not a change in behavior, since the current implementation
still allows linking TUs built with different libc++ versions together.
Reviewers: EricWF, mclow.lists, dexonsmith, hans, rnk
Subscribers: christof, cfe-commits
Differential Revision: https://reviews.llvm.org/D50652
llvm-svn: 339874
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 61cd68700927f4811e0803a135104e9c96b0d679
diff --git a/docs/BuildingLibcxx.rst b/docs/BuildingLibcxx.rst
index d0b03c6..daf9229 100644
--- a/docs/BuildingLibcxx.rst
+++ b/docs/BuildingLibcxx.rst
@@ -332,6 +332,15 @@
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
--------------------------