Commit Graph

8 Commits

Author SHA1 Message Date
Louis Dionne a9c9183ca4 [libc++] Use the using_if_exists attribute when provided
As discussed on cfe-dev [1], use the using_if_exists Clang attribute when
the compiler supports it. This makes it easier to port libc++ on top of
new platforms that don't fully support the C Standard library.

Previously, libc++ would fail to build when trying to import a missing
declaration in a <cXXXX> header. With the attribute, the declaration will
simply not be imported into namespace std, and hence it won't be available
for libc++ to use. In many cases, the declarations were *not* actually
required for libc++ to work (they were only surfaced for users to use
them as std::XXXX), so not importing them into namespace std is acceptable.

The same thing could be achieved by conscious usage of `#ifdef` along
with platform detection, however that quickly creates a maintenance
problem as libc++ is ported to new platforms. Furthermore, this problem
is exacerbated when mixed with vendor internal-only platforms, which can
lead to difficulties maintaining a downstream fork of the library.

For the time being, we only use the using_if_exists attribute when it
is supported. At some point in the future, we will start removing #ifdef
paths that are unnecessary when the attribute is supported, and folks
who need those #ifdef paths will be required to use a compiler that
supports the attribute.

[1]: http://lists.llvm.org/pipermail/cfe-dev/2020-June/066038.html

Differential Revision: https://reviews.llvm.org/D90257
2021-06-04 09:55:21 -04:00
Louis Dionne 4cd6ca102a [libc++] NFC: Normalize `#endif //` comment indentation 2021-04-20 12:03:32 -04:00
Chandler Carruth 57b08b0944 Update more file headers across all of the LLVM projects in the monorepo
to reflect the new license. These used slightly different spellings that
defeated my regular expressions.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351648
2019-01-19 10:56:40 +00:00
Ed Schouten e0cf3b9a3c Make support for thread-unsafe C functions optional.
One of the aspects of CloudABI is that it aims to help you write code
that is thread-safe out of the box. This is very important if you want
to write libraries that are easy to reuse. For CloudABI we decided to
not provide the thread-unsafe functions. So far this is working out
pretty well, as thread-unsafety issues are detected really early on.

The following patch adds a knob to libc++,
_LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS, that can be set to disable
thread-unsafe functions that can easily be avoided in practice. The
following functions are not thread-safe:

- <clocale>: locale handles should be preferred over setlocale().
- <cstdlib>: mbrlen(), mbrtowc() and wcrtomb() should be preferred over
  their non-restartable counterparts.
- <ctime>: asctime(), ctime(), gmtime() and localtime() are not
  thread-safe. The first two are also deprecated by POSIX.

Differential Revision:	http://reviews.llvm.org/D8703
Reviewed by:	marshall

llvm-svn: 240527
2015-06-24 08:44:38 +00:00
Howard Hinnant 073458b1ab Windows support by Ruben Van Boxem.
llvm-svn: 142235
2011-10-17 20:05:10 +00:00
Howard Hinnant 412dbebe1b license change
llvm-svn: 119395
2010-11-16 22:09:02 +00:00
Howard Hinnant 5b08a8a432 Wiped out some non-ascii characters that snuck into the copyright.
llvm-svn: 103516
2010-05-11 21:36:01 +00:00
Howard Hinnant 3e519524c1 libcxx initial import
llvm-svn: 103490
2010-05-11 19:42:16 +00:00