[v7,0/4] _FORTIFY_SOURCE=3

  This patchset implements a new fortification level, _FORTIFY_SOURCE=3.
This level allows size information to be dynamic, which may potentially
have a noticeable performance impact.  It uses the
__builtin_dynamic_object_size builtin available in clang to expand
coverage of fortifications at the expense of some performance.

Patch 1/4 adds a warning on unsupported _FORTIFY_LEVEL values.  This
change can go in independently of the new fortification level.

Patch 2/4 adds the macro scaffolding to allow the new _FORTIFY_SOURCE
level and to select the __builtin_dynamic_object_size builtin when it is
available.

Patch 3/4 adds support for string functions; these functions have
additional fortified builtins of the form __builtin___func_chk.

Patch 4/4 adds support for non-string functions that are
fortification-ready for levels 1 and 2.

Testing:

The glibc testsuite doesn't directly support clang at the moment, so
having tests in the glibc source tree is pointless as long as gcc does
not have support for __builtin_dynamic_object_size.  There is a separate
project on GitHub called fortify-test-suite[1] that houses fortification
tests and is capable of testing multiple levels of fortification with
multiple compilers.  I have proposed a PR[2] to add support for
_FORTIFY_SOURCE=3 and have verified my changes with those tests.

Those tests run clean for clang when run with these changes and PR[2]
and they fail at level 3 for gcc, as expected.

[1] https://github.com/serge-sans-paille/fortify-test-suite
[2] https://github.com/serge-sans-paille/fortify-test-suite/pull/9

Changes since last version of the patchset:

- Split out patches as suggested during review
- Renamed __objsize to __glibc_objsize

Siddhesh Poyarekar (4):
  Warn on unsupported fortification levels
  Introduce _FORTIFY_SOURCE=3
  string: Enable __FORTIFY_LEVEL=3
  nonstring: Enable __FORTIFY_LEVEL=3

 NEWS                            |   6 ++
 include/features.h              |   8 ++
 include/string.h                |   5 +-
 io/bits/poll2.h                 |  18 ++--
 libio/bits/stdio.h              |   2 +-
 libio/bits/stdio2.h             |  62 ++++++++------
 manual/creature.texi            |   3 +-
 misc/sys/cdefs.h                |   9 ++
 posix/bits/unistd.h             | 120 ++++++++++++++------------
 socket/bits/socket2.h           |  22 ++---
 stdlib/bits/stdlib.h            |  42 +++++----
 string/bits/string_fortified.h  |  29 ++++---
 string/bits/strings_fortified.h |   6 +-
 wcsmbs/bits/wchar2.h            | 146 ++++++++++++++++++--------------
 14 files changed, 279 insertions(+), 199 deletions(-)