This fixes deprecation warnings when building for macOS >= 10.12 systems.
Additionally, using stdatomic.h (or the more modern __atomic_ builtins)
is required when targeting CHERI-enabled architectures such as
CHERI-RISC-V or Arm's Morello since the compiler rejects __sync_* atomic
for pointer types (they only work with integers).
Reverts the part of 6def66164a that
removed the fc_atomic_ptr_cmpexch compatibility code for systems earlier
than Mac OS X 10.5.
Reverts the part of 447b9ccc7d that moved
the definition of fc_atomic_ptr_get into the Mac OS X > 10.4 block. That
code is still needed on 10.4 and is implemented using functions that are
available on 10.4.
Compare against MAC_OS_X_VERSION_MIN_REQUIRED using a number not a
constant because the constant is not available on earlier SDKs.
Before this change building with ThreadSanitizer and running
test/test-pthread generated a large number of threading issues. These
mostly stemmed from fc_atomic_ptr_get not doing an atomic load and using
"acquire load" instead of "load acquire". After making these changes it
was still necessary to use fc_atomic_ptr_get where it was needed.
This also documents the current memory barrier requirements for the
atomic primitives.
iPhone 2.1 was released a long time ago, and the macro for checking
the target iOS SDK version has changed. We can simplify everything and
do a very basic check.
Alex Richardson
Ryan Schmidt
Ben Wagner
Akira TAGOH
Nirbheek Chauhan
Behdad Esfahbod