We have some potential race conditions vs our user-exec signal
handler that will be solved with this barrier.
Backports commit 359896dfa4e9707e1acea99129d324250fccab04 from qemu
ATOMIC_REG_SIZE is currently defined as the default sizeof(void *) for
all MIPS host builds, including those using the n32 ABI. n32 is the
MIPS64 ILP32 ABI and as such tcg/mips/tcg-target.h defines
TCG_TARGET_REG_BITS as 64 for n32 builds. If we attempt to build QEMU
for an n32 host with support for a 64b target architecture then
TCG_OVERSIZED_GUEST is 0 and accel/tcg/cputlb.c attempts to use
atomic_* functions. This fails because ATOMIC_REG_SIZE is 4, causing
the calls to QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE) in the
various atomic_* functions to generate errors.
Fix this by defining ATOMIC_REG_SIZE as 8 for all MIPS64 builds, which
will cover both n32 (ILP32) & n64 (LP64) ABIs in much the same was as
we already do for x86_64/x32.
Backports commit c5b00c1684f3317e887c7401b58dde54c2b05354 from qemu
Some versions of gcc produce a spurious warning if the result of
__atomic_compare_echange_n() is not used and the type involved
is a signed 8 bit value:
error: value computed is not used [-Werror=unused-value]
This has been seen on at least
gcc (Ubuntu 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609
Work around this by using an explicit cast to void to indicate
that we don't care about the return value.
We don't currently use our atomic_cmpxchg() macro on any signed
8 bit types, but the upcoming support for the Arm v8.1-Atomics
will require it.
Backports commit cd95fc28fb6d8afced0d70ce52c294d0761a9daa from qemu
We need to coordinate with the TCG_OVERSIZED_GUEST test in cputlb.c,
and allow 64-bit atomics even though sizeof(void *) == 4.
Backports commit 374aae653499f4d405caf32b7fff0c8639113fe4 from qemu
Add all of cmpxchg, op_fetch, fetch_op, and xchg.
Handle both endian-ness, and sizes up to 8.
Handle expanding non-atomically, when emulating in serial.
Backports commit c482cb117cc418115ca9c6d21a7a2315414c0a40 from qemu
While the check against sizeof(void *) is appropriate for
normal usage within qemu, there are places in which we want
wider operaions and have checked for their existance.
Backports commit 84bca3927b36fb1d9a2ca85cbbdf9023d2b84678 from qemu
Making these functional rather than object macros will
prevent later problems with complex macro expansion.
Backports commit d1a9f2d12fcfc942924956fbe321aedf4226ccb7 from qemu
This introduces load-acquire and store-release operations in QEMU.
For now, just use them as an implementation detail of atomic_mb_read
and atomic_mb_set.
Since docs/atomics.txt documents that atomic_mb_read only synchronizes
with an atomic_mb_set of the same variable, we can use the new implementation
everywhere instead of seq-cst loads and stores.
Backports commit 803cf26a9e019b5d2256a8edeb22e3538c4f3261 from qemu
Only very modern GCC's actually set this define when building with the
ThreadSanitizer so this little typo slipped though.
Backports commit 23ea7f57949f2f5934f4d5bbc29fe321b3a7067b from qemu
Add some notes on the use of the relaxed atomic access helpers and their
importance for defined behaviour in C11's multi-threaded memory model.
Backports commit e653bc6b0ff645c25b8a2eb607c18a5c98b59db6 from qemu
Use the __atomic_*_n() primitives which take the value as argument. It
is not necessary to store the value locally before calling the
primitive, hence saving us a stack store and load.
Backports commit 89943de17c4e276f2c47f05b4604e8816a6a636c from qemu
Currently we emit a consume-load in atomic_rcu_read. Because of
limitations in current compilers, this is overkill for non-Alpha hosts
and it is only useful to make Thread Sanitizer work.
This patch leaves the consume-load in atomic_rcu_read when
compiling with Thread Sanitizer enabled, and resorts to a
relaxed load + smp_read_barrier_depends otherwise.
On an RMO host architecture, such as aarch64, the performance
improvement of this change is easily measurable. For instance,
qht-bench performs an atomic_rcu_read on every lookup. Performance
before and after applying this patch:
$ tests/qht-bench -d 5 -n 1
Before: 9.78 MT/s
After: 10.96 MT/s
Backports commit 15487aa132109891482f79d78a30d6cfd465a391 from qemu
For correctness, smp_read_barrier_depends() is only required to
emit a barrier on Alpha hosts. However, we are currently emitting
a consume fence unconditionally, and most compilers currently treat
consume and acquire fences as equivalent.
Fix it by keeping the consume fence if we're compiling with Thread
Sanitizer, since this might help prevent false warnings. Otherwise,
only emit the barrier for Alpha hosts. Note that we still guarantee
that smp_read_barrier_depends() is a compiler barrier.
Backports commit c983895258a771f8a5e4a53950bfb7fd2216651c from qemu
The __atomic primitives have been available since GCC 4.7 and provide
a richer interface for describing memory ordering requirements. As a
bonus by using the primitives instead of hand-rolled functions we can
use tools such as the ThreadSanitizer which need the use of well
defined APIs for its analysis.
If we have __ATOMIC defines we exclusively use the __atomic primitives
for all our atomic access. Otherwise we fall back to the mixture of
__sync and hand-rolled barrier cases.
Backports commit a0aa44b488b3601415d55041e4619aef5f3a4ba8 from qemu
__atomic_thread_fence does not include a compiler barrier; in the
C++11 memory model, fences take effect in combination with other
atomic operations. GCC implements this by making __atomic_load and
__atomic_store access memory as if the pointer was volatile, and
leaves no trace whatsoever of acquire and release fences in the
compiler's intermediate representation.
In QEMU, we want memory barriers to act on all memory, but at the same
time we would like to use __atomic_thread_fence for portability reasons.
Add compiler barriers manually around the __atomic_thread_fence.
Backports commit 3bbf572345c65813f86a8fc434ea1b23beb08e16 from qemu
* unicorn: use waitable timer to implement usleep() on Windows
Signed-off-by: vardyh <vardyh.dev@gmail.com>
* atomic: implement barrier() for msvc
Signed-off-by: vardyh <vardyh.dev@gmail.com>
