projects / mirror_qemu.git / blame
| Commit | Line | Data |
|---|---|---|
| e6cd4bb5 RH |
1 | /* |
| 2 | * Simple interface for 128-bit atomic operations. | |
| 3 | * | |
| 4 | * Copyright (C) 2018 Linaro, Ltd. | |
| 5 | * | |
| 6 | * This work is licensed under the terms of the GNU GPL, version 2 or later. | |
| 7 | * See the COPYING file in the top-level directory. | |
| 8 | * | |
| 29f23167 | 9 | * See docs/devel/atomics.rst for discussion about the guarantees each |
| e6cd4bb5 RH |
10 | * atomic primitive is meant to provide. |
| 11 | */ | |
| 12 | ||
| 13 | #ifndef QEMU_ATOMIC128_H | |
| 14 | #define QEMU_ATOMIC128_H | |
| 15 | ||
| ec150c7e MA |
16 | #include "qemu/int128.h" |
| 17 | ||
| 333c813b RH |
18 | /* |
| 19 | * If __alignof(unsigned __int128) < 16, GCC may refuse to inline atomics | |
| 20 | * that are supported by the host, e.g. s390x. We can force the pointer to | |
| 21 | * have our known alignment with __builtin_assume_aligned, however prior to | |
| 22 | * GCC 13 that was only reliable with optimization enabled. See | |
| 23 | * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107389 | |
| 24 | */ | |
| 25 | #if defined(CONFIG_ATOMIC128_OPT) | |
| 26 | # if !defined(__OPTIMIZE__) | |
| 27 | # define ATTRIBUTE_ATOMIC128_OPT __attribute__((optimize("O1"))) | |
| 28 | # endif | |
| 29 | # define CONFIG_ATOMIC128 | |
| 30 | #endif | |
| 31 | #ifndef ATTRIBUTE_ATOMIC128_OPT | |
| 32 | # define ATTRIBUTE_ATOMIC128_OPT | |
| 33 | #endif | |
| 34 | ||
| e6cd4bb5 RH |
35 | /* |
| 36 | * GCC is a house divided about supporting large atomic operations. | |
| 37 | * | |
| 38 | * For hosts that only have large compare-and-swap, a legalistic reading | |
| 39 | * of the C++ standard means that one cannot implement __atomic_read on | |
| 40 | * read-only memory, and thus all atomic operations must synchronize | |
| 41 | * through libatomic. | |
| 42 | * | |
| 43 | * See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80878 | |
| 44 | * | |
| 45 | * This interpretation is not especially helpful for QEMU. | |
| 7893e42d PMD |
46 | * For system-mode, all RAM is always read/write from the hypervisor. |
| 47 | * For user-mode, if the guest doesn't implement such an __atomic_read | |
| e6cd4bb5 RH |
48 | * then the host need not worry about it either. |
| 49 | * | |
| 50 | * Moreover, using libatomic is not an option, because its interface is | |
| 51 | * built for std::atomic<T>, and requires that *all* accesses to such an | |
| 52 | * object go through the library. In our case we do not have an object | |
| 53 | * in the C/C++ sense, but a view of memory as seen by the guest. | |
| 54 | * The guest may issue a large atomic operation and then access those | |
| 55 | * pieces using word-sized accesses. From the hypervisor, we have no | |
| 56 | * way to connect those two actions. | |
| 57 | * | |
| 58 | * Therefore, special case each platform. | |
| 59 | */ | |
| 60 | ||
| 412db3d5 | 61 | #include "host/atomic128-cas.h" |
| 15469133 | 62 | #include "host/atomic128-ldst.h" |
| e6cd4bb5 RH |
63 | |
| 64 | #endif /* QEMU_ATOMIC128_H */ |