[pull] master from libretro:master#977
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pull[bot] merged 2 commits intoAlexandre1er:masterfrom Apr 29, 2026
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…AX init" This reverts commit 1a13965.
A header-only API exposing acquire/release atomic loads, stores and
acq_rel fetch_add/fetch_sub for int and size_t, with a backend cascade
that picks the best primitive each toolchain offers:
1. C11 <stdatomic.h> - modern GCC/Clang/MSVC at -std=c11
2. C++11 <atomic> - C++ TUs at -std=c++11 or _MSVC_LANG
>= 201103L
3. GCC __atomic_* - GCC 4.7+ / Clang 3.1+
(Clang impersonates GCC 4.2 in
__GNUC__, so the gate uses
defined(__clang__) || version check
to avoid falling through to __sync)
4. MSVC Win32 Interlocked* - VS2003+, OG Xbox, Xbox 360 XDK; on
ARM/ARM64 the plain forms lack
barriers (PostgreSQL hit this on
Win11/ARM64 in 2025), so RMWs are
bracketed with __dmb on those targets
5. Apple OSAtomic* - PPC / pre-10.7 fallback
6. GCC __sync_* - GCC 4.1-4.6
7. volatile fallback - last resort, single-core / x86 TSO
only; emits a #warning unless
suppressed
Capability flags exposed to callers:
HAVE_RETRO_ATOMIC always defined after include
RETRO_ATOMIC_LOCK_FREE defined iff a real backend selected
(NOT for the volatile fallback)
RETRO_ATOMIC_BACKEND_NAME string literal, for diagnostics
RETRO_ATOMIC_REQUIRE_LOCK_FREE caller-side opt-in: setting this
before include turns the volatile
fallback into a #error
No active TU includes the header yet; it is the foundation for a future
SPSC fifo primitive and consolidates the hand-rolled atomic shims
currently scattered across coreaudio*.c/m, xaudio.c, mmdevice_common.c,
opensl.c, and gfx_thumbnail.c.
Sample: libretro-common/samples/atomic/retro_atomic_test/
Single-threaded property checks of every macro plus a 1M-iteration
SPSC stress test (when HAVE_THREADS) using rthreads sthread_create.
Compile-time #error checks assert that every named real backend
implies RETRO_ATOMIC_LOCK_FREE and that the volatile fallback never
sets it.
CI: Linux-libretro-common-samples.yml
- retro_atomic_test added to the native run allowlist (gcc, with
the workflow's default ASan/UBSan)
- new step: C++ smoke test compiled with both g++ and clang++ at
-std=c++11/14/17 against the in-tree header
- new step: retro_atomic_test built with clang -fsanitize=thread and
run with TSAN_OPTIONS=halt_on_error=1; TSan instruments every
atomic load/store and would flag a missing barrier in the SPSC
stress that x86 TSO would otherwise hide
- new job: retro-atomic-cross, matrix [aarch64, armv7], cross-compiles
with gcc-aarch64-linux-gnu / gcc-arm-linux-gnueabihf, runs the
binary under qemu-user-static, and grep-inspects the emitted asm
for ldar/stlr/ldadd*_acq_rel (aarch64) or dmb/ldrex/strex (armv7);
the inspect step exits 1 if no barrier mnemonics are found, which
catches a silent regression to the volatile fallback
Verified locally:
- x86_64 native (gcc, clang) + ASan/UBSan + TSan
- AArch64 cross-compile + qemu, asm shows ldar/stlr/ldadd*_acq_rel
- ARMv7 cross-compile + qemu, asm shows dmb/ldrex/strex
- MIPSel cross-compile + qemu, asm shows ll/sc/sync
- C++11/14/17/20 native (g++ and clang++)
- C++98 (g++ and clang++) correctly falls through to GCC __atomic_*
- All 9 forced-backend shape tests (C11, GCC __atomic_*, __sync_*,
volatile, MSVC x86/x64/ARM64 mocked, Apple 32/64 mocked) plus
forced C++11
Not verified on real hardware:
- MSVC ARM64 (correct by construction from MS docs and PostgreSQL
precedent; awaits Windows-on-ARM CI)
- Real PowerPC SMP (Wii U, Xbox 360); reasoned from devkitPPC GCC
and Microsoft's Xbox 360 lockless guide
- __sync_* and Apple OSAtomic backends (dead code on every current
target; selection requires GCC < 4.7 or pre-10.7 Apple)
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