[PATCH] eal: fix C++ builds when stdatomics is set
flat view
COOLING11d
From: Bruce Richardson <hidden>
Date: 2026-09-24 14:12:56
Subsystem:
library code, the rest · Maintainers:
Andrew Morton, Linus Torvalds
When the DPDK build is configured to use stdatomics rather than compiler
builtin atomics, the C++ chkincs builds were failing
In file included from buildtools/chkincs/staging/generic/rte_atomic.h:18,
from /home/morten/upstreaming/dpdk-stack-std/lib/eal/x86/include/rte_atomic.h:12,
from buildtools/chkincs/chkincs-cpp.p/rte_atomic.cpp:1:
buildtools/chkincs/staging/rte_stdatomic.h:30:9: error: ‘memory_order’ does not name a type
30 | typedef memory_order rte_memory_order;
| ^~~~~~~~~~~~
The cause is differences in atomics in C (C11) and C++ (e.g. C++17 as
supported by current GCC). As explained by AI analysis:
" _Atomic(T) is a C11 feature. In C++ mode, GCC 15 does not support it as
a type specifier, and <stdatomic.h> in C++17 doesn't expose
memory_order in the global namespace (that's only in C++23). DPDK
headers also use _Atomic in anonymous unions and under extern "C",
which are incompatible with C++'s std::atomic<T> mapping."
To fix this in a resilient manner we need to go from two blocks in
rte_atomic.h to three. We have the existing non-standard/builtin
atomics path, but the standard atomic path now needs to be split into C
compatible and C++ compatible blocks. This fixes the build issues with
C++ while keeping existing C builds unchanged.
Bugzilla ID: 1985
Fixes: 5c381a3587d1 ("eal: provide stdatomic API")
Cc: stable@dpdk.org
Signed-off-by: Bruce Richardson <redacted>
---
lib/eal/include/rte_stdatomic.h | 75 +++++++++++++++++++++++++++++++++
1 file changed, 75 insertions(+)
diff --git a/lib/eal/include/rte_stdatomic.h b/lib/eal/include/rte_stdatomic.h
index 7258b393f1..d31eb4bfab 100644
--- a/lib/eal/include/rte_stdatomic.h
+++ b/lib/eal/include/rte_stdatomic.h@@ -8,6 +8,8 @@ #include <assert.h> #ifdef RTE_ENABLE_STDATOMIC + +#ifndef __cplusplus #ifndef _MSC_VER #ifdef __STDC_NO_ATOMICS__ #error enable_stdatomic=true but atomics not supported by toolchain
@@ -114,6 +116,79 @@ static_assert(rte_memory_order_seq_cst == __ATOMIC_SEQ_CST, #define __rte_atomic_thread_fence(memorder) \ atomic_thread_fence(memorder) +#else /* __cplusplus */ + +/* C++ cannot use the C11 _Atomic member layout that DPDK public headers + * rely on, so keep the builtin-based implementation for C++ and continue + * to expose the existing rte_atomic_* API surface. + */ +#define RTE_ATOMIC(type) type + +#define __rte_atomic + +/* The memory order is an integer type in GCC built-ins, + * not an enumerated type like in C11. + */ +typedef int rte_memory_order; + +#define rte_memory_order_relaxed __ATOMIC_RELAXED +#define rte_memory_order_consume __ATOMIC_CONSUME +#define rte_memory_order_acquire __ATOMIC_ACQUIRE +#define rte_memory_order_release __ATOMIC_RELEASE +#define rte_memory_order_acq_rel __ATOMIC_ACQ_REL +#define rte_memory_order_seq_cst __ATOMIC_SEQ_CST + +#define rte_atomic_load_explicit(ptr, memorder) \ + __atomic_load_n(ptr, memorder) + +#define rte_atomic_store_explicit(ptr, val, memorder) \ + __atomic_store_n(ptr, val, memorder) + +#define rte_atomic_exchange_explicit(ptr, val, memorder) \ + __atomic_exchange_n(ptr, val, memorder) + +#define rte_atomic_compare_exchange_strong_explicit(ptr, expected, desired, \ + succ_memorder, fail_memorder) \ + __atomic_compare_exchange_n(ptr, expected, desired, 0, \ + succ_memorder, fail_memorder) + +#define rte_atomic_compare_exchange_weak_explicit(ptr, expected, desired, \ + succ_memorder, fail_memorder) \ + __atomic_compare_exchange_n(ptr, expected, desired, 1, \ + succ_memorder, fail_memorder) + +#define rte_atomic_fetch_add_explicit(ptr, val, memorder) \ + __atomic_fetch_add(ptr, val, memorder) + +#define rte_atomic_fetch_sub_explicit(ptr, val, memorder) \ + __atomic_fetch_sub(ptr, val, memorder) + +#define rte_atomic_fetch_and_explicit(ptr, val, memorder) \ + __atomic_fetch_and(ptr, val, memorder) + +#define rte_atomic_fetch_xor_explicit(ptr, val, memorder) \ + __atomic_fetch_xor(ptr, val, memorder) + +#define rte_atomic_fetch_or_explicit(ptr, val, memorder) \ + __atomic_fetch_or(ptr, val, memorder) + +#define rte_atomic_fetch_nand_explicit(ptr, val, memorder) \ + __atomic_fetch_nand(ptr, val, memorder) + +#define rte_atomic_flag_test_and_set_explicit(ptr, memorder) \ + __atomic_test_and_set(ptr, memorder) + +#define rte_atomic_flag_clear_explicit(ptr, memorder) \ + __atomic_clear(ptr, memorder) + +/* We provide internal macro here to allow conditional expansion + * in the body of the per-arch rte_atomic_thread_fence inline functions. + */ +#define __rte_atomic_thread_fence(memorder) \ + __atomic_thread_fence(memorder) + +#endif /* __cplusplus */ + #else /* !RTE_ENABLE_STDATOMIC */ #define RTE_ATOMIC(type) type
--
2.53.0