[DPDK/core Bug 1425] enable_stdatomic=true breaks C++ on GCC 11 and earlier

[Tyler Retzlaff]

On Mon, Apr 29, 2024 at 06:21:13AM +0000, bugzilla at dpdk.org wrote:
> https://bugs.dpdk.org/show_bug.cgi?id=1425
> 
>             Bug ID: 1425
>            Summary: enable_stdatomic=true breaks C++  on GCC 11 and
>                     earlier
>            Product: DPDK
>            Version: 23.11
>           Hardware: All
>                 OS: Linux
>             Status: UNCONFIRMED
>           Severity: normal
>           Priority: Normal
>          Component: core
>           Assignee: dev at dpdk.org
>           Reporter: mattias.ronnblom at ericsson.com
>   Target Milestone: ---
> 
> On GCC 11 and earlier, configuring enable_stdatomic=true prevents the use of
> all DPDK header files that directly or indirectly include <rte_stdatomic.h>
> from a C++ translation unit (e.g., app).
> 
> <rte_stdatomic.h> includes <stdatomic.h>, which in turn is not necessarily
> C++-compatible.

This is known but to add some information.

C++ and enable_stdatomic=true for llvm and gcc are not currently
supported. the combination will remain unsupported for C++ compilers
that do not support -std=c++23 which is the first C++ standard that
requires interoperability with C11 stdatomic.h

When enable_stdatomic=true there are bugs/incorrect usages of atomic
qualifier in casts that (even when using C++23) cause compilation
failure. These are a fixable but are low priority without -std=c++23.

Finally, the legacy atomics remain unconverted to stdatomic. This will
cause enable_stdatomic=true not to build when using llvm (but not gcc)
because llvm strictly enforces qualification when using atomic generics.

> 
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