[GitHub] [nuttx] xiaoxiang781216 commented on pull request #8121: arch:xtensa:toolchain: add -Wno-atmoic-alignment flags

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xiaoxiang781216 commented on PR #8121:
URL: https://github.com/apache/nuttx/pull/8121#issuecomment-1396564883

   > @xiaoxiang781216 Could you please share the motivation for disabling this warning? In which scenario does it manifest?
   
   @gustavonihei here is the warning generated by Candance's clang:
   ```
   [2023-01-19T07:31:49.594Z] media_proxy.c:498:9: error: large atomic operation may incur significant performance penalty [-Werror,-Watomic-alignment]
   [2023-01-19T07:31:49.594Z]     if (atomic_load(&priv->refs) == 1 && priv->socket) {
   [2023-01-19T07:31:49.594Z]         ^
   ```
   
   Here is the related struct definition:
   ```
   typedef struct MediaProxyPriv {
       void                  *proxy;
       char                  *cpu;
       uint64_t              handle;
       atomic_int            refs;
       int                   socket;
       void                  *cookie;
       media_event_callback  event;
   } MediaProxyPriv;
   ```
   The warning looks wrong since refs should be naturally alignment.
   
   > 
   > From this Clang patchset, this warning seems useful: https://reviews.llvm.org/D45319
   > 
   > > If an atomic variable is misaligned Clang will emit accesses to it as a libcall. These calls are likely to be slow and involve locks; they are almost certainly not what the developer intended.
   


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