Horton

Re: alignas (C11)

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Eisentraut <peter@eisentraut.org>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2026-01-29T21:19:27Z
Lists: pgsql-hackers 
Peter Eisentraut <peter@eisentraut.org> writes:
> Well, in C11, alignas is itself a macro (defined to _Alignas).  I 
> suppose not in C++ though.  That seems too tricky, though.  I went with 
> your original proposal of disabling the affected typedefs on the 
> affected platform.  That seems safest.  These types aren't likely to be 
> used in extensions anyway, so this should have minimal practical impact.

I suspected that we'd have to supply the types as abstract structs
per my earlier suggestion, and just found a good reason why:
"headerscheck --cplusplus" is failing for me on RHEL8, because it
tries to parse all headers under C++.  This is blocking progress on
another patch, so I went ahead and committed the addition.

			regards, tom lane

Commits

  1. Further fix extended alignment for older g++.

  2. Disable extended alignment uses on older g++

  3. Work around buggy alignas in older g++

  4. Use C11 alignas in pg_atomic_uint64 definitions

  5. C11 alignas instead of unions -- extended alignments

  6. C11 alignas instead of unions

  7. Add <stdalign.h> to c.h