On 2021-02-28 13:31, Hans-Peter Nilsson wrote:

On Fri, 26 Feb 2021, Thiago Macieira via Gcc-patches wrote:

On Friday, 26 February 2021 11:31:00 PST Andreas Schwab wrote: On Feb 26 2021, Thiago Macieira wrote: On Friday, 26 February 2021 10:14:42 PST Andreas Schwab wrote: On Feb 26 2021, Thiago Macieira via Gcc-patches wrote: - alignas(__alignof__(ptrdiff_t)) ptrdiff_t _M_a;
+    alignas(__alignof__(int)) int _M_a;
Futexes must be aligned to 4 bytes.

Agreed, but doesn't this accomplish that?
No.  It uses whatever alignment the type already has, and is an
elaborate no-op.
I thought so too when I read the original line. But I expected it was written like that for a reason, especially since the same pattern appears in other
places.

I can change to "alignas(4)" (which is a GCC extension, I believe). Is that
the correct solution?
IMNSHO make use of the corresponding atomic type.  Then there'd
be no need for separate what's-the-right-align-curse games.

There is no predicate wait on atomic<T>.

brgds, H-P

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