Re: standards/52571 (max_align_t has smaller alignment than double)

[riastradh%NetBSD.org@localhost]

Synopsis: max_align_t has smaller alignment than double

State-Changed-From-To: open->closed
State-Changed-By: riastradh%NetBSD.org@localhost
State-Changed-When: Mon, 09 Sep 2024 11:44:47 +0000
State-Changed-Why:
This is a bizarre quirk of gcc's __alignof__ extension, not NetBSD's
fault.  Use the standard _Alignof instead.  For example, compare the
sizes of symbols from the following definitions:

char gcc_alignof_double[__alignof__(double)];
char gcc_alignof_uniondouble[__alignof__(union { double x; })];
char stdc_alignof_double[_Alignof(double)];
char stdc_alignof_uniondouble[_Alignof(union { double x; })];

When I compile this with i386 gcc -std=c11 and dump the symbols with
`readelf -s', I get:

   Num:    Value  Size Type    Bind   Vis      Ndx Name
...
     2: 00000000     8 OBJECT  GLOBAL DEFAULT    3 gcc_alignof_double
     3: 00000008     4 OBJECT  GLOBAL DEFAULT    3 gcc_alignof_uniondouble
     4: 0000000c     4 OBJECT  GLOBAL DEFAULT    3 stdc_alignof_double
     5: 00000010     4 OBJECT  GLOBAL DEFAULT    3 stdc_alignof_uniondouble

Whatever gcc's __alignof__ gives you is not the required alignment: if
it were, it would have to agree with the plain double and the
union-of-double cases, but it doesn't.