On Sun, Feb 25, 2024 at 04:34:47PM +0200, Heikki Linnakangas wrote:
> I agree with Andres though, that unless someone raises their hand and
> volunteers to properly maintain the AIX support, we should drop it.
There's no way forward in which AIX support stops doing net harm. Even if AIX
enthusiasts intercepted would-be buildfarm failures and fixed them before
buildfarm.postgresql.org could see them, the damage from the broader community
seeing the AIX-specific code would outweigh the benefits of AIX support. I've
now disabled the animals for v17+, though each may do one more run before
picking up the disable.
My upthread observation about xcoff section alignment was a red herring. gcc
populates symbol-level alignment, and section-level alignment is unnecessary
if symbol-level alignment is correct. The simplest workaround for $SUBJECT
AIX failure would be to remove the "const", based on the results of the
attached test program. The pg_prewarm.c var is like al4096_static in the
outputs below, hence the lack of trouble there. The bulk_write.c var is like
al4096_static_const_initialized.
==== gcc 8.3.0
al4096 4096 @ 0x11000c000 (mod 0)
al4096_initialized 4096 @ 0x110000fd0 (mod 4048 - BUG)
al4096_const 4096 @ 0x11000f000 (mod 0)
al4096_const_initialized 4096 @ 0x10000cd00 (mod 3328 - BUG)
al4096_static 4096 @ 0x110005000 (mod 0)
al4096_static_initialized 4096 @ 0x110008000 (mod 0)
al4096_static_const 4096 @ 0x100000c10 (mod 3088 - BUG)
al4096_static_const_initialized 4096 @ 0x100003c10 (mod 3088 - BUG)
==== xlc 12.01.0000.0000
al4096 4096 @ 0x110008000 (mod 0)
al4096_initialized 4096 @ 0x110004000 (mod 0)
al4096_const 4096 @ 0x11000b000 (mod 0)
al4096_const_initialized 4096 @ 0x100007000 (mod 0)
al4096_static 4096 @ 0x11000e000 (mod 0)
al4096_static_initialized 4096 @ 0x110001000 (mod 0)
al4096_static_const 4096 @ 0x110011000 (mod 0)
al4096_static_const_initialized 4096 @ 0x1000007d0 (mod 2000 - BUG)
==== ibm-clang 17.1.1.2
al4096 4096 @ 0x110001000 (mod 0)
al4096_initialized 4096 @ 0x110004000 (mod 0)
al4096_const 4096 @ 0x100001000 (mod 0)
al4096_const_initialized 4096 @ 0x100005000 (mod 0)
al4096_static 4096 @ 0x110008000 (mod 0)
al4096_static_initialized 4096 @ 0x11000b000 (mod 0)
al4096_static_const 4096 @ 0x100009000 (mod 0)
al4096_static_const_initialized 4096 @ 0x10000d000 (mod 0)
#include <stdio.h>
#include <stdint.h>
/* add a byte so the compiler has to go out of its way to achieve alignment for
consecutive instances */
typedef union PGIOAlignedBlock
{
__attribute__((aligned(4096)))
char data[1 + 8192];
double force_align_d;
uint64_t force_align_i64;
} PGIOAlignedBlock;
char pad;
/* with and without each of: static, const, initializer */
PGIOAlignedBlock al4096;
PGIOAlignedBlock al4096_initialized = {{0}};
const PGIOAlignedBlock al4096_const;
const PGIOAlignedBlock al4096_const_initialized = {{0}};
static PGIOAlignedBlock al4096_static;
static PGIOAlignedBlock al4096_static_initialized = {{0}};
static const PGIOAlignedBlock al4096_static_const;
static const PGIOAlignedBlock al4096_static_const_initialized = {{0}};
/* in case last position is special */
static const PGIOAlignedBlock last;
static const PGIOAlignedBlock last_initialized = {{0}};
#define DUMP(want_align, var) dump_internal(#var, (want_align), &(var))
static void
dump_internal(const char *ident, unsigned want_align, const void *addr)
{
unsigned mod = (uintptr_t) addr % want_align;
printf("%-32s %4u @ 0x%p (mod %u%s)\n", ident, want_align, addr,
mod, mod ? " - BUG" : "");
}
int
main(int argc, char **argv)
{
DUMP(4096, al4096);
DUMP(4096, al4096_initialized);
DUMP(4096, al4096_const);
DUMP(4096, al4096_const_initialized);
DUMP(4096, al4096_static);
DUMP(4096, al4096_static_initialized);
DUMP(4096, al4096_static_const);
DUMP(4096, al4096_static_const_initialized);
return 0;
}
