Re: [PATCH] Add native windows on arm64 support

On Sat, 28 Sept 2024 at 20:03, Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:

> On Tue, Feb 13, 2024 at 10:01 AM Dave Cramer <davecramer(at)postgres(dot)rocks>
> wrote:
> > > postgres.exe!dsa_free(dsa_area * area, unsigned __int64 dp) Line 869 C
> > postgres.exe!resize(dshash_table * hash_table, unsigned __int64
> new_size_log2) Line 879 C
> > postgres.exe!dshash_find_or_insert(dshash_table * hash_table, const
> void * key, bool * found) Line 480 C
> > postgres.exe!pgstat_get_entry_ref(PgStat_Kind kind, unsigned int
> dboid, unsigned int objoid, bool create, bool * created_entry) Line 455 C
>
> Hmm, we can see that the spinlock stuff is too weak (assumes TSO), but
> there aren't any spinlocks near that code so I think something else is
> wrong. What does pg_read_barrier() compile to? I mention that
> because it's used near there in a somewhat complicated way. But I'm a
> bit confused because by reading through the code it looks like it
> should be too strong, not too weak. I think it should fall back to
> pg_memory_barrier_impl() for lack of pg_read_barrier_impl(), which
> should produce MemoryBarrier() and I guess DMB SY (ARM instruction for
> full system data memory barrier). So maybe some other pg_atomic_XXX
> operations are falling back to code that doesn't work.
>
> Just for experimentation, you could see what happens if you redirect
> all that stuff to C11's <stdatomic.h>. Here's a quick-and-dirty patch
> for that, which works on my ARM Mac, but I have no idea if it'll work
> on MSVC (our CI uses MSVC 2019; they only added <stdatomic.h> in MSVC
> 2022, but that's the same edition that added ARM so you must have it).
> It's not a very finely tuned patch (for example I think several calls
> should use the _explicit() variants and be weaker, but they err on the
> side of being too strong, so the code they generate is probably not as
> fast as it could be; I lost interested when the general idea was
> rejected for now, but it might help learn something about the MSVC+ARM
> situation).
>
> Combined with the patch that redirects spinlocks to atomics[1], there
> would be no 'hand rolled' code relating to memory order or atomics,
> just standard modern C. There are obviously other architecture tests
> here and there, and some of them will be wrong (some of them are wrong
> already for MSVC on x86), and that might be fixed by project
> standardisation[2].
>
> [1]
> https://www.postgresql.org/message-id/CA%2BhUKGJ%2BoA%2B62iUZ-EQb5R2cAOW3Y942ZoOtzOD%3D1sQ05iNg6Q%40mail.gmail.com
> [2]
> https://www.postgresql.org/message-id/CA%2BhUKG%2BOu%2BC%2BpXioo_W1gKcwRCEN1WNrLBBPSMJyxjgc%2B1JEJA%40mail.gmail.com

Thomas,

Thanks, I will be able to try this when I get back from NY. So Thurs or so.

Dave