Re: git: 96acaa960023 - main - compat32: provide a type and a macro for (u)int64_t handling on non-x86 arches

On 20 Jan 2026, at 16:07, Konstantin Belousov <kostikbel@gmail.com> wrote:
> 
> On Tue, Jan 20, 2026 at 04:05:19PM +0000, Jessica Clarke wrote:
>> On 20 Jan 2026, at 14:42, Konstantin Belousov <kib@FreeBSD.org> wrote:
>>> 
>>> The branch main has been updated by kib:
>>> 
>>> URL: https://cgit.FreeBSD.org/src/commit/?id=96acaa960023c20e852e04e7cc5c6a5faca36c67
>>> 
>>> commit 96acaa960023c20e852e04e7cc5c6a5faca36c67
>>> Author:     Konstantin Belousov <kib@FreeBSD.org>
>>> AuthorDate: 2026-01-12 04:45:36 +0000
>>> Commit:     Konstantin Belousov <kib@FreeBSD.org>
>>> CommitDate: 2026-01-20 14:42:35 +0000
>>> 
>>>   compat32: provide a type and a macro for (u)int64_t handling on non-x86 arches
>>> 
>>>   uint64_t is 4-byte aligned on i386, but is 8-bytes aligned on all other
>>>   32bit arches FreeBSD supports.  Provide the freebsd32_uint64_t type and
>>>   the FU64_CP() macro, which are intended to be used where 32bit ABI uses
>>>   (u)int64_t type, and do proper layout and copying for the aggregate type.
>>> 
>>>   Reviewed by:    des, emaste
>>>   Sponsored by:   The FreeBSD Foundation
>>>   MFC after:      1 week
>>>   Differential revision:  https://reviews.freebsd.org/D54663
>>> ---
>>> sys/compat/freebsd32/freebsd32.h | 11 ++++++++++-
>>> sys/sys/abi_compat.h             |  8 ++++++++
>>> 2 files changed, 18 insertions(+), 1 deletion(-)
>>> 
>>> diff --git a/sys/compat/freebsd32/freebsd32.h b/sys/compat/freebsd32/freebsd32.h
>>> index 9d724c93fee7..7324f9adf70c 100644
>>> --- a/sys/compat/freebsd32/freebsd32.h
>>> +++ b/sys/compat/freebsd32/freebsd32.h
>>> @@ -36,8 +36,17 @@
>>> #include <sys/_ffcounter.h>
>>> 
>>> /*
>>> - * i386 is the only arch with a 32-bit time_t
>>> + * i386 is the only arch with a 32-bit time_t.
>>> + * Also it is the only arch with (u)int64_t having 4-bytes alignment.
>>> */
>>> +typedef struct {
>>> +#ifdef __amd64__
>>> + uint32_t val[2];
>>> +#else
>>> + uint64_t val;
>>> +#endif
>>> +} freebsd32_uint64_t;
>> 
>> Any reason not to use:
>> 
>>  typedef uint64_t freebsd32_uint64_t __aligned(4);
>> 
>> on amd64 (and normal typedef elsewhere)? Then you can just use the
>> normal CP. See for example https://godbolt.org/z/svseWv7xo.
> Yes, this way it uses only std C instead of the GNU extension, and not
> depend on compiler properly handle unaligned types.
> 
> IMO it is better that way, and all machinery is hidden under the typedef+
> the macro.

Well, except (a) the kernel uses GNU C for all manner of things already
(b) unaligned types are already well-supported otherwise packed structs
wouldn’t work, which we’re happy to use (c) your structure approach
hides less as you have to use the magic FU64_CP macro so is less
abstracted than my proposal.

Also, I just thought to check Linux, and it uses the same GNU C aligned
trick, so we’re in good company and any issues with it would show up
there, especially given people do use Clang to build Linux in
production these days.

So I disagree with your assessment entirely.

Jessica