On 15.03.2024 01:21, Stefano Stabellini wrote: > On Mon, 11 Mar 2024, Julien Grall wrote: >> On 11/03/2024 11:32, George Dunlap wrote: >>> On Sat, Mar 9, 2024 at 1:59 AM Stefano Stabellini >>> <sstabell...@kernel.org> wrote: >>>> >>>> I would like to resurrect this thread and ask other opinions. >>>> >>>> >>>> On Thu, 23 Nov 2023, Jan Beulich wrote: >>>>> On 22.11.2023 22:46, Stefano Stabellini wrote: >>>>>> Two out of three do_multicall definitions/declarations use uint32_t as >>>>>> type for the "nr_calls" parameters. Change the third one to be >>>>>> consistent with the other two. >>>>>> >>>>>> Link: >>>>>> https://lore.kernel.org/xen-devel/7e3abd4c0ef5127a07a60de1bf090a8aefac8e5c.1692717906.git.federico.seraf...@bugseng.com/ >>>>>> Link: >>>>>> https://lore.kernel.org/xen-devel/alpine.DEB.2.22.394.2308251502430.6458@ubuntu-linux-20-04-desktop/ >>>>>> Signed-off-by: Stefano Stabellini <stefano.stabell...@amd.com> >>>>>> --- >>>>>> Note that a previous discussion showed disagreement between >>>>>> maintainers >>>>>> on this topic. The source of disagreements are that we don't want to >>>>>> change a guest-visible ABI and we haven't properly documented how to >>>>>> use >>>>>> types for guest ABIs. >>>>>> >>>>>> As an example, fixed-width types have the advantage of being explicit >>>>>> about their size but sometimes register-size types are required (e.g. >>>>>> unsigned long). The C specification says little about the size of >>>>>> unsigned long and today, and we even use unsigned int in guest ABIs >>>>>> without specifying the expected width of unsigned int on the various >>>>>> arches. As Jan pointed out, in Xen we assume sizeof(int) >= 4, but >>>>>> that's not written anywhere as far as I can tell. >>>>>> >>>>>> I think the appropriate solution would be to document properly our >>>>>> expectations of both fixed-width and non-fixed-width types, and how to >>>>>> use them for guest-visible ABIs. >>>>>> >>>>>> In this patch I used uint32_t for a couple of reasons: >>>>>> - until we have better documentation, I feel more confident in using >>>>>> explicitly-sized integers in guest-visible ABIs >>>>> >>>>> I disagree with this way of looking at it. Guests don't invoke these >>>>> functions directly, and our assembly code sitting in between already is >>>>> expected to (and does) guarantee that (in the case here) unsigned int >>>>> would be okay to use (as would be unsigned long, but at least on x86 >>>>> that's slightly less efficient), in line with what ./CODING_STYLE says. >>>>> >>>>> Otoh structure definitions in the public interface of course need to >>>>> use fixed with types (and still doesn't properly do so in a few cases). >>> >>> You didn't address the other argument, which was that all the other >>> definitions have uint32_t; in particular, >>> common/multicall.c:do_multicall() takes uint32_t. Surely that should >>> match the non-compat definition in include/hypercall-defs.c? >>> >>> Whether they should both be `unsigned int` or `uint32_t` I don't >>> really feel like I have a good enough grasp of the situation to form a >>> strong opinion. >> >> FWIW +1. We at least need some consistency. > > Consistency is my top concern. Let's put the "unsigned int" vs > "uint32_t" argument aside. > > do_multicall is not consistent with itself. We need > hypercall-defs.c:do_multicall and multicall.c:do_multicall to match. > > Option1) We can change hypercall-defs.c:do_multicall to use uint32_t. > > Option2) Or we can change multicall.c:do_multicall to use unsigned int. > > I went with Option1. Andrew expressed his strong preference toward > Option1 in the past. George seems to prefer Option1. > > Jan, can you accept Option1 and move on?
Counter question: Why do we have the opposite of what you all want stated in ./CODING_STYLE? Looking at the commit, it was actually George who ack-ed it. I can accept option 1 if ./CODING_STYLE is first changed / amended. Jan
