Messages in this thread | | | Subject | Re: [PATCH v4 00/24] ILP32 for ARM64 | From | "Dr. Philipp Tomsich" <> | Date | Fri, 17 Apr 2015 17:15:46 +0200 |
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More comments below.
> On 17 Apr 2015, at 16:46, Catalin Marinas <catalin.marinas@arm.com> wrote: > > Even in this case, we could enable AArch32 compat knowing that ioctls > wouldn't work. If this is important, we can add an option to enable > ioctl support for ILP32 and re-target the asm/compat.h definitions. > >> g) create a new ABI that does things in exactly the way that we >> would use as the native syscall interface if we had an ilp32 >> kernel running on aarch64 with the asm-generic/unistd.h. >> This would mean a 32-bit __kernel_long_t and time_t, but extending >> time_t in the long run, together with aarch32 and i386. >> This one is particularly interesting for people that are interested >> in maximum posix compliance and in having a "nice" ABI, in particular >> if there is a slight chance that within the next decade we have >> reason to support building an arch/arm64 kernel itself in >> aarch64-ilp32 mode.
I don’t believe that an ILP32 kernel wouldn’t use an uint64_t for time_t, as it has full support for 64bit arithmetic anyway. I also believe that other kernel internals (e.g. filesystems and inode-numbering) would use native 64bit types.
The differences on the kernel side would mainly rest in that only a 32bit address space could reasonably be managed. So a native ILP32 ABI would differ from the LP64 ABI mainly in how sizeof(long) is represented in the user-space.
In other works: a native ILP32 ABI on an ILP32 kernel would have a 64bit time_t.
>>>> However, it would be nice to get agreement on the normal 32-bit ABI >>>> for time_t and timespec first, and then use the same thing everywhere. >>> >>> Do you mean for native 32-bit architectures? I think OpenBSD uses a >>> 64-bit time_t already on 32-bit arches, it's doable in Linux as well. >> >> Yes, and I'm working on that for Linux. The first step involves fixing >> the kernel, one file at a time, changing all users of time_t to use >> some other type (ktime_t or time64_t in most cases) instead, and introducing >> additional system calls to handle the boundary to user space without >> breaking stuff. See my presentation at http://elinux.org/ELC_2015_Presentations >> for more detail. > > The approach here is primarily to fix the problem for existing 32-bit > architectures by adding a new syscall and that's fine. But what if we > enforce 64-bit time_t for all _new_ architectures?
This boils down to whether we can define all the new syscalls _right now_ and get the new (extended) compat-layer set up. In this case we could have a userspace implementation that already conforms to this for ILP32.
Otherwise, we can just put a (MIPS64) N32-alike (AArch64) ILP32 in and migrate with everyone else.
Although it feels wrong to add another ABI that has a known limitation, this may in fact be the easiest way, as any fix to ILP32 would be done together with the fixes to all other 32bit ABIs.
So, while I would like to have a 64bit time_t for ILP32 based on principle, I do see the 32bit time_t path as the most pragmatic way forward… especially, as this unlinks getting “some form of” ILP32 merged from resolving the 64bit time_t issue across all architectures.
Phil.
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