On Monday 18 May 2015 17:03:08 Thorsten Glaser wrote:
MIPS on the other hand is no more broken than any of the other 32-bit ABIs, because it does not use 64-bit __kernel_long_t in its n32 ABI.
I have heard from a MIPS porter that one of the flavours suffers from similar problems as x32, just not to that extent. But I don’t recall my source…
MIPS n32 has a lot of the same issues as x86 x32, but I'm pretty sure that the time_t one is not among them.
ioctls. My plan at this point is to eliminate all uses of time_t in the kernel and replace them with time64_t or other safe types. This way, we will eventually find all code that passes 32-bit time types to user space and can fix it. This will take care of the time_t related problems on x32 as well.
Ah, interesting approach. And existing userspace, as well as new userspace that does not declare 64-bit time_t readiness, is still safe on currently-not-broken architectures? So, there’s enough time to fix this before the various libcs turn that on (and it had better be fixed by then, because it becomes ABI by then). Nice idea.
Correct. Another aspect of the approach I'm taking is that the system-call implementation is shared between the native 64-bit case and the new 32-bit case, while the handling for the existing syscalls on 32-bit architectures is shared with the 32-bit compat code on 64-bit architectures. This means if we introduce a bug in either of them, we will find out very quickly and don't have to wait until people start using 64-bit time_t on 32-bit user land.
I am wondering a bit about the ioctls being hard to find. I have not much experience with kernel programming, and even less with Linux than with MS-DOS and BSD, but should not each driver have a central ioctl entry point, from which it should cast the user space data into a (possibly locally declared) structure?
Yes, that's how it works, but unfortunately we have a few thousand drivers that declare an ioctl function, and I hope to do something better than brute-force search all of them. The other point is that we really need to fix all y2038-related bug in drivers, not just the ones in ioctl. This includes things like file systems storing time in 32-bit units on disk, or drivers trying to measure how much time has elapsed without communicating that value elsewhere, but failing when the time_t number goes negative.
Arnd