Re: 32-bit time_t inside itimerval

[Lukasz Majewski <lukma@denx.de>]

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Hi Arnd, Alistair,

Sorry to jump in lately - Christmas period :-)

> On Mon, Dec 30, 2019 at 10:22 PM Alistair Francis
> <alistair23@gmail.com> wrote:
> > On Mon, Dec 30, 2019 at 12:11 PM Arnd Bergmann <arnd@arndb.de>
> > wrote:  
> > > On Mon, Dec 30, 2019 at 8:57 PM Alistair Francis
> > > <alistair23@gmail.com> wrote:  
> > > >
> > > > Yeah, agreed. I have updated the RV32 port to internally convert
> > > > between 32/64-bit.  
> > >
> > > Any chance of making this the default implementation for 32-bit
> > > rather than RV32 specific? The code should be the same for any
> > > time64 user space regardless of the architecture.  
> >
> > I was thinking about this.
> >
> > I don't know of a good way to make it apply only to 32-bit archs
> > with a 64-bit time_t.This could actually just apply to all 32-bit
> > archs. That way ones that are 64-bit time_t are covered and ones
> > that aren't will just do an extra conversion with no effect.
> >
> > Making it 32-bit in general seems reasonable to me, I just have to
> > figure out a way to test it though.  
> 
> Maybe Lukasz already has a plan for this,

I did not do any work regarding {set|get}itimer. I've instead focused on
timer_fd[sg]ettime for now [1].

> I don't think it's
> fundamentally different from the other system calls that he has
> converted already to work with time64 callers.

I'm not aware of any RV32 specifics, but it seems to me that it would
be appropriate to use the 64 bit version of struct __itimerspec64 in
glibc - as for example in the conversion patch from [1].

As it was already mentioned - those calls set the time to be
decremented and do not operate on "absolute" time values.
Hence, I think that it would be good enough (for now?) to use 32 bit
API wrapped into 64 bit internal glibc values and just return errors
when somebody wants to set timer relative expiration time to overflow
time_t on 32 bit archs (arm,rv32).

(The above approach would also simplify latter glibc switch to *_time64
syscalls when introduced).

> 
>       Arnd

Arnd, am I correct that the struct itimerval to __kernel_old_itimerval
conversion patch can be found here [2]? 


Links:

[1] - https://patchwork.ozlabs.org/patch/1211482/
[2] -
https://git.kernel.org/pub/scm/linux/kernel/git/arnd/playground.git/commit/?h=y2038&id=4f9fbd893fe83a1193adceca41c8f7aa6c7382a1


Best regards,

Lukasz Majewski

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