[PATCH 24/25] arm64:ilp32: add vdso-ilp32 and use for signal return

Arnd Bergmann
2016-05-03T09:05:02Z

On Tuesday 03 May 2016 10:00:45 Catalin Marinas wrote:
> On Fri, Apr 29, 2016 at 07:30:19PM +0200, Arnd Bergmann wrote:
> > On Friday 29 April 2016 17:01:55 Catalin Marinas wrote:
> > > On Wed, Apr 06, 2016 at 01:08:46AM +0300, Yury Norov wrote:
> > > > ILP32 VDSO exports next symbols:
> > > > __kernel_rt_sigreturn;
> > > > __kernel_gettimeofday;
> > > > __kernel_clock_gettime;
> > > > __kernel_clock_getres;
> > >
> > > [...]
> > >
> > > > +$(obj)/gettimeofday-ilp32.o: $(src)/../vdso/gettimeofday.S
> > > > + $(call if_changed_dep,vdso-ilp32as)
> > >
> > > Are struct timeval and timespec the same between ILP32 and LP64? For
> > > example, __kernel_gettimeofday() assumes TVAL_TV_SEC offset defined in
> > > asm-offsets.c based on the LP64 timeval.
> >
> > No, ilp32 uses the generic 32-bit data structures, which have a 32-bit
> > time_t. I guess that means it can work for little-endian but not
> > big-endian, right?
>
> I don't think it works for little-endian either. The LP64 struct timeval
> is 16 bytes while the ILP32 one is 8 bytes. The VDSO gettimeofday is
> storing 16 bytes (stp x10, x11, [x0, #TVAL_TV_SEC])

You are right. Yury asked pointed out the same thing on IRC as well.
Using the 64-bit gettimeofday() will put the right number in the
.tv_sec member on little-endian, but will write zeroes to tv_nsec
and corrupt the memory following it.

Yury also tried it out and noticed that for a (so far) unknown reason,
the vdso gets never used by his glibc build, so it has not triggered
any test case failures.

Arnd