Re: [RFC v3 23/23] RISC-V: Use 64-bit vdso syscalls

[Alistair Francis <alistair23 at gmail dot com>]

On Wed, Jul 17, 2019 at 4:42 PM Alistair Francis <alistair23@gmail.com> wrote:
>
>  On Wed, Jul 17, 2019 at 3:23 PM Alistair Francis <alistair23@gmail.com> wrote:
> >
> > On Wed, Jul 17, 2019 at 1:02 AM Arnd Bergmann <arnd@arndb.de> wrote:
> > >
> > > On Wed, Jul 17, 2019 at 7:33 AM Florian Weimer <fweimer@redhat.com> wrote:
> > > >
> > > > * Alistair Francis:
> > > >
> > > > > Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
> > > > > ---
> > > > >  sysdeps/unix/sysv/linux/riscv/init-first.c | 4 ++--
> > > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/sysdeps/unix/sysv/linux/riscv/init-first.c b/sysdeps/unix/sysv/linux/riscv/init-first.c
> > > > > index 155a4a2c0c..fa9c690cdd 100644
> > > > > --- a/sysdeps/unix/sysv/linux/riscv/init-first.c
> > > > > +++ b/sysdeps/unix/sysv/linux/riscv/init-first.c
> > > > > @@ -43,11 +43,11 @@ _libc_vdso_platform_setup (void)
> > > > >    PTR_MANGLE (p);
> > > > >    VDSO_SYMBOL (gettimeofday) = p;
> > > > >
> > > > > -  p = _dl_vdso_vsym ("__vdso_clock_gettime", &linux_version);
> > > > > +  p = _dl_vdso_vsym ("__vdso_clock_gettime64", &linux_version);
> > > > >    PTR_MANGLE (p);
> > > > >    VDSO_SYMBOL (clock_gettime) = p;
> > > > >
> > > > > -  p = _dl_vdso_vsym ("__vdso_clock_getres", &linux_version);
> > > > > +  p = _dl_vdso_vsym ("__vdso_clock_getres_time64", &linux_version);
> > > > >    PTR_MANGLE (p);
> > > > >    VDSO_SYMBOL (clock_getres) = p;
> > > > >  }
> > > >
> > > > I believe this will lose vDSO acceleration for RV64 on older kernels
> > > > which do not define __vdso_clock_getres_time64.
> > >
> > > Also newer kernels, as 64-bit kernels only have __vdso_clock_getres,
> > > not __vdso_clock_getres_time64.
>
> Just to confirm (based on this thread and "RISC-V: Use 64-bit timespec
> in clock_gettime vdso calls"):
>  - change the clock_gettime64 vdso symbol to  __clock_gettime64 for
> RV32 to match the kernel

Wait this breaks all of the callers of INTERNAL_VSYSCALL() as the
syscall is just __NR_clock_gettime64 not __NR___clock_gettime64.

Alistair

>  - Remove clock_gettime, clock_getres and gettimeofday vdso calls for RV32
>
> Alistair
>
> >
> > Ok, I can #ifdef this based on word size.
> >
> > Alistair
> >
> > >
> > >        Arnd