Re: [PATCH] y2038: Remove newstat family from default syscall set

[Guenter Roeck]

On 09/06/2018 02:45 AM, Palmer Dabbelt wrote:
> On Sat, 01 Sep 2018 10:43:53 PDT (-0700), linux@xxxxxxxxxxxx wrote:
> > Hi Arnd,
> >
> > On Fri, Apr 13, 2018 at 11:50:12AM +0200, Arnd Bergmann wrote:
> > > We have four generations of stat() syscalls:
> > > - the oldstat syscalls that are only used on the older architectures
> > > - the newstat family that is used on all 64-bit architectures but
> > > Â lacked support for large files on 32-bit architectures.
> > > - the stat64 family that is used mostly on 32-bit architectures to
> > > Â replace newstat
> > > - statx() to replace all of the above, adding 64-bit timestamps among
> > > Â other things.
> > >
> > > We already compile stat64 only on those architectures that need it,
> > > but newstat is always built, including on those that don't reference
> > > it. This adds a new __ARCH_WANT_NEW_STAT symbol along the lines of
> > > __ARCH_WANT_OLD_STAT and __ARCH_WANT_STAT64 to control compilation of
> > > newstat. All architectures that need it use an explict define, the
> > > others now get a little bit smaller, and future architecture (including
> > > 64-bit targets) won't ever see it.
> >
> > This patch causes my riscv boot tests to crash in -next
>
> Ah, thanks for running these!
>
> > sbin/init: error while loading shared libraries: libc.so.6: cannot stat shared object: Error 38
> > Kernel panic - not syncing: Attempted to kill init! exitcode=0x00007f00
> >
> > The following change fixes the problem for me, but of course I have no idea
> > if it is correct. Copying RISC-V maintainers for input.
> >
> > Guenter
> >
> > ---
> > diff --git a/arch/riscv/include/asm/unistd.h b/arch/riscv/include/asm/unistd.h
> > index 0caea01d5cca..eff7aa9aa163 100644
> > --- a/arch/riscv/include/asm/unistd.h
> > +++ b/arch/riscv/include/asm/unistd.h
> > @@ -16,6 +16,7 @@
> >  * be included multiple times. See uapi/asm/syscalls.h for more info.
> > Â */
> >
> > +#define __ARCH_WANT_NEW_STAT
> > Â#define __ARCH_WANT_SYS_CLONE
> > Â#include <uapi/asm/unistd.h>
> > Â#include <uapi/asm/syscalls.h>
>
> I'm afraid I'm not sure what the right thing to do here is either, but from the patch description it does seem like we should have this guarded by an "#ifdef CONFIG_32BIT" so we can keep it out of our 32-bit ABI (which isn't in glibc yet, so isn't stable) in favor of statx() (or maybe stat64()?). The one problem here is that I can't find "newstat" anywhere in glibc to verify it's actually supposed to be part of our 64-bit ABI, though I can find a bunch of references to "statx" that seem to indicate it's meant to be present.
>
> That said, assuming you don't have anything wacky going on in userspace if this breaks the ABI then it breaks the ABI, so however newstat got into a binary we still need to keep it around. Poking around my Fedora glibc image I see

userspace is a root file system built with buildroot (modified to support riscv64),
using glibc 2.26. Nothing wacky, sorry.

Guenter