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Re: [PATCH] aarch64: Fix ipc_perm definition for ILP32


On Wed, Aug 23, 2017 at 10:55:02AM +0100, Szabolcs Nagy wrote:
> On 22/08/17 18:46, Steve Ellcey wrote:
> > Here is another aarch64 ILP32 patch.  The mode field in ipc_perm in ILP32
> > should be a 16 bit field, not a 32 bit one.  This was out-of-sync with what the
> > kernel had.  This was causing sysvipc/test-sysvsem to fail in ILP32 mode.
> > This change is only needed for ILP32 so it doesn't need to go in until we add
> > that ABI but I am sending out for review and comments.
> > 
> > 2017-08-22  Yury Norov  <ynorov@caviumnetworks.com>
> > 	    Steve Ellcey  <sellcey@cavium.com>
> > 
> > 	* sysdeps/unix/sysv/linux/aarch64/bits/ipc.h (ipc_perm):
> > 	Ifdef and pad the mode field for ILP32.
> > 
> > 
> > diff --git a/sysdeps/unix/sysv/linux/aarch64/bits/ipc.h b/sysdeps/unix/sysv/linu
> > x/aarch64/bits/ipc.h
> > index cd1f06e..cd05b74 100644
> > --- a/sysdeps/unix/sysv/linux/aarch64/bits/ipc.h
> > +++ b/sysdeps/unix/sysv/linux/aarch64/bits/ipc.h
> > @@ -46,7 +46,12 @@ struct ipc_perm
> >      __gid_t gid;			/* Owner's group ID.  */
> >      __uid_t cuid;			/* Creator's user ID.  */
> >      __gid_t cgid;			/* Creator's group ID.  */
> > +#ifdef __LP64
> >      unsigned int mode;			/* Read/write permission.  */
> > +#else
> > +    unsigned short int mode;		/* Read/write permission.  */
> > +    unsigned short int __pad0;
> > +#endif
> 
> when did this happen?
> 
> as far as i can tell staging/ilp32-4.12 branch in
> git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
> still has unsigned int __kernel_mode_t in uapi, so this is
> an abi change compared to that branch.
> 
> i guess it's for 32bit compat, but i'd like to see the
> kernel patch for this.

It is there from the very beginning of ILP32 patches. The patch changes
the ABI only for arm64/ilp32. LP64 remains untouched, and it works correct
with and without ilp32 patches and this fix.

To reproduce:
struct semid_ds seminfo;
static char name[] = "Hello";

key_t key = ftok (name, 'G');
semid = semget(key, 1, IPC_CREAT | IPC_EXCL | 0644);
semctl (semid, 0, IPC_STAT, &seminfo);
printf("%o\n", seminfo.sem_perm.mode); // bits 16-31 contain garbage

On kernel side no fixes needed because arm64/ilp32 ipc requests are
wired to compat layer, and the layout for structure is like this:
arch/arm64/include/asm/compat.h:
246 struct compat_ipc64_perm {
247         compat_key_t key;
248         __compat_uid32_t uid;
249         __compat_gid32_t gid;
250         __compat_uid32_t cuid;
251         __compat_gid32_t cgid;
252         unsigned short mode;
253         unsigned short __pad1;
254         unsigned short seq;
255         unsigned short __pad2;
256         compat_ulong_t unused1;
257         compat_ulong_t unused2;
258 };

So I would prefer to treat it not as the change of ABI, bit the
fix of ABI incompatibility on GLIBC side.

Yury


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