[PATCH 03/15] sparc: Use Linux kABI for syscall return

[Florian Weimer]

* Adhemerval Zanella:

>> But ERESTART_RESTARTBLOCK is not 4095, so glibc with this change will
>> now treat certain internal kernel error codes as errors, while they
>> were previously reported as success.  This looks like a kernel bug, in
>> that ERESTART_RESTARTBLOCK was not updated when more error codes were
>> added.  On the other hand, these error codes should never leak into
>> userspace.
>
> My understanding is such errors should not be visible by the application,
> as indicated by include/linux/errno.h comment. And it seems to be the
> case for sparc, at least on:

These error codes tend to leak from device drivers and other less
scrutinized parts of the kernel.  It's not actually about the
ERESTART_RESTARTBLOCK value as such, there are other values larger
than that:

#define ERESTART_RESTARTBLOCK 516 /* restart by calling sys_restart_syscall */
#define EPROBE_DEFER    517     /* Driver requests probe retry */
#define EOPENSTALE      518     /* open found a stale dentry */
#define ENOPARAM        519     /* Parameter not supported */

/* Defined for the NFSv3 protocol */
#define EBADHANDLE      521     /* Illegal NFS file handle */
#define ENOTSYNC        522     /* Update synchronization mismatch */
#define EBADCOOKIE      523     /* Cookie is stale */
#define ENOTSUPP        524     /* Operation is not supported */

And so on.

Like I said, it looks like someone forgot to update this code.  It
probably should use the 4095 boundary and not specific error codes
anyway.  (We had a similar problem in glibc itself in the s390
socketcall support.)