Re: Update kernel-features.h files for Linux 5.1

[Stepan Golosunov <stepan@golosunov.pp.ru>]

10.05.2019 в 12:11:22 -0300 Adhemerval Zanella написал:
> On 10/05/2019 12:07, Adhemerval Zanella wrote:
> > On 10/05/2019 07:27, Stepan Golosunov wrote:
> >> 09.05.2019 в 23:00:37 +0000 Joseph Myers написал:
> >>> Linux 5.1 adds missing syscalls to the syscall table for many Linux
> >>> kernel architectures.  This patch updates the kernel-features.h
> >>> headers accordingly.  I believe the statfs64 structure used by alpha
> >>> matches what the new kernel syscalls use, but that should be reviewed
> >>> carefully.
> >>>
> >>> Tested with build-many-glibcs.py.
> >>
> >> The newly added direct ipc syscalls are different from the old ones:
> >>
> >> 1. They do not accept IPC_64.  This means that __IPC_64 should be set
> >> to zero when new syscalls are used.  And new syscalls can not be used
> >> for compat functions like __old_semctl.
> > 
> > So it seems we will need to conditionally set __IPC_64 based on kernel
> > version. It also seems that our default value on generic ipc_priv.h
> > is not really expressing the kernel ABI.
> > 
> >>
> >> (Hmm.  Is __old_msgctl already buggy due to its use of __IPC_64 when
> >> __ASSUME_DIRECT_SYSVIPC_SYSCALLS is defined?  Is there any
> >> architecture with both __ASSUME_DIRECT_SYSVIPC_SYSCALLS and
> >> __old_msgctl currently?)
> > 
> > The architectures that exports msgctl@GLIBC_2.0 as compat symbol are
> > alpha, i686, m68k, mips-o32, powerpc32, s390-32, and sparc32. And
> > from these one alpha currently is the only architecture that defines
> > __ASSUME_DIRECT_SYSVIPC_SYSCALLS. So it is buggy for alpha currently
> > and it would be for the aforementioned architectures once they
> > start to use wire-up syscall.
> > 
> > 
> >>
> >> 2. semtimedop does not exist on 32-bit ABIs.  They have
> >> semtimedop_time64 instead.
> >> (I also think that ipc with IPCOP_semtimedop was accidentally made to
> >> behave like semtimedop_time64 in 32-bit builds of linux 5.1.  But that
> >> would be a kernel bug.)
> > 
> > So it seems we would need to either add an __ASSUME specific for semtimedop
> > to just enable wire-up calls if time64 is defined or add another pre-processor
> > check to see if __NR_semtimeop is defined as well.
> > 
> > 
> > To summarize, I think we need too:
> > 
> > 1. Fix Linux msgctl compat function to remove __IPC64.
> > 
> > 2. Move __IPC64 to kernel-feature.h and define it based on kernel version
> >    along with __ASSUME_DIRECT_SYSVIPC_SYSCALLS.
> > 
> > 3. Only use wire-up semtimeop iff __NR_semtimedop is also defined.
> > 
> 
> It seems semop would also need be handled this way.

5. Ensure __old_msgctl, __old_semctl and __old_shmctl do not use
direct syscalls when __IPC64 is zero.