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

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

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.