Re: [PATCH 4/5] s390: autogenerate compat syscall wrappers

[Heiko Carstens]

On Wed, Jan 16, 2019 at 02:15:22PM +0100, Arnd Bergmann wrote:
> Any system call that takes a pointer argument on s390 requires
> a wrapper function to do a 31-to-64 zero-extension, these are
> currently generated in arch/s390/kernel/compat_wrapper.c.
> 
> On arm64 and x86, we already generate similar wrappers for all
> system calls in the place of their definition, just for a different
> purpose (they load the arguments from pt_regs).
> 
> We can do the same thing here, by adding an asm/syscall_wrapper.h
> file with a copy of all the relevant macros to override the generic
> version. Besides the addition of the compat entry point, these also
> rename the entry points with a __s390_ or __s390x_ prefix, similar
> to what we do on arm64 and x86. This in turn requires renaming
> a few things, and adding a proper ni_syscall() entry point.
> 
> In order to still compile system call definitions that pass an
> loff_t argument, the __SC_COMPAT_CAST() macro checks for that
> and forces an -ENOSYS error, which was the best I could come up
> with. Those functions must obviously not get called from user
> space, but instead require hand-written compat_sys_*() handlers,
> which fortunately already exist.
> 
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  arch/s390/Kconfig                       |   1 +
>  arch/s390/include/asm/syscall_wrapper.h | 136 ++++++++++++++++++++++++
>  arch/s390/kernel/compat_wrapper.c       |  23 +---
>  arch/s390/kernel/entry.S                |   4 +-
>  arch/s390/kernel/sys_s390.c             |   5 +
>  5 files changed, 148 insertions(+), 21 deletions(-)
>  create mode 100644 arch/s390/include/asm/syscall_wrapper.h

This broke system call tracing. We also need the patch below. If there
aren't any objections this should be added to Martin's 'compat' branch.