Re: [RESEND][PATCH v2 1/3] syscalls,x86 Expose arch_prctl on x86-32.

[Kyle Huey]

On Wed, Sep 14, 2016 at 2:59 PM, Dmitry Safonov <0x7f454c46@xxxxxxxxx> wrote:
> 2016-09-15 0:08 GMT+03:00 Kyle Huey <me@xxxxxxxxxxxx>:
>> Signed-off-by: Kyle Huey <khuey@xxxxxxxxxxxx>
>> ---
>>  arch/x86/entry/syscalls/syscall_32.tbl |  1 +
>>  arch/x86/kernel/process.c              | 80 ++++++++++++++++++++++++++++++++++
>>  arch/x86/kernel/process_64.c           | 66 ----------------------------
>>  3 files changed, 81 insertions(+), 66 deletions(-)
>>
>> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
>> index f848572..3b6965b 100644
>> --- a/arch/x86/entry/syscalls/syscall_32.tbl
>> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
>> @@ -386,3 +386,4 @@
>>  377    i386    copy_file_range         sys_copy_file_range
>>  378    i386    preadv2                 sys_preadv2                     compat_sys_preadv2
>>  379    i386    pwritev2                sys_pwritev2                    compat_sys_pwritev2
>> +380    i386    arch_prctl              sys_arch_prctl
>
> Why not define it as other 32-bit syscalls with compat_sys_ prefix
> with the help of COMPAT_SYSCALL_DEFINE() macro?
> Then you could omit code moving, drop is_32 helper.
> I miss something obvious?

The code will have to move regardless, because right now do_arch_prctl
is in process-64.c which is only compiled on a 64 bit kernel.

As I told Dave Hansen in the non-RESEND thread (not sure why
git-send-email didn't put him in this one ...) I considered doing a
compat_sys_arch_prctl that would reject the relevant arch_prctls that
don't apply on 32 bit but I didn't see any prior art for it (in my
admittedly non-exhaustive search).

- Kyle