Re: [PATCH v2] Test errno setup

[Yury Norov <ynorov at caviumnetworks dot com>]

On Thu, Mar 09, 2017 at 05:30:03PM +0100, Adhemerval Zanella wrote:
> > Regarding mlock-syscall:
> > If the compat mlock syscall is used, it returns 12 (ENOMEM).
> > This is also observable if you compile and run the testcase with -m32 on a x86_64 system.
> > 
> > 
> > I've compiled and run posix/test-errno.c on my s390x system and
> > get the following error:
> > FAIL: setsockopt: errno is: 22 (Invalid argument) expected: 9 (Bad file descriptor)
> > 
> > sl=0xfdfa9170 before setsockopt syscall.
> > The test succeeds if I sl is initialized to zero.
> > 
> 
> POSIX [1] states that mlock should may fail with EINVAL only if
> the addr argument is not a multiple of {PAGESIZE}.  Linux does
> not return this issue, since it aligns the resulting address
> to pagesize:
> 
> * mm/mlock.c:
> 
> 666 static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t flags)
> 667 {
> [...]
> 676 
> 677         len = PAGE_ALIGN(len + (offset_in_page(start)));
> 678         start &= PAGE_MASK;
> 
> EINVAL is only returned on 'apply_vma_lock_flags':
> 
> 578 static int apply_vma_lock_flags(unsigned long start, size_t len,
> 579                                 vm_flags_t flags)
> 580 {
> [...]
> 587         end = start + len;
> 588         if (end < start)
> 589                 return -EINVAL;
> 
> But if you runs 32 binaries on 64 bits kernel overflow won't happen.
> It is documented in man pages, so I think from kernel side it should
> be consistent for 32 bit binaries on 64 bit kernel.

I also observed this fail in aarch64/ilp32, but I decided that this
is the ilp32 problem while it's compat one, as you discovered here.

The test is not intended to check each and every syscall, as it is
mentioned in comment. For example, all syscalls that may fail with
EFAULT are not tested because they may both return the EFAULT or
actually terminate the application with segfault. This is the
similar case for me. I think that it's better to keep the test simple,
and just drop the mlock test, and not introduce another macro.

Though, the patch that handles the issue is already there, and I don't
object if you submit it.

Yury