Re: [PATCH 00/10] nptl: Fix Race conditions in pthread cancellation (BZ#12683)

[Joseph Myers <joseph at codesourcery dot com>]

On Fri, 18 Sep 2015, Adhemerval Zanella wrote:

> I see for such cases the port would need to provide extra implementation
> for such symbols in the case (as the fstat for x32 does).  I see this a
> better approach, but I am open to suggestions.

I'm not clear on what you're referring to as "fstat for x32" - I don't see 
an fstat implementation in sysdeps/unix/sysv/linux/x86_64/x32/ - but in 
any case, it's generally desirable to avoid the need for 
architecture-specific implementations of functions if we can do something 
generic instead.  And fstat isn't a good example as its only non-error 
return is 0 (like most syscalls) so the return type doesn't matter.

> And for lseek we need to define for GLIBC if this function is indeed a
> cancellation entrypoint of not and make it consistent for all architectures
> (and POSIX states it an optional one [1]).
> 
> [1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_09_05_02

Yes, we need to make this consistent unless there is a good reason for the 
inconsistency.

It seems lseek was made not-cancellable for some systems by

2003-07-14  Ulrich Drepper  <drepper@redhat.com>

        More cancellation handling fixups.
[...]
        * sysdeps/unix/sysv/linux/llseek.c: Must not be cancelable.
        * sysdeps/unix/syscalls.list: Don't mark lseek as cancelable.

(see <https://sourceware.org/ml/libc-hacker/2003-07/msg00012.html>) but 
that didn't make the change for 64-bit architectures.  (But it's marked 
with __THROW.)

> One way is to make the return syscall another type like __syscall_arg_t
> and make the specific implementation for such ports to redefine it to
> a better one if it is required.

I think that's the right logical thing to do to handle such ABIs more 
cleanly and reliably.

Whether it's needed for this patch series could be determined by examining 
all syscalls.list entries for cancellable syscalls that can be used for 
ILP32 configurations with 64-bit registers used in the syscall interface 
(that's MIPS n32 and x86_64 x32, and I'm not sure about what the syscall 
interface for tilegx32 looks like), to see if any beyond lseek can return 
non-error values 2^32 or more.

-- 
Joseph S. Myers
joseph@codesourcery.com