Re: Use of size_t and ssize_t in mseek

[Jens Gustedt <jens.gustedt@inria.fr>]

[-- Attachment #1: Type: text/plain, Size: 3845 bytes --]

Am Donnerstag, den 04.07.2013, 02:37 -0400 schrieb Rich Felker:
> > unless one would finally implement them separately, of course
> 
> Yes but that's a huge maintenance burden (duplicate functionality) and
> while it's less bloat for individual static apps that don't use Annex
> K, it's much more bloat for libc.a and libc.so.

sure, I mentioned this merely for completeness, I don't think that
this is a viable option

> No, I mean just the sheer volume of interfaces to add.

The number of interfaces wouldn't scare me too much, and it would be
relatively easy to start supporting that incrementally.

> qsort_s can store the comparison function and context in TLS, and then
> pass to qsort a comparison function that grabs these from TLS and
> calls the original comparison function with the context pointer. This
> is valid assuming qsort does not run the comparisons in new threads.

sure, but for an execution of qsort_s this would have a lot of
indirections and a call to TLS for every comparison. For performance
sensible functions like this, this doesn't sound very attractive.

(In P99 I do that with inlining and gcc shows to be able to expand all
comparisons in place and to optimize that smoothly.)

> TLS is not guaranteed to exist when these functions are called;
> programs not using any multi-threaded functionality are supposed to
> "basically work" on Linux 2.4. I don't mind having the Annex K
> functions depend on TLS, since only new programs will use them anyway,
> but I don't want to break existing programs.

My guess would be that you can alias the TLS variable that would
control that behavior to a simple global variable in the case of
absence of threads.

> What I was saying is that, in library code, you can't rely on this.
> The application may have installed a handler that causes the functions
> to just return an error, or the default implementation-defined handler
> might do so.

sure, but I don't see any problem in this. continuing execution is
one of the permitted path that a constraint handler may take. these
are user interfaces, not meant to be used internally by the C library,
I think.

> > > My feeling is that we should hold off on a decision about them to
> > > see if any applications actually start using them.
> > 
> > I think we have a hen and egg problem, here. Nobody will use them if
> > nobody provides an implementation.
> 
> You presume we would want people to use them. :) I don't. I think
> they're very poorly designed interfaces that were crammed into the
> standards process by their sponsor's clout rather than any technical
> merit of existing practice.

AFAIK they had some existing practice in the MS world

I think there are some of these interfaces that are not too bad, from
a user perspective these interfaces are relatively simple to use.

Especially qsort_s is nice and I also see advantages in being able to
inhibit certain dangerous printf or scanf formats.

> _FORTIFY_SOURCE solves pretty much the same problems these functions
> were intended to solve, but does a much better job since it doesn't
> rely on the application developer to provide truthful information
> about object sizes, and instead gets the compiler to do it.

In C, applications *have* to have a consistent view of the size of
their buffers. So I don't see much of a burden, here. I started to use
them (through my P99 implementation) and I didn't find anything
remarkably heavy.

Jens

-- 
:: INRIA Nancy Grand Est :: http://www.loria.fr/~gustedt/   ::
:: AlGorille ::::::::::::::: office Nancy : +33 383593090   ::
:: ICube :::::::::::::: office Strasbourg : +33 368854536   ::
:: ::::::::::::::::::::::::::: gsm France : +33 651400183   ::
:: :::::::::::::::::::: gsm international : +49 15737185122 ::




[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 198 bytes --]