From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/4502 Path: news.gmane.org!not-for-mail From: Jens Gustedt Newsgroups: gmane.linux.lib.musl.general Subject: Re: Discussion of partly-invasive changes needed for x32 port Date: Mon, 20 Jan 2014 11:55:39 +0100 Message-ID: <1390215339.6398.371.camel@eris.loria.fr> References: <20140120074131.GA3529@brightrain.aerifal.cx> <52DCE1B8.3020100@gentoo.org> <1390209922.6398.365.camel@eris.loria.fr> <52DCF67A.3020706@barfooze.de> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-iqn8Uzuai1r9t2m4mECq" X-Trace: ger.gmane.org 1390215349 9731 80.91.229.3 (20 Jan 2014 10:55:49 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 20 Jan 2014 10:55:49 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: 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Cj15cu23XZI4/826Px/xqB37z547sPH374oOvnKTsOb+1zuCoImZARM8ZiLlKkXcWOcoFRJ+Do/CwFO4e2DEe+9Ti+ZXA8ny/cU+X4bMKRZxZIVEiqXI6/+NKuUzPHb7z40ovnX3zx+Ctuq38HyuqWG7Tu+A0AAAAASUVORK5CYII= X-Mailer: Evolution 3.2.3-0ubuntu6 Xref: news.gmane.org gmane.linux.lib.musl.general:4502 Archived-At: --=-iqn8Uzuai1r9t2m4mECq Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Am Montag, den 20.01.2014, 11:12 +0100 schrieb John Spencer: > what rich had in mind was usage of _Generic in the x32 __scc=20 > (syscall-cast) macro: >=20 > instead of >=20 > #define __scc(X) sizeof(1?(X):0ULL) < 8 ? (unsigned long) (X) : (long=20 > long) (X) >=20 > something along the lines of > _Generic((X), struct timespec*: &(struct timespec){.sec =3D (X).sec, .nse= c=20 > =3D (X).nsec}, default: sizeof(1?(X):0ULL) < 8 ? (unsigned long) (X) := =20 > (long long) (X)) ah, I see how _Generic could pop in an make some wrappers for architecture specific code nicer In the concrete case I don't understand too well. The return type of that generic expression would be of a fundamentally different type, once a pointer to struct, otherwise an integer. Also the two struct types should be different types, no? One the userland type and the other the kernel type? But then something like &(struct kernel_timespec){.sec =3D (X)->sec, .nsec =3D (X)->nsec} should suffice to capture the transition well. This would certainly benefit of a wrapper function kernel_timespec_copy, because it evaluates X twice : kernel_timespec_copy(&(struct kernel_timespec){0}, (X)) If you want that for optimization reasons you could try to capture if the two types agree and avoid the extra copy. Something along the line of _Generic((X), struct kernel_timespec*: (X), default: kernel_timespec_copy(&(struct kernel_timespec*){0}, (X)) ) But I am not convinced that this can't be just achieved by doing some #ifdef programming > however the only available compiler implementing _Generic is Clang. > not even GCC 4.8.2 supports it. however i've seen some pseudo _Generic= =20 > implementation on your blog [1], imo we could use the bits described=20 > there, namely > " > __typeof__(EXP) gives the type of the expression EXP > __builtin_types_compatible_p(T1, T2) is true if the two types are= =20 > compatible > __builtin_choose_expr(CNTRL, EXP1, EXP2) choose between the two=20 > expressions at compile time. > " >=20 > to implement the above macro, as x32 requires a very recent GCC (>=3D 4.7= )=20 > anyway, i see no big problem in using those gcc helpers in lieu of _Gener= ic. These features are supported since long in gcc and clang, I think, so yes from that side there certainly would be not much of an obstacle. But I wouldn't think that using such a feature just in such an isolated spot (very restricted part of code and very specific architecture) would be worth it. Some cooked down version of _Generic could perhaps be beneficial for the whole of musl, there are some places that implement type genericity in some handcrafted way. But these things need macro magic and should not be re-implemented at each point where they are needed. So probably much too intrusive at this point in time. Jens --=20 :: 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 :: --=-iqn8Uzuai1r9t2m4mECq Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iEYEABECAAYFAlLdAKsACgkQD9PoadrVN+LZFwCfRskAhsGIRmlaYmgOVtKYi1VE zr4An2Gbr9NBBQMLXh42Ac6im/FRBdnt =lQ91 -----END PGP SIGNATURE----- --=-iqn8Uzuai1r9t2m4mECq--