From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/7752 Path: news.gmane.org!not-for-mail From: Jens Gustedt Newsgroups: gmane.linux.lib.musl.general Subject: Re: ppc soft-float regression Date: Mon, 25 May 2015 08:31:29 +0200 Message-ID: <1432535489.2715.1.camel@inria.fr> References: <20150517163723.GP17573@brightrain.aerifal.cx> <20150517175021.GA2171@euler> <20150517181556.GA23050@euler> <20150517195622.GA4761@euler> <20150518183929.GA6370@euler> <20150518201043.GX17573@brightrain.aerifal.cx> <20150518201422.GY17573@brightrain.aerifal.cx> <20150518220731.GA31132@euler> <20150522062346.GK17573@brightrain.aerifal.cx> <20150524030809.GA19134@brightrain.aerifal.cx> <20150525003648.GO17573@brightrain.aerifal.cx> 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="=-vw9cHVWBasKaUU+IVwXD" X-Trace: ger.gmane.org 1432535511 8154 80.91.229.3 (25 May 2015 06:31:51 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 25 May 2015 06:31:51 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-7764-gllmg-musl=m.gmane.org@lists.openwall.com Mon May 25 08:31:47 2015 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1YwlvL-0000nc-TT for gllmg-musl@m.gmane.org; Mon, 25 May 2015 08:31:44 +0200 Original-Received: (qmail 23625 invoked by uid 550); 25 May 2015 06:31:41 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: Original-Received: (qmail 23606 invoked from network); 25 May 2015 06:31:40 -0000 X-IronPort-AV: E=Sophos;i="5.13,489,1427752800"; d="scan'";a="153700233" In-Reply-To: <20150525003648.GO17573@brightrain.aerifal.cx> Face: 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Cj15cu23XZI4/826Px/xqB37z547sPH374oOvnKTsOb+1zuCoImZARM8ZiLlKkXcWOcoFRJ+Do/CwFO4e2DEe+9Ti+ZXA8ny/cU+X4bMKRZxZIVEiqXI6/+NKuUzPHb7z40ovnX3zx+Ctuq38HyuqWG7Tu+A0AAAAASUVORK5CYII= X-Mailer: Evolution 3.12.9-1+b1 Xref: news.gmane.org gmane.linux.lib.musl.general:7752 Archived-At: --=-vw9cHVWBasKaUU+IVwXD Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Am Sonntag, den 24.05.2015, 20:36 -0400 schrieb Rich Felker: > There's a simple alternative I just came up with though: have > dlstart.c compute the number of REL entries that need their addends > saved and allocate a VLA on its stack for stages 2 and 3 to use. While > the number of addends could be significant, it's many orders of > magnitude smaller than the smallest practical stack sizes we could > actually run with, so it's perfectly safe to put it on the stack. >=20 > Here're the basic changes I'd like to make to dlstart.c to implement > this: >=20 > 1. Remove processing of DT_JMPREL REL/RELA table. All entries in this > table are necessarily JMP_SLOT type, and thus symbolic, so there's > nothing stage 1 can do with them anyway. Also, being JMP_SLOT type, > they have implicit addends of zero if they're REL-type, so there's > no need to save addends. >=20 > 2. Remove the loop in dlstart.c that works like a fake function call 3 > times to process DT_JMPREL, DT_REL, and DT_RELA. Instead we just > need 2 iterations, and now the stride is constant in each, so they > should simplify down a lot more inline. >=20 > 3. During the loop that processes DT_REL, count the number of > non-relative relocations (ones we skip at this stage), then make a > VLA this size and pass its address to __dls2 as a second argument. >=20 > 4. Have the do_relocs in stage 2 save addends in this provided array > before overwriting them, and save its address for use by stage 3. >=20 > 5. Have the do_relocs in stage 3 (for ldso/libc only) pull addends > from this array instead of of from inline. >=20 > Steps 1 and 2 are purely code removal/simplification and should be > done regardless of whether we move forward on the above program, I > think. Steps 3-5 add some complexity but hardly any code, just a few > lines here and there. >=20 > Comments? I like it. The thing that is a bit critical here, is the VLA. Not because it is a VLA as such, but because it is a dynamic allocation on the stack. We already have a similar strategy in pthread_create for TLS. The difference is that there we have - a sanity check - an alternative strategy if the sanity check fails Would there be a possibility to have both here, too? Thanks Jens --=20 :: INRIA Nancy Grand Est ::: Camus ::::::: ICube/ICPS ::: :: ::::::::::::::: office Strasbourg : +33 368854536 :: :: :::::::::::::::::::::: gsm France : +33 651400183 :: :: ::::::::::::::: gsm international : +49 15737185122 :: :: http://icube-icps.unistra.fr/index.php/Jens_Gustedt :: --=-vw9cHVWBasKaUU+IVwXD 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 v2 iEYEABECAAYFAlViwcEACgkQD9PoadrVN+KQnACfYwVL/RL3F53PgIuGi7GuGeKb 7U8An2lP/IxEx11Ca1ZXBtcoczUyjIUk =TUX2 -----END PGP SIGNATURE----- --=-vw9cHVWBasKaUU+IVwXD--