public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "whaley at cs dot utsa dot edu" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/38496] Gcc misaligns arrays when stack is forced follow the x8632 ABI Date: Thu, 11 Dec 2008 23:26:00 -0000 [thread overview] Message-ID: <20081211232511.27129.qmail@sourceware.org> (raw) In-Reply-To: <bug-38496-12761@http.gcc.gnu.org/bugzilla/> ------- Comment #4 from whaley at cs dot utsa dot edu 2008-12-11 23:25 ------- >aligning the stack to 16 bytes is complaint It might be complaint, but it certainly isn't compliant. The ABI says that you can assume 4-byte alignment, and not all 4-byte alignments are 16-byte aligned (obviously). Therefore, by assuming 16-byte alignment, gcc is not compliant with the ABI. The whole point of an ABI is so that code knows how to call each other. The place I know this happens is Windows, which follows the ABI and aligns the stack to 4-byte boundaries. Therefore, when a windows-compiled library attempts to call a gcc-compiled routine, the gcc-compiled routine seg faults/bus errors because it assumes an alignment that is not specified by the ABI. >> generates double precision arrays that are not aligned to 8-byte boundaries >That is ok. There is no interoperability here really. The problem for interoperability is that every sane compiler forces all array boundaries to a multiple of the underlying type, to avoid cache line splits, which essentially double the cost of a load. I am aware that neither the C nor Fortran standards guarantee native alignment, but every cache-based architecture needs it for good performance and thus most code assumes it. So, aligning to 4-byte boundary is not OK (cache line splits), and it does cause interoperability problems (code expects native alignment for arrays). >Now with -malign-double they will get aligned but you just changed the ABI to have that requirement. No, with -malign-double, they are still not aligned. Wanting to follow the ABI should not preclude native alignment on arrays. Are you saying that when you pass -malign-double with stack-boundary=2, you get 8-byte aligned arrays? Thanks, Clint -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38496
next prev parent reply other threads:[~2008-12-11 23:26 UTC|newest] Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top 2008-12-11 22:54 [Bug fortran/38496] New: " whaley at cs dot utsa dot edu 2008-12-11 23:03 ` [Bug fortran/38496] " whaley at cs dot utsa dot edu 2008-12-11 23:05 ` [Bug target/38496] " pinskia at gcc dot gnu dot org 2008-12-11 23:06 ` pinskia at gcc dot gnu dot org 2008-12-11 23:26 ` whaley at cs dot utsa dot edu [this message] 2008-12-11 23:29 ` pinskia at gcc dot gnu dot org 2008-12-11 23:44 ` whaley at cs dot utsa dot edu 2008-12-12 0:02 ` joseph at codesourcery dot com 2008-12-12 0:53 ` whaley at cs dot utsa dot edu 2008-12-12 1:06 ` hjl dot tools at gmail dot com 2008-12-12 1:26 ` joseph at codesourcery dot com 2008-12-12 1:50 ` whaley at cs dot utsa dot edu 2008-12-15 0:23 ` joseph at codesourcery dot com 2008-12-15 14:54 ` whaley at cs dot utsa dot edu 2008-12-15 18:19 ` joseph at codesourcery dot com 2008-12-15 21:34 ` whaley at cs dot utsa dot edu 2008-12-15 21:39 ` Andrew Thomas Pinski 2008-12-15 21:40 ` pinskia at gmail dot com 2008-12-15 22:03 ` whaley at cs dot utsa dot edu 2008-12-15 23:02 ` Andrew Pinski 2008-12-15 23:03 ` pinskia at gmail dot com 2008-12-15 23:40 ` whaley at cs dot utsa dot edu 2008-12-16 0:10 ` joseph at codesourcery dot com 2009-03-18 13:25 ` sliwa at cft dot edu dot pl 2009-07-23 13:14 ` jakub at gcc dot gnu dot org 2009-07-23 14:35 ` mikulas at artax dot karlin dot mff dot cuni dot cz 2009-07-24 12:16 ` rguenth at gcc dot gnu dot org 2009-07-24 17:05 ` whaley at cs dot utsa dot edu 2009-07-31 1:18 ` mikulas at artax dot karlin dot mff dot cuni dot cz 2009-10-23 9:45 ` rguenth at gcc dot gnu dot org [not found] <bug-38496-4@http.gcc.gnu.org/bugzilla/> 2014-02-16 13:12 ` jackie.rosen at hushmail dot com
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20081211232511.27129.qmail@sourceware.org \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).