public inbox for gcc-cvs-wwwdocs@sourceware.org help / color / mirror / Atom feed
From: Jonathan Wakely <redi@sourceware.org> To: gcc-cvs-wwwdocs@gcc.gnu.org Subject: gcc-wwwdocs branch master updated. f1d2be6c9fcc52d676266e7ede123953d150aaf3 Date: Thu, 7 May 2020 10:24:56 +0000 (GMT) [thread overview] Message-ID: <20200507102456.617A0395A40E@sourceware.org> (raw) [-- Warning: decoded text below may be mangled, UTF-8 assumed --] [-- Attachment #1: Type: text/plain, Size: 3861 bytes --] This is an automated email from the git hooks/post-receive script. It was generated because a ref change was pushed to the repository containing the project "gcc-wwwdocs". The branch, master has been updated via f1d2be6c9fcc52d676266e7ede123953d150aaf3 (commit) from 01424bc265a033851b93d0ce0e84df3ce519f429 (commit) Those revisions listed above that are new to this repository have not appeared on any other notification email; so we list those revisions in full, below. - Log ----------------------------------------------------------------- commit f1d2be6c9fcc52d676266e7ede123953d150aaf3 Author: Jonathan Wakely <jwakely@redhat.com> Date: Thu May 7 11:24:04 2020 +0100 Document C++17 ABI changes in GCC 10 diff --git a/htdocs/gcc-10/changes.html b/htdocs/gcc-10/changes.html index f5b70eb4..52fd6e6a 100644 --- a/htdocs/gcc-10/changes.html +++ b/htdocs/gcc-10/changes.html @@ -30,6 +30,12 @@ a work-in-progress.</p> <!-- .................................................................. --> <h2>Caveats</h2> <ul> + <li> + An ABI incompatibility between C++14 and C++17 has been fixed. On some + targets a class with a zero-sized subobject would be passed incorrectly + when compiled as C++17 or C++20. + See the <a href="#empty_base">C++ notes below</a> for more details. + </li> <li> The deprecated Profile Mode and <code>array_allocator</code> extensions have been removed from libstdc++. @@ -409,6 +415,39 @@ int get_naïve_pi() { The attribute <code>deprecated</code> can now be used on <code>namespace</code>s too. </li> + <li> + <a name="empty_base">The ABI</a> + of passing and returning certain C++ classes by value changed + on several targets in GCC 10, including + <a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94383">AArch64</a>, + <a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94711">ARM</a>, + <a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94383">PowerPC ELFv2</a>, + <a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94704">S/390</a> + and + <a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94706">Itanium</a>. + These changes affect classes with a zero-sized + subobject (an empty base class, or data member with the + <code>[[no_unique_address]]</code> attribute) where all other non-static + data members have the same type (this is called a "homogeneous aggregate" + in some ABI specifications, or if there is only one such member, + a "single element"). + In <code>-std=c++17</code> and <code>-std=c++20</code> modes, classes with + an empty base class were not considered to have a single element or + to be a homogeneous aggregate, and so could be passed differently + (in the wrong registers or at the wrong stack address). This could make + code compiled with <code>-std=c++17</code> and <code>-std=c++14</code> + ABI incompatible. This has been corrected and the empty bases are + ignored in those ABI decisions, so functions compiled with + <code>-std=c++14</code> and <code>-std=c++17</code> are now ABI compatible + again. + Example: + <code>struct empty {}; struct S : empty { float f; }; void f(S);</code>. + Similarly, in classes containing non-static data members with empty + class types using the C++20 <code>[[no_unique_address]]</code> attribute, + those members weren't ignored in the ABI argument passing decisions + as they should be. Both of these ABI changes are now diagnosed with + <code>-Wpsabi</code>. + </li> </ul> <h4 id="libstdcxx">Runtime Library (libstdc++)</h4> ----------------------------------------------------------------------- Summary of changes: htdocs/gcc-10/changes.html | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) hooks/post-receive -- gcc-wwwdocs
reply other threads:[~2020-05-07 10:24 UTC|newest] Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
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=20200507102456.617A0395A40E@sourceware.org \ --to=redi@sourceware.org \ --cc=gcc-cvs-wwwdocs@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).