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From: Jakub Jelinek <jakub@sourceware.org> To: gcc-cvs-wwwdocs@gcc.gnu.org Subject: gcc-wwwdocs branch master updated. 3be1a28f58d6063258407b0751e8fb55df4749c8 Date: Wed, 30 Mar 2022 11:16:31 +0000 (GMT) [thread overview] Message-ID: <20220330111631.B9E973858405@sourceware.org> (raw) 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 3be1a28f58d6063258407b0751e8fb55df4749c8 (commit) from caa5dc6995aac2c7dc1a139e1a021927faaf73eb (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 3be1a28f58d6063258407b0751e8fb55df4749c8 Author: Jakub Jelinek <jakub@redhat.com> Date: Wed Mar 30 13:16:18 2022 +0200 Document zero width bitfield ABI changes. diff --git a/htdocs/gcc-12/changes.html b/htdocs/gcc-12/changes.html index 689feeba..f82f1a97 100644 --- a/htdocs/gcc-12/changes.html +++ b/htdocs/gcc-12/changes.html @@ -28,6 +28,31 @@ a work-in-progress.</p> <!-- .................................................................. --> <h2>Caveats</h2> <ul> + <li> + An <a name="zero_width_bitfields">ABI</a> incompatibility between C and + C++ when passing or returning by value certain aggregates containing zero + width bit-fields has been discovered on various targets. + As mentioned in <a href="https://gcc.gnu.org/PR102024">PR102024</a>, + since the <a href="https://gcc.gnu.org/PR42217">PR42217</a> fix in + GCC 4.5 the C++ front-end has been removing zero width bit-fields + from the internal representation of the aggregates after the layout of those + aggregates, but the C front-end kept them, so passing e.g. + <code>struct S { float a; int : 0; float b; }</code> or + <code>struct T { float c; int : 0; }</code> by value could differ + between C and C++. Starting with GCC 12 the C++ front-end no longer + removes those bit-fields from the internal representation and + per clarified psABI some targets have been changed, so that they + either ignore those bit-fields in the argument passing by value + decisions in both C and C++, or they always take them into account. + x86-64, ARM and AArch64 will always ignore them (so there is + a C ABI incompatibility between GCC 11 and earlier with GCC 12 or + later), PowerPC64 ELFv2 and S/390 always take them into account + (so there is a C++ ABI incompatibility, GCC 4.4 and earlier compatible + with GCC 12 or later, incompatible with GCC 4.5 through GCC 11). + RISC-V has changed the handling of these already starting with GCC 10. + GCC 12 on the above targets will report such incompatibilities as + warnings or other diagnostics unless <code>-Wno-psabi</code> is used. + </li> <li> <strong>C:</strong> Computed gotos require a pointer type now. ----------------------------------------------------------------------- Summary of changes: htdocs/gcc-12/changes.html | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) hooks/post-receive -- gcc-wwwdocs
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