From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 24929 invoked by alias); 15 Jan 2020 18:51:49 -0000 Mailing-List: contact gcc-cvs-wwwdocs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-cvs-wwwdocs-owner@gcc.gnu.org Received: (qmail 24867 invoked by uid 10054); 15 Jan 2020 18:51:49 -0000 Date: Wed, 15 Jan 2020 18:51:00 -0000 Message-ID: <20200115185149.24864.qmail@sourceware.org> From: wilco@gcc.gnu.org To: gcc-cvs-wwwdocs@gcc.gnu.org Subject: gcc-wwwdocs branch master updated. 75712dd8e232984cc6eb7dc9aee1aeddfb54bbe7 X-Git-Refname: refs/heads/master X-Git-Reftype: branch X-Git-Oldrev: 2c7ec979b25dcea145daa4c490c12925ea9d2487 X-Git-Newrev: 75712dd8e232984cc6eb7dc9aee1aeddfb54bbe7 X-SW-Source: 2020/txt/msg00031.txt 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 75712dd8e232984cc6eb7dc9aee1aeddfb54bbe7 (commit) from 2c7ec979b25dcea145daa4c490c12925ea9d2487 (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 75712dd8e232984cc6eb7dc9aee1aeddfb54bbe7 Author: Wilco Dijkstra Date: Fri Nov 29 12:48:15 2019 +0000 Document -fcommon default change diff --git a/htdocs/gcc-10/changes.html b/htdocs/gcc-10/changes.html index 8e72bd4..5c25195 100644 --- a/htdocs/gcc-10/changes.html +++ b/htdocs/gcc-10/changes.html @@ -140,6 +140,13 @@ a work-in-progress.

  • In C2X mode, -fno-fp-int-builtin-inexact is enabled by default.
    • + +
  • GCC now defaults to -fno-common. As a result, global + variable accesses are more efficient on various targets. In C, global + variables with multiple tentative definitions now result in linker errors. + With -fcommon such definitions are silently merged during + linking. +

    • C++

    diff --git a/htdocs/gcc-10/porting_to.html b/htdocs/gcc-10/porting_to.html index 3256e8a..7d45a96 100644 --- a/htdocs/gcc-10/porting_to.html +++ b/htdocs/gcc-10/porting_to.html @@ -29,9 +29,25 @@ and provide solutions. Let us know if you have suggestions for improvements!

    Preprocessor issues

    --> - + +

    Default to -fno-common

    + +

    + A common mistake in C is omitting extern when declaring a global + variable in a header file. If the header is included by several files it + results in multiple definitions of the same variable. In previous GCC + versions this error is ignored. GCC 10 defaults to -fno-common, + which means a linker error will now be reported. + To fix this, use extern in header files when declaring global + variables, and ensure each global is defined in exactly one C file. + As a workaround, legacy C code can be compiled with -fcommon. +

    + 
    
+      int x;  // tentative definition - avoid in header files
+
+      extern int y;  // correct declaration in a header file
+

    Fortran language issues

    ----------------------------------------------------------------------- Summary of changes: htdocs/gcc-10/changes.html | 7 +++++++ htdocs/gcc-10/porting_to.html | 20 ++++++++++++++++++-- 2 files changed, 25 insertions(+), 2 deletions(-) hooks/post-receive -- gcc-wwwdocs