Hi Martin, > I've noticed quite significant package failures caused by the revision.
How significant? Is it mostly the common mistake of forgetting extern? > Would you please consider documenting this change in porting_to.html > (and in changes.html) for GCC 10 release? Sure, I already had a patch for changes.html - I've added an initial porting_to as well: [wwwdocs] Document -fcommon default change Add an entry for the default change. Passes the W3 validator. -- diff --git a/htdocs/gcc-10/changes.html b/htdocs/gcc-10/changes.html index f0f0d312171a54afede176f06ce76f9c8abaebc4..980e4e591781d04aa888ba5988981006bd30dd1f 100644 --- a/htdocs/gcc-10/changes.html +++ b/htdocs/gcc-10/changes.html @@ -47,6 +47,13 @@ a work-in-progress.</p> <!-- .................................................................. --> <h2 id="general">General Improvements</h2> +<p>The following GCC command line options have been introduced or improved.</p> +<ul> + <li>GCC now defaults to <code>-fno-common</code>. In C, global variables with + multiple tentative definitions will result in linker errors. + Global variable accesses are also more efficient on various targets. + </li> +</ul> <p>The following built-in functions have been introduced.</p> <ul> diff --git a/htdocs/gcc-10/porting_to.html b/htdocs/gcc-10/porting_to.html new file mode 100644 index 0000000000000000000000000000000000000000..2e652f6aa4bd3259a316af0c72ab7eb96bab53b7 --- /dev/null +++ b/htdocs/gcc-10/porting_to.html @@ -0,0 +1,65 @@ +<!DOCTYPE html> +<html lang="en"> + +<head> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<title>Porting to GCC 10</title> +<link rel="stylesheet" type="text/css" href="https://gcc.gnu.org/gcc.css"; /> +</head> + +<body> +<h1>Porting to GCC 10</h1> + +<p> +The GCC 10 release series differs from previous GCC releases in +<a href="changes.html">a number of ways</a>. Some of these are a result +of bug fixing, and some old behaviors have been intentionally changed +to support new standards, or relaxed in standards-conforming ways to +facilitate compilation or run-time performance. +</p> + +<p> +Some of these changes are user visible and can cause grief when +porting to GCC 10. This document is an effort to identify common issues +and provide solutions. Let us know if you have suggestions for improvements! +</p> + + +<!-- +<h2 id="cpp">Preprocessor issues</h2> +--> + +<h2 id="c">C language issues</h2> + +<h3 id="complit">Default to <code>-fno-common</code></h3> + +<p> + A common mistake in C is omitting <code>extern</code> 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 <code>-fno-common</code>, + which means a linker error will now be reported. + To fix this, use <code>extern</code> 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 <code>-fcommon</code>. +</p> + <pre><code> + int x; // tentative definition - avoid in header files + + extern int y; // correct declaration in a header file + </code></pre> + +<!-- +<h2 id="cxx">C++ language issues</h2> +--> + +<!-- +<h2 id="fortran">Fortran language issues</h2> +--> + +<!-- +<h2 id="links">Links</h2> +--> + +</body> +</html>
