Hi,
Add entries for the default change in changes.html and porting_to.html.
Passes the W3 validator.
Cheers,
Wilco
---
diff --git a/htdocs/gcc-10/changes.html b/htdocs/gcc-10/changes.html
index
e02966460450b7aad884b2d45190b9ecd8c7a5d8..304e1e8ccd38795104156e86b92062696fa5aa8b
100644
--- a/htdocs/gcc-10/changes.html
+++ b/htdocs/gcc-10/changes.html
@@ -102,6 +102,11 @@ a work-in-progress.</p>
<li>In C2X mode, <code>-fno-fp-int-builtin-inexact</code> is
enabled by default.</li>
</ul></li>
+
+ <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>
<h3 id="cxx">C++</h3>
diff --git a/htdocs/gcc-10/porting_to.html b/htdocs/gcc-10/porting_to.html
index
3256e8a35d00ce1352c169a1c6df6d8f120889ee..e2c7e226a83b7720fe6ed40061cdddbc27659664
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!
<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="fortran">Fortran language issues</h2>
