https://gcc.gnu.org/gcc-14/changes.html#avr
Johann
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@@ -342,7 +342,55 @@ a work-in-progress.</p>
</li>
</ul>
-<!-- <h3 id="avr">AVR</h3> -->
+<h3 id="avr">AVR</h3>
+<ul>
+ <li>On AVR64* and AVR128* devices, read-only data is now located in
program
+ memory per default and no more in RAM.
+ <ul>
+ <li>Only a 32 KiB block of program memory can be used to store
+ .rodata in that way. Which block is used can be selected by
+ defining symbol <code>__flmap</code>.
+ As an alternative, the byte address of the block can be specified
+ by symbol <code>__RODATA_FLASH_START__</code> which takes
+ precedence over <code>__flmap</code>.</li>
+ <li>The default uses the last 32 KiB block, which is also the
+ hardware default for bit field <code>NVMCTRL_CTRLB.FLMAP</code>.</li>
+ <li>When a block other than the last 32 KiB block is used to store
+ .rodata, then <code>NVMCTRL_CTRLB.FLMAP</code>
+ must be initialized accordingly by hand, or a version of
+ AVR-LibC that implements <a
+ href="https://github.com/avrdudes/avr-libc/issues/931";>#931</a>
+ must be used. The latter initializes <code>NVMCTRL_CTRLB.FLMAP</code>
+ in the startup code and according to the value
+ of <code>__flmap</code> resp.
+ <code>__RODATA_FLASH_START__</code>.</li>
+ <li>When AVR-LibC with #931 is used, then defining symbol
+ <code>__flmap_lock</code> to a non-zero value will set bit
+ <code>NVMCTRL_CTRLB.FLMAPLOCK</code>. This will protect
+ <code>NVMCTRL_CTRLB.FLMAP</code> from any further changes —
+ which would be Undefined Behaviour in C/C++.</li>
+ <li>In order to return to the old placement of read-only data in RAM,
+ the new compiler option <code>-mrodata-in-ram</code> can be used.</li>
+ <li>Read-only data is located in output section <code>.rodata</code>,
+ wheras it is part of <code>.text</code> when located in RAM.</li>
+ <li>The feature is only available when the compiler is configured
+ with a version of Binutils that implements
+ <a href="https://sourceware.org/PR31124";>PR31124</a>, which is the
+ case for Binutils v2.42 and up.</li>
+ </ul>
+ </li>
+ <li>A new compiler option <code>-m[no]-rodata-in-ram</code> has been
added.
+ The default is to locate read-only data in program memory for
devices that
+ support it, e.g. for AVR64* and AVR128* devices as explained above,
+ and for devices from the
+ <a
href="https://gcc.gnu.org/onlinedocs/gcc/AVR-Options.html#avrxmega3";>avrxmega3</a>
+ and
+ <a
href="https://gcc.gnu.org/onlinedocs/gcc/AVR-Options.html#avrtiny";>avrtiny</a>
families.
+ </li>
+ <li>The new built-in macro <code>__AVR_RODATA_IN_RAM__</code> is
supported
+ on all devices. Its defined to <code>0</code> or <code>1</code>.
+ </li>
+</ul>
<h3 id="x86">IA-32/x86-64</h3>
<ul>
