[patch,avr,applied] Addendum to target/112944: Initialize FLMAP as needed

[Georg-Johann Lay <avr@gjlay.de>]

This code will link against parts of the startup code
from AVR-LibC when it is needed to init bit-field FLMAP.

Johann

--

AVR: target/112944 - Addendum: Link code to initialize NVMCTRL_CTRLB.FLMAP

For devices that see a part for the flash memory in the RAM address space,
bit-field NVMCTRL_CTRLB.FLMAP must match the value of symbol __flmap.
This is achieved by dragging in startup code from lib<mcu>.a.
The mechanism is the same like for libgcc's __do_copy_data and 
__do_clear_bss.
The code is implemented in AVR-LibC #931 and can be dragged by referencing
__do_flmap_init.

In addition to setting FLMAP, that code also sets bit FLMAPLOCK provided
symbol __flmap_lock has a non-zero value.  This protects FLMAP from future
changes.

When the __do_flmap_init code is not wanted, the symbol can be satisfied by
linking with  -Wl,--defsym,__do_flmap_init=0

gcc/
	PR target/112944
	* config/avr/gen-avr-mmcu-specs.cc (print_mcu) [have_flmap]:
	<*link_rodata_in_ram>: Spec undefs symbol __do_flmap_init
	when not linked with -mrodata-in-ram.

diff --git a/gcc/config/avr/gen-avr-mmcu-specs.cc 
b/gcc/config/avr/gen-avr-mmcu-specs.cc
index ea69145d404..bb94bea12b0 100644
--- a/gcc/config/avr/gen-avr-mmcu-specs.cc
+++ b/gcc/config/avr/gen-avr-mmcu-specs.cc
@@ -369,7 +369,10 @@ print_mcu (const avr_mcu_t *mcu, const McuInfo &mi)
      }

    // -m[no-]rodata-in-ram affects linking.  Sanity check its usage.
-  fprintf (f, "*link_rodata_in_ram:\n\t%%(check_rodata_in_ram)\n\n");
+  fprintf (f, "*link_rodata_in_ram:\n\t%%(check_rodata_in_ram)");
+  if (mi.is_device && mi.have_flmap)
+    fprintf (f, " %%{!mrodata-in-ram:-u __do_flmap_init}");
+  fprintf (f, "\n\n");

    // Specs known to GCC.