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

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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.
This commit is contained in:
Georg-Johann Lay 2024-02-12 11:10:48 +01:00
parent 1e3f78dbb3
commit 525cfe1e95
1 changed files with 4 additions and 1 deletions
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5
gcc/config/avr/gen-avr-mmcu-specs.cc
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@ -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.