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From: "gjl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/112944] New: AVR: Support .rodata in Flash for Devices
 with FLMAP
Date: Sun, 10 Dec 2023 12:01:52 +0000
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X-Bugzilla-Version: 14.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112944

            Bug ID: 112944
           Summary: AVR: Support .rodata in Flash for Devices with FLMAP
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gjl at gcc dot gnu.org
  Target Milestone: ---

Devices from the AVR64* and AVR128* families (from avrxmega2 and avrxmega4)
see a 32 KiB portion of their program memory in the RAM address space.

Which 32 KiB segment is visible is determined by the bit-field
NVMCTRL_CTRLB.FLMAP.

This can be used to place .rodata in flash (it's currently located in RAM l=
ike
for all other AVR devices, except the ones from avrtiny and avrxmega3).

* The user should be able to chose the old .rodata location by means of
  a command line option like, say -mrodata-in-ram.  This is needed
  to return to the current behaviour with rodata in RAM if desired.

* The user may chose which 32 KiB block holds the rodata section.

* In all cases, the default configurations should work correctly without any
  user interventions / special code, irrespective of -m[no-]rodata-in-ram.

* The multilib structure is unchanged.

Locating .rodata in flash requires new linker description files which is
addressed by Binutils https://sourceware.org/PR31124.

The compiler part of the implementation is to:

* Add new command line options -m[no-]rodata-in-ram and -mflmap.

* Use the new / previous emulations according
  to -mmcu=3D<mcu> and-m[no-]rodata-in-ram.

* Diagnose wrong usage of -m[no-]rodata-in-ram.

* Provide built-in macros __AVR_HAVE_FLMAP__ and __AVR_RODATA_IN_RAM__.

* Don't link __do_copy_data for .rodata objects.=