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Re: [patch,avr] PR21472: Upgrade emulation avrxmega3 so it has .rodata in flash instead of in SRAM.


On 10.05.2017 09:26, Pitchumani Sivanupandi wrote:
On Tuesday 09 May 2017 04:24 PM, Nick Clifton wrote:
Hi Georg-Johann,

On 09.05.2017 07:51, Senthil Kumar Selvaraj wrote:
I'm still not convinced we need a new emulation for this.
I would really prefer it if you two can come to an agreement about
the best way to handle this.  I am not adverse to adding a new emulation
if this is what you want, but I would be worried if this leads to an
explosion in the number of linker scripts later on.


I don't see a way how to provide a linker description file without
supplying a new emulation.
How about defining __RODATA_PM_OFFSET__ on the linker command line
and using the current avrtiny.sc script ?


diff --git a/ld/emulparams/avrxmega3.sh b/ld/emulparams/avrxmega3.sh
index abaa5b3..504c492 100644
--- a/ld/emulparams/avrxmega3.sh
+++ b/ld/emulparams/avrxmega3.sh
@@ -1,6 +1,6 @@
  ARCH=avr:103
  MACHINE=
-SCRIPT_NAME=avr
+SCRIPT_NAME=avr_rodata
I would much prefer it if you did not create a new script, but instead
added
parametrisation to the current avr and avrtiny scripts.  (In fact it
would be
even better if you could combine avr.sc and avrtiny.sc and just have
one script).

The reason for this is that the more scripts you have, the greater the
chances
of making an error or missing one out when it comes to future changes.

Take a look at the elf.sc script.  It is used by lots of different
targets, but
it is highly customizable via definitions in the target's specific
emulparams
files.

The alternative approach, which I would also consider to be
reasonable, is to have
a base avr script that defines all of the things that are consistent
between all
three proposed avr linker scripts and to include this script into
smaller,
avr-variant scripts that just defines those things that are specific
to that variant.
Kind of like how the DWARF.sc script is included into the elf.sc script.
We have tentative patch to put rodata in flash conditionally (e.g.
option flag) that
seems to be working.

gcc:
Based on flag, put rodata in new section (tentatively named
.rodataFlash). Also generates

This is not sound, IMO.  Amongst the problems this might cause are:

* Testsuite problems because of off .rodata name.

* Assembler programs might still use .rodata.

* Placement of .gnu.linkonce.r is not handled.

* The handling of .progmem appears to be broken.

Anyway, this is all GCC stuff.

You you explain why a new ld script is so bad?

Johann


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