[PATCH v2][MSP430] Add msp430-elfbare target

Jozef Lawrynowicz jozef.l@mittosystems.com
Wed Dec 11 12:19:00 GMT 2019


On Mon, 9 Dec 2019 15:28:25 +0000
Jozef Lawrynowicz <jozef.l@mittosystems.com> wrote:

> On Sat, 07 Dec 2019 11:40:33 -0700
> Jeff Law <law@redhat.com> wrote:
> 
> > On Fri, 2019-11-29 at 21:00 +0000, Jozef Lawrynowicz wrote:  
> > > The attached patch consolidates some configuration tweaks I
> > > previously submitted
> > > as modifications to the msp430-elf target into a new target called
> > > "msp430-elfbare" i.e. "bare-metal".
> > > 
> > > MSP430: Disable TM clone registry by default
> > >   https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00550.html
> > > MSP430: Disable __cxa_atexit
> > >   https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00552.html
> > > 
> > > The patches tweak the CRT code to achieve the smallest possible code
> > > size, 
> > > and rely on some additional generic tweaks to crtstuff.c.
> > > 
> > > I did submit these tweaks a while ago, but I didn't get any feedback,
> > > however even if they are acceptable I suspect it is too late for GCC-
> > > 10 anyway:
> > > libgcc: Dont define __do_global_dtors_aux if it will be empty
> > >   https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00417.html
> > > libgcc: Implement TARGET_LIBGCC_REMOVE_DSO_HANDLE
> > >   https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00418.html
> > > 
> > > (The second one is a bit hacky, but without some way of removing the
> > > __dso_handle declaration, we end up with 150 bytes of unnecessary
> > > code in some
> > > programs.)
> > > 
> > > So for this patch crtstuff.c was copied to the msp430 subdirectory
> > > and the
> > > changes were made to that target specific version.
> > > 
> > > Tiny program size can now be achieved by configuring gcc for msp430-
> > > elfbare.
> > > 
> > > For example in an "empty main" program which loops forever:
> > >   msp430-elfbare @ -Os:
> > >      text    data     bss     dec     hex filename
> > >        14       0       0      14       e a.out
> > >   msp430-elf @ -Os:
> > >      text    data     bss     dec     hex filename
> > >       270       6       2     278     116 a.out
> > > 
> > > Successfully regtested msp430-elfbare vs msp430-elf.
> > > 
> > > Ok to apply?
> > > 
> > > P.S. This patch relies on the -fno-exceptions multilib patch
> > > submitted here:
> > > https://gcc.gnu.org/ml/gcc-patches/2019-11/msg02523.html
> > > 
> > > P.P.S. This requires some minor configury tweaks to Newlib and GDB of
> > > the form:
> > > -  msp430*-*-elf)
> > > +  msp430-*-elf*)    
> >   
> > > I'll apply these changes if the patch is accepted.
> > > From cff4611855d838315e793d45256de5fc8eeefafe Mon Sep 17 00:00:00
> > > 2001
> > > From: Jozef Lawrynowicz <jozef.l@mittosystems.com>
> > > Date: Mon, 25 Nov 2019 19:41:05 +0000
> > > Subject: [PATCH] MSP430: Add new msp430-elfbare target
> > > 
> > > contrib/ChangeLog:
> > > 
> > > 2019-11-29  Jozef Lawrynowicz  <jozef.l@mittosystems.com>
> > > 
> > > 	* config-list.mk: Add msp430-elfbare.
> > > 
> > > gcc/ChangeLog:
> > > 
> > > 2019-11-29  Jozef Lawrynowicz  <jozef.l@mittosystems.com>
> > > 
> > > 	* config.gcc: s/msp430*-*-*/msp430-*-*.
> > > 	Handle msp430-*-elfbare.
> > > 	* config/msp430/msp430-devices.c (TARGET_SUBDIR): Define.
> > > 	(_MSPMKSTR): Define.
> > > 	(__MSPMKSTR): Define.
> > > 	(rest_of_devices_path): Use TARGET_SUBDIR value in string.
> > > 	* config/msp430/msp430.c (msp430_option_override): Error if
> > > 	-fuse-cxa-atexit is used when it has been disabled at configure
> > > time.
> > > 	* config/msp430/t-msp430: Define TARGET_SUBDIR when building
> > > 	msp430-devices.o.
> > > 	* doc/install.texi: Document msp430-*-elf and msp430-*-elfbare.
> > > 	* doc/invoke.texi: Update documentation about which path
> > > devices.csv is
> > > 	searched for.
> > > 
> > > gcc/testsuite/ChangeLog:
> > > 
> > > 2019-11-29  Jozef Lawrynowicz  <jozef.l@mittosystems.com>
> > > 
> > > 	* g++.dg/init/dso_handle1.C: Require cxa_atexit support.
> > > 	* g++.dg/init/dso_handle2.C: Likewise.
> > > 	* g++.dg/other/cxa-atexit1.C: Likewise.
> > > 	* gcc.target/msp430/msp430.exp: Update csv-using-installed.c
> > > test to
> > > 	handle msp430-elfbare configuration.
> > > 
> > > libgcc/ChangeLog:
> > > 
> > > 2019-11-29  Jozef Lawrynowicz  <jozef.l@mittosystems.com>
> > > 
> > > 	* config.host: Use t-msp430-elfbare-crtstuff Makefile fragment
> > > when GCC
> > > 	is configured for the msp430-elfbare target.
> > > 	* config/msp430/msp430-elfbare-crtstuff.c: New file.
> > > 	* config/msp430/t-msp430: Remove Makefile rules for object
> > > files
> > > 	built from crtstuff.c
> > > 	* config/msp430/t-msp430-crtstuff: New file.
> > > 	* config/msp430/t-msp430-elfbare-crtstuff: New file.
> > > 	* configure: Regenerate.
> > > 	* configure.ac: Disable TM clone registry by default for
> > > 	msp430-elfbare.    
> > OK.   I probably would have tried to avoid msp430-elfbare-crtstuff, but
> > it's not a huge wart IMHO.  
> 
> If we get the __dso_handle removal into the generic libgcc/crtstuff.c those
> changes won't be necessary.

I've attached an amended patch assuming the removal of __dso_handle
when !DEFAULT_USE_CXA_ATEXIT is approved. Differences vs the original patch are
only in libgcc/, removed the custom crtstuff implementation.

Thanks,
Jozef
> 
> Did you get a chance to look at "Add -fno-exceptions multilib" -
> https://gcc.gnu.org/ml/gcc-patches/2019-11/msg02523.html
> 
> It is the cumulative effect of these patches that gives the good code size
> results, unfortunately without them all there isn't a significant code size
> improvement.
> 
> Thanks,
> Jozef
> > 
> > Jeff  
> > >     
> >   



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