PowerPC compilation flags

[Felipe GM]

Em 2018-11-25 6:23 p.m., Segher Boessenkool escreveu:
> Hi!
>
> On Sun, Nov 25, 2018 at 05:36:38PM -0500, Felipe GM wrote:
>>> On Sun, Nov 25, 2018 at 02:42:10PM -0500, Felipe GM wrote:
>>>> Currently I am developing for a MPC5777 board, with e200z7 cores. Most
>>>> of the things are going well, but I am stuck with a problem that is
>>>> really annoying me already. I am trying to use floating point operations
>>>> on portions of my code, using the embedded hardware support. My
>>>> toolchain is GCC 6.3 (powerpc-gcc, although I have tried with 7.3 and
>>>> 8.2 too), for which I am using the following flags:
>>> *GCC 6 is no longer maintained. GCC 8 powerpc*-* does not support SPE
>>> anymore (you need to configure for powerpc*-*spe* instead; you
>>> probably want that for GCC 6 and GCC 7 as well).*
>> That is why I tried 7.3 and 8.2! Regarding powerpc-*-spe, do you mean to
>> use a different cross gcc? Or just different compilation flags?
> *It's easiest if you build for target powerpc-eabispe or whatever you 
> have. That will default -mspe etc.; and you may not even be able to 
> switch it on other configurations, at all.*
Ok, will do.
>
>>>> |ASFLAGS_BASE =-g -a32 -mbooke -me500 --fatal-warnings ARCH_FLAGS
>>>> =-mpowerpc-gpopt -mfprnd -misel -m32 -mhard-float-mabi=spe -mmfpgpr
>>>> -mfloat-gprs=single|
>>> *-mpowerpc-gpopt, -mfprnd, -mmfpgpr, and -mhard-float do not make
>>> sense for your target.*
>> I have used most of them in order to try to solve the issue. One
>> question here though. When I use -mspe (or something similar, depending
>> on the gcc version) flag, not always the floating point support is
>> provided. More than once the linker asked for the unimplemented
>> functions, similar to what I said before (__divdf3, etc).
> *Your CPU has hardware support for single precision only. You get the 
> soft float support for double precision (like that __divdf3, yes -- 
> anything "df"). This is what -mfloat-gprs=single does :-)*
That is bugging me badly. I am not trying to use double float at any 
point. Still, I am getting complaints about the linker trying to use 
them. Any clue why? That is the reason I was (am) trying to use 
-mfloat-gprs=double.
>
> *You always should link libgcc. This is the default if you link using 
> gcc, but your custom linker scripts may have other plans ;-)*
libcc is not an option, sadly. I have a very restrict (and in need of 
certification for compliance) application, so extra resources 
(libraries) are not possible.
>
>
> Segher
-- 
Ph.D. Felipe Gohring de Magalhães
Curriculum Lattes <http://lattes.cnpq.br/4701534141479314>