Building for an SH target without FPU

[Segher Boessenkool]

Hi!

On Wed, Mar 06, 2019 at 07:15:54PM +0100, Sébastien Michelland wrote:
> I'm having trouble building programs for a SuperH-4 target without FPU.
> 
> My current setup uses an sh4eb-nofpu-elf target which usually behaves 
> very well (much better than sh4eb-elf that uses a lot of fmov for 
> optimization), but I discovered that using a va_list causes the dreaded, 
> illegal fmov instruction to be generated.
> 
> I've looked up available options and expected -m4-nofpu to be of help, 
> however GCC does not agree with this estimation:
> 
>   sh4eb-nofpu-elf-gcc: error: command line option '-m4-nofpu' is not 
> supported by this configuration
> 
> When building I expected this target to support the option "by default". 
> I've tried building again and I found no relevant flag, even in the 
> recursive configure help.
> 
> Here is what the compiler looks like in more detail:
> 
>   Using built-in specs.
>   COLLECT_GCC=sh4eb-nofpu-elf-gcc
> 
> COLLECT_LTO_WRAPPER=/home/el/opt/sh4eb-nofpu-elf-2.32-8.3.0/libexec/gcc/sh4eb-nofpu-elf/8.3.0/lto-wrapper
>   Target: sh4eb-nofpu-elf
>   Configured with: ../gcc-8.3.0/configure 
> --prefix=/home/el/opt/sh4eb-nofpu-elf-2.32-8.3.0 
> --target=sh4eb-nofpu-elf --enable-languages=c,c++ --without-headers 
> --with-newlib --disable-nls --disable-werror --enable-libssp --enable-lto
>   Thread model: single
>   gcc version 8.3.0 (GCC)
> 
> How can I fix this setup to generate entirely FPU-free programs?

There is https://gcc.gnu.org/PR64008 which probably is relevant.

Configuring with --enable-targets=all will help.

I use this patch for sh, that may help too:

diff --git a/gcc/config/sh/sh.h b/gcc/config/sh/sh.h
index 0204872..7f126ce 100644
--- a/gcc/config/sh/sh.h
+++ b/gcc/config/sh/sh.h
@@ -124,6 +124,9 @@ extern int code_for_indirect_jump_scratch;
 #define SUPPORT_SH2A_NOFPU 1
 #endif
 #if SUPPORT_SH3
+#define SUPPORT_SH4 1
+#endif
+#if SUPPORT_SH4
 #define SUPPORT_SH4_NOFPU 1
 #endif
 #if SUPPORT_SH4_NOFPU


Segher