I believe in this case the default should be "-m4-nofpu". But not
sure, better check that. E.g. compile & link a test program (that uses
FPU-something) for the default target and for "-m4-nofpu". Then just
compare the final ELF files.
Well I tried that first and it turned out not. Here's a MWE:
#include <stdarg.h>
void f(int x, ...)
{
va_list args;
va_start(args, x);
va_end(args);
}
Now build it with two sets of options:
% sh4eb-elf-gcc -O3 -c mwe.c -o mwe-default.o
% sh4eb-elf-gcc -O3 -c mwe.c -o mwe-m4-nofpu.o -m4-nofpu
The first one is honestly a bit of a mess given the level of
optimization and the lack of any useful code. Note the fmov instructions:
00000000 <_f>:
0: 7f bc add #-68,r15
2: 61 f3 mov r15,r1
4: e2 f8 mov #-8,r2
6: 71 04 add #4,r1
8: 21 29 and r2,r1
a: 62 13 mov r1,r2
c: 72 18 add #24,r2
e: 11 58 mov.l r5,@(32,r1)
10: 72 04 add #4,r2
12: 11 69 mov.l r6,@(36,r1)
14: 63 13 mov r1,r3
16: 11 7a mov.l r7,@(40,r1)
18: 73 20 add #32,r3
1a: f2 ba fmov fr11,@r2 ; here
1c: f2 ab fmov fr10,@-r2 ; here
1e: 62 13 mov r1,r2
20: 72 10 add #16,r2
22: 72 04 add #4,r2
24: f2 9a fmov fr9,@r2 ; here
26: f2 8b fmov fr8,@-r2 ; here
28: 62 13 mov r1,r2
2a: 72 08 add #8,r2
2c: 72 04 add #4,r2
2e: f2 7a fmov fr7,@r2 ; here
30: 71 04 add #4,r1
32: f2 6b fmov fr6,@-r2 ; here
34: f1 5a fmov fr5,@r1 ; here
36: 62 f3 mov r15,r2
38: f1 4b fmov fr4,@-r1 ; here
3a: 72 30 add #48,r2
3c: 12 12 mov.l r1,@(8,r2)
3e: 71 2c add #44,r1
40: 12 11 mov.l r1,@(4,r2)
42: e1 44 mov #68,r1
44: 12 33 mov.l r3,@(12,r2)
46: 31 fc add r15,r1
48: 22 32 mov.l r3,@r2
4a: 12 14 mov.l r1,@(16,r2)
4c: 00 0b rts
4e: 7f 44 add #68,r15
But the second one is clean and FPU-free.
00000000 <_f>:
0: 2f 76 mov.l r7,@-r15
2: e1 04 mov #4,r1
4: 2f 66 mov.l r6,@-r15
6: 2f 56 mov.l r5,@-r15
8: 7f fc add #-4,r15
a: 31 fc add r15,r1
c: 2f 12 mov.l r1,@r15
e: 7f 04 add #4,r15
10: 00 0b rts
12: 7f 0c add #12,r15
The exact same code is produced regardless of optimization level.
So I guess I'll stick to -m4-nofpu. Maybe --with-multilib-list is only
used to add more architectures besides the default of the target?
For binutils, it will support all targets in the binutils (objdump etc.),
but not in ld or gas (I don't know about gdb). (You may also need
--enable-64-bit-bfd). This is quick to build and not too huge.
For GCC it only means to support all targets the backend you are building
supports; so all SuperH variants in your case.
Does that mean I could build a compiler that covers both -m3 and
-m4-nofpu ? This would be useful because I currently use both.
Sébastien
