Re: CVS commit: src/sys/arch/m68k/m68k

[Nathanial Sloss <nathanialsloss%yahoo.com.au@localhost>]

On Thu, 10 Apr 2025 00:44:02 Izumi Tsutsui wrote:
> > Module Name:	src
> > Committed By:	nat
> > Date:		Wed Apr  9 00:04:41 UTC 2025
> > 
> > Modified Files:
> > 	src/sys/arch/m68k/m68k: fpu.c
> > 
> > Log Message:
> > Add workaround for fpu test for kernels defined with M68040.
> > 
> > This is to accomodate kernels built without the -mlcfix option passed to
> > gas(1).
> > 
> > As discussed on tech-kern - It would be remiss of me otherwize.
> 
> Do you have a certain scenario that the write-pending could happen
> just before F-line Unimplemented Exception by the fnop in fpu_probe()?

I did it to be on the safe side.  If the kernel was to be built with -mlcfix 
passed to gas(1) the nop would be inserted.  I'm unaware as to how many writes 
might be pending in the pipeline?

But if you don't deem it necessary I'll remove it.

> 
> On hp300 objdump -d GENERIC/netbsd shows:
> 
> 000146a4 <fpu_probe>:
>         struct fpframe fpframe;
>         label_t faultbuf;
>         uint8_t b;
>    146a4:       4e56 fe80       linkw %fp,#-384
>    146a8:       2f02            movel %d2,%sp@-
> 
>         nofault = (int *)&faultbuf;
>    146aa:       41ee fe80       lea %fp@(-384),%a0
>    146ae:       23c8 002d eb00  movel %a0,2deb00 <nofault>
> 
>         if (setjmp(&faultbuf)) {
>    146b4:       486e fe80       pea %fp@(-384)
>    146b8:       4eb9 0002 029c  jsr 2029c <setjmp>
>    146be:       588f            addql #4,%sp
>    146c0:       4a80            tstl %d0
>    146c2:       670a            beqs 146ce <fpu_probe+0x2a>
> 
>                 nofault = (int *)0;
>    146c4:       42b9 002d eb00  clrl 2deb00 <nofault>
>    146ca:       4280            clrl %d0
> 
>                 return FPU_NONE;
>    146cc:       6054            bras 14722 <fpu_probe+0x7e>
> 
>         }
>         __asm("fnop");
>    146ce:       f280 0000       fnop
> 
>         nofault = NULL;
>    146d2:       42b9 002d eb00  clrl 2deb00 <nofault>
> 
>         if (cputype == CPU_68060)
>    146d8:       2039 002c 5018  movel 2c5018 <cputype>,%d0
>    146de:       7203            moveq #3,%d1
>    146e0:       b280            cmpl %d0,%d1
> 
>                 return FPU_68060;
>    146e2:       6730            beqs 14714 <fpu_probe+0x70>
> 
>         if (cputype == CPU_68040)
>    146e4:       5580            subql #2,%d0
> 
>                 return FPU_68040;
>    146e6:       6730            beqs 14718 <fpu_probe+0x74>
> 
>         __asm("fsave %0@" : : "a" (&fpframe) : "memory");
>    146e8:       41ee febc       lea %fp@(-324),%a0
>    146ec:       f310            fsave %a0@
> 
>         b = fpframe.fpf_fsize;
>    146ee:       142e febd       moveb %fp@(-323),%d2
> 
>         fpframe.fpf_null = 0;
>    146f2:       42ae febc       clrl %fp@(-324)
> 
>         fpframe.fpf_idle.fpf_ccr = 0;
>    146f6:       426e fec0       clrw %fp@(-320)
> 
>         m68881_restore(&fpframe);
>    146fa:       2f08            movel %a0,%sp@-
>    146fc:       4eb9 0000 1bd6  jsr 1bd6 <m68881_restore>
>    14702:       588f            addql #4,%sp
> 
>         if (b == 0x18)
>    14704:       0c02 0018       cmpib #24,%d2
> 
>                 return FPU_68881;
>    14708:       6712            beqs 1471c <fpu_probe+0x78>
> 
>         if (b == 0x38)
>    1470a:       0c02 0038       cmpib #56,%d2
> 
>                 return FPU_68882;
>    1470e:       6710            beqs 14720 <fpu_probe+0x7c>
> 
>         return FPU_UNKNOWN;
>    14710:       7005            moveq #5,%d0
> 
>    14712:       600e            bras 14722 <fpu_probe+0x7e>
>    14714:       7004            moveq #4,%d0
>    14716:       600a            bras 14722 <fpu_probe+0x7e>
>    14718:       7003            moveq #3,%d0
>    1471a:       6006            bras 14722 <fpu_probe+0x7e>
>    1471c:       7001            moveq #1,%d0
>    1471e:       6002            bras 14722 <fpu_probe+0x7e>
>    14720:       7002            moveq #2,%d0
>    14722:       242e fe7c       movel %fp@(-388),%d2
>    14726:       4e5e            unlk %fp
>    14728:       4e75            rts
> 
> ---
> Izumi Tsutsui