Re: port-mips/57680: printf("%.1f") shows wrong results on R3000mipseb

[Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>]

The following reply was made to PR port-mips/57680; it has been noted by GNATS.

From: Izumi Tsutsui <tsutsui%ceres.dti.ne.jp@localhost>
To: campbell%mumble.net@localhost
Cc: riastradh%NetBSD.org@localhost, gnats-bugs%netbsd.org@localhost, tsutsui%ceres.dti.ne.jp@localhost
Subject: Re: port-mips/57680: printf("%.1f") shows wrong results on R3000mipseb
Date: Thu, 16 Nov 2023 21:58:41 +0900

 > gas/config/tc-mips.c has the following fragment which looks like it
 > should handle this case:
  :
 > Cursory examination of the rest of tc-mips.c and mips-opc.c suggests
 > that the lwc1 instructions ought to have INSN_COPROC_MEMORY_DELAY set,
 > and both fpr_write_mask for the lwc1 and fpr_read_mask for the add.d
 > ought to include $f0/$f1.
 
 Yes, the following lines may intend to check double register accesses:
  https://github.com/NetBSD/src/blob/b720a91/external/gpl3/binutils/dist/gas/config/tc-mips.c#L4835-L4839
 ---
   /* Conservatively treat all operands to an FP_D instruction are doubles.
      (This is overly pessimistic for things like cvt.s.d.)  */
   if (FPR_SIZE != 64 && (pinfo & FP_D))
     mask |= mask << 1;
   return mask;
 ---
 
 I've also checked gas fron netbsd-7, 8, and 9
 (all of them have the similar fpr_read_mask() function),
 and it turns out binutils 2.32.2 from netbsd-7 inserts proper nops
 but 2.27 from netbsd-8 and 2.31.1 from netbsd-9 don't:
 
 ---
 % cat delay.s
         .set    reorder
 
 good:   lw      $a0,0($sp)
         add     $a1,$a0,$a0
 
 bad:    lwc1    $f1,0($sp)
         lwc1    $f0,4($sp)
         add.d   $f2,$f0,$f0
 % /s/netbsd-9/src/obj.newsmips/tooldir.NetBSD-9.3-i386/bin/mipseb--netbsd-as -v
 GNU assembler version 2.31.1 (mipseb--netbsd) using BFD version (NetBSD Binutils nb1) 2.31.1
 % /s/netbsd-9/src/obj.newsmips/tooldir.NetBSD-9.3-i386/bin/mipseb--netbsd-as -o delay9.o delay.s
 % /s/netbsd-9/src/obj.newsmips/tooldir.NetBSD-9.3-i386/bin/mipseb--netbsd-objdump -dz delay9.o
 
 delay9.o:     file format elf32-tradbigmips
 
 
 Disassembly of section .text:
 
 00000000 <good>:
    0:   8fa40000        lw      a0,0(sp)
    4:   00000000        nop
    8:   00842820        add     a1,a0,a0
 
 0000000c <bad>:
    c:   c7a10000        lwc1    $f1,0(sp)
   10:   c7a00004        lwc1    $f0,4(sp)
   14:   46200080        add.d   $f2,$f0,$f0
   18:   00000000        nop
   1c:   00000000        nop
 % /s/netbsd-8/src/obj.newsmips/tooldir.NetBSD-9.3-i386/bin/mipseb--netbsd-as -v
 GNU assembler version 2.27 (mipseb--netbsd) using BFD version (NetBSD Binutils nb1) 2.27
 % /s/netbsd-8/src/obj.newsmips/tooldir.NetBSD-9.3-i386/bin/mipseb--netbsd-as -o delay8.o delay.s
 % /s/netbsd-9/src/obj.newsmips/tooldir.NetBSD-9.3-i386/bin/mipseb--netbsd-objdump -dz delay8.o
 
 delay8.o:     file format elf32-tradbigmips
 
 
 Disassembly of section .text:
 
 00000000 <good>:
    0:   8fa40000        lw      a0,0(sp)
    4:   00000000        nop
    8:   00842820        add     a1,a0,a0
 
 0000000c <bad>:
    c:   c7a10000        lwc1    $f1,0(sp)
   10:   c7a00004        lwc1    $f0,4(sp)
   14:   46200080        add.d   $f2,$f0,$f0
   18:   00000000        nop
   1c:   00000000        nop
 % /s/netbsd-7/src/obj.newsmips/tooldir.NetBSD-9.3-i386/bin/mipseb--netbsd-as -v
 GNU assembler version 2.23.2 (mipseb--netbsd) using BFD version (NetBSD Binutils nb1) 2.23.2
 % /s/netbsd-7/src/obj.newsmips/tooldir.NetBSD-9.3-i386/bin/mipseb--netbsd-as -o delay7.o delay.s
 % /s/netbsd-9/src/obj.newsmips/tooldir.NetBSD-9.3-i386/bin/mipseb--netbsd-objdump -dz delay7.o
 
 delay7.o:     file format elf32-tradbigmips
 
 
 Disassembly of section .text:
 
 00000000 <good>:
    0:   8fa40000        lw      a0,0(sp)
    4:   00000000        nop
    8:   00842820        add     a1,a0,a0
 
 0000000c <bad>:
    c:   c7a10000        lwc1    $f1,0(sp)
   10:   c7a00004        lwc1    $f0,4(sp)
   14:   00000000        nop
   18:   46200080        add.d   $f2,$f0,$f0
   1c:   00000000        nop
 % 
 ---
 
 I'll check binutils diff between netbsd-7 and 8.
 
 ---
 Izumi Tsutsui