[9fans] acid - i386 floating point register issue ?

[9fans] acid - i386 floating point register issue ?

[Philip Dye]

On an i386, I am unable to get acid to properly report the values in the
floating point registers.

Could someone please explain what I am doing wrong ?

Thank you,

Philip Dye

- - - - -

Simple example:

    #include <u.h>
    #include <libc.h>
    void main ( void )
    {
      double x ;
      x = atof("3.5") ;
      print("===== main  x  = %g\n",x) ;
      exits(nil) ;
    }

Use:

    example : acid 8.out
    8.out:386 plan 9 executable

    /sys/lib/acid/port
    /sys/lib/acid/386
    acid: new()
    7118: system call       _main   SUBL    $0x48,SP
    7118: breakpoint        main+0x3        MOVL    $.string(SB),AX
    acid: asm(main)
    main 0x00001020 SUBL    $0x1c,SP
    main+0x3 0x00001023     MOVL    $.string(SB),AX
    main+0x8 0x00001028     MOVL    AX,0x0(SP)
    main+0xb 0x0000102b     CALL    atof(SB)
    main+0x10 0x00001030    FMOVDP  F0,x+0x14(SP)
    main+0x14 0x00001034    MOVL    $.string+0x4(SB),AX
    main+0x19 0x00001039    MOVL    AX,0x0(SP)
    main+0x1c 0x0000103c    FMOVD   x+0x14(SP),F0
    main+0x20 0x00001040    FMOVDP  F0,0x4(SP)
    main+0x24 0x00001044    CALL    print(SB)
    main+0x29 0x00001049    ADDL    $0x1c,SP
    main+0x2c 0x0000104c    RET
    _main 0x0000104d        SUBL    $0x48,SP
    acid: bpset(main+0x10)
    acid: cont()
    7118: breakpoint        main+0x10       FMOVDP  F0,x+0x14(SP)
    acid: fpr()
    F0       0.
    F1       0.
    F2       0.
    F3       0.
    F4       0.
    F5       0.
    F6       0.
    F7       0.
    control 0x0272
    status  0x3900
    tag     0x3fff
    ip offset       0x00001743
    cs selector     0x0023
    opcode  0xe907
    data operand offset     0xeee8
    operand selector        0x001b
    acid: print("===== ACID  F0 = ",*(F0\F),"\n")
    ===== ACID  F0 = 0

    acid: cont()
    ===== main  x  = 3.5
    7118: breakpoint        main+0x14       MOVL    $.string+0x4(SB),AX
    <stdin>:9: (error) msg: pid=7118 startstop: process exited

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Re: [9fans] acid - i386 floating point register issue ?

[Russ Cox]

> On an i386, I am unable to get acid to properly report the values in the
> floating point registers.
>
> Could someone please explain what I am doing wrong ?

You are doing nothing wrong (or at least almost nothing).
As for the rest of the system:

 - libmach has the wrong size for the 386 floating point register file.
 - libmach has the addresses of the floating point registers backward
   (i.e., F0 and F7 swapped, F1 and F6 swapped, etc.)
 - /sys/lib/acid/386's fpr() is trying to format the registers as fmt 'g',
   whatever that means, when in fact it should be using '3',
   which means the 80-bit little endian IEEE floating point.
   in fact, fpr shouldn't say a format at all, since the floating
   point registers already have the right format by default.
 - acid implements the '3' format but does not recognize it in
   acid programs (e.g., as fmt(x, '3') or x\3.

All these problems are now fixed on sources.

So your typescript should have said *(F0\3) or just *F0,
but was otherwise correct:

	% acid 8.out
	8.out:386 plan 9 executable

	/sys/lib/acid/port
	/sys/lib/acid/386
	/usr/rsc/lib/acid
	acid: new()
	1252595: system call	_main	SUBL	$0x48,SP
	1252595: breakpoint	main+0x3	MOVL	$.string(SB),AX
	acid: bpset(main+0x10)
	acid: cont()
	1252595: breakpoint	main+0x10	FMOVDP	F0,x+0x14(SP)
	acid: *F0
	3.5
	acid: fpr()
	F0	3.5
	F1	0
	F2	0
	F3	0
	F4	0
	F5	0
	F6	-183.464
	F7	0
	control	0x0272
	status	0x3900
	tag	0x3fff
	ip offset	0x0000174f
	cs selector	0x0023
	opcode	0xe907
	data operand offset	0xeee8
	operand selector	0x001b
	acid:

Russ