[9fans] libmach x86 botch

[9fans] libmach x86 botch

[erik quanstrom]

it appers that either i386das and i386inst are misnamed, or they
are listed incorrectly in /sys/src/libmach/8db.c.  since at least [v7]db
follow the same pattern, i'm pretty sure the header file is wrong.
 also i believe the setting of errstr() in i386das and i386inst is incorrect.
(for a demonstration, try asm(stackaddress) on a running 386 executable.
you'll get a few bytes of unprintable garbage.)

- erik


Machdata i386mach =
{
	{0xCC, 0, 0, 0},	/* break point: INT 3 */
	1,			/* break point size */

	leswab,			/* convert short to local byte order */
	leswal,			/* convert long to local byte order */
	leswav,			/* convert vlong to local byte order */
	i386trace,		/* C traceback */
	i386frame,		/* frame finder */
	i386excep,		/* print exception */
	0,			/* breakpoint fixup */
	leieeesftos,		/* single precision float printer */
	leieeedftos,		/* double precision float printer */
	i386foll,		/* following addresses */
>>	i386inst,		/* print instruction */
>>	i386das,		/* dissembler */
	i386instlen,		/* instruction size calculation */
};

yet

/sys/include/mach.h:202,219
struct	Machdata {		/* Machine-dependent debugger support */
	uchar	bpinst[4];			/* break point instr. */
	short	bpsize;				/* size of break point instr. */

	ushort	(*swab)(ushort);		/* ushort to local byte order */
	ulong	(*swal)(ulong);			/* ulong to local byte order */
	uvlong	(*swav)(uvlong);		/* uvlong to local byte order */
	int	(*ctrace)(Map*, uvlong, uvlong, uvlong, Tracer); /* C traceback */
	uvlong	(*findframe)(Map*, uvlong, uvlong, uvlong, uvlong);/* frame finder */
	char*	(*excep)(Map*, Rgetter);	/* last exception */
	ulong	(*bpfix)(uvlong);		/* breakpoint fixup */
	int	(*sftos)(char*, int, void*);	/* single precision float */
	int	(*dftos)(char*, int, void*);	/* double precision float */
	int	(*foll)(Map*, uvlong, Rgetter, uvlong*);/* follow set */
>>	int	(*das)(Map*, uvlong, char, char*, int);	/* symbolic disassembly */
>>	int	(*hexinst)(Map*, uvlong, char*, int); 	/* hex disassembly */
	int	(*instsize)(Map*, uvlong);	/* instruction size */
};

Re: [9fans] libmach x86 botch

[erik quanstrom]

forgot to include a proposed fix

; diffy -c 8db.c
/n/dump/2011/0904/sys/src/libmach/8db.c:2060,2066 - 8db.c:2060,2066
  	USED(modifier);
  	op = mkinstr(map, &instr, pc);
  	if (op == 0) {
- 		errstr(buf, n);
+ 	//	errstr(buf, n);
  		return -1;
  	}
  	instr.curr = buf;
/n/dump/2011/0904/sys/src/libmach/8db.c:2076,2082 - 8db.c:2076,2082
  	int i;

  	if (mkinstr(map, &instr, pc) == 0) {
- 		errstr(buf, n);
+ 	//	errstr(buf, n);
  		return -1;
  	}
  	for(i = 0; i < instr.n && n > 2; i++) {

before
	; acid 1242799
	/proc/1242799/text:386 plan 9 executable
	/sys/lib/acid/port
	/sys/lib/acid/386
	acid: asm(0xdfffef8c)
	0xdfffef8c 0xdfffef8c	<stdin>:2: (error) indir: -<cr><enq>
	acid: <eot>
	echo kill > /proc/1242799/ctl
after
	; acid 1242799
	/proc/1242799/text:386 plan 9 executable
	/sys/lib/acid/port
	/sys/lib/acid/386
	acid: asm(0xdfffef8c)
	0xdfffef8c 0xdfffef8c	<stdin>:2: (error) indir: can't read instruction: can't translate address 0xdfffef8c
	acid: <eot>
	echo kill > /proc/1242799/ctl

- erik

Re: [9fans] libmach x86 botch

[Russ Cox]

asm(stackaddress) is bogus not because of libmach
but because asm is defined to disassemble from the
text file, not from memory.  Run 'whatis asm' in acid and
notice that it says @addr++ not *addr++.

[9fans] libmach x86 botch

[erik quanstrom]

On Sun Sep  4 14:34:41 EDT 2011, rsc at swtch.com wrote:
> asm(stackaddress) is bogus not because of libmach
> but because asm is defined to disassemble from the
> text file, not from memory.  Run 'whatis asm' in acid and
> notice that it says @addr++ not *addr++.

clearly.  but that's not what i'm complaining about.
i'm complaining that asm(stackaddress) accesses uninitialized
memory when printing out the error, which is therefore
exceptionally misleading.

- erik