Date: Mon, 10 Nov 1997 03:28:07 -0600 (CST) From: Jim Bryant <jbryant@unix.tfs.net> To: sef@kithrup.com (Sean Eric Fagan) Cc: freebsd-hackers@freebsd.org Subject: Re: Newest Pentium bug (fatal) Message-ID: <199711100928.DAA07836@argus.tfs.net> In-Reply-To: <199711100741.XAA26352@kithrup.com> from Sean Eric Fagan at "Nov 9, 97 11:41:16 pm"
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In reply:
> In article <199711100650.AAA07487.kithrup.freebsd.hackers@argus.tfs.net> you write:
> >research proves that the currently discussed bug is NOT an invalid
> >opcode as he claims but in fact is an infinitely useful documented
> >instruction.
> >
> >LOCK CMPXCHG8B EDX:EAX, ECX:EBX ; crash... pp 25-72 to
> > ; 25-73 of intel's arch & prog
> > ; manual for the pentium
>
> LOCK is not a valid prefix for CMPXCHG8.
^^^^^^^^ CMPXCHG8B is the intel designation.
RTFM. p 25-73. under the heading "notes", and beginning with the
sentance "This instruction can be used with a LOCK prefix."
> %eax (and, in fact, any 32-bit register) is not a valid operand for CMPXCHG8.
p 25-72:
"Description
The CMPXCHG8B instruction compares the 64-bit value in EDX:EAX with
DEST. EDX contains the high-order 32 bits, and EAX contains the
low-order 32 bits of the 64-bit value. If they are equal, the 64-bit
value in ECX:EBX is stored into DEST. ECX contains the high-order 32
bits and EBX contains the low-order 32 bits. Otherwise, DEST is
loaded into EDX:EAX."
the only thing i question here is if i am interpreting the r/m64 byte
correctly [0x0C8].
jim
--
All opinions expressed are mine, if you | "I will not be pushed, stamped,
think otherwise, then go jump into turbid | briefed, debriefed, indexed, or
radioactive waters and yell WAHOO !!! | numbered!" - #1, "The Prisoner"
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