Re: [Q] Implementation of spin_lock on i386: why "rep;nop" ?

[Jamie Lokier]

Alan Cox wrote:
> > The "rep;nop" line looks dubious, since the IA-32 programmer's manual from
> > Intel (year 2001) mentions that the behaviour of REP is undefined when it
> > is not used with string opcodes. BTW, according to the same manual, REP is
> > supposed to modify ecx, but it looks like is is not the case here... which
> > is fortunate, since ecx is never saved. :-)
> 
> rep nop is a pentium IV operation. Its retroactively after testing defined
> to be portable and ok. 

Are we sure that the value of ECX doesn't matter on a 386?  Or does it
count down doing nops ECX times on a 386?

-- Jamie