Re: ELKS memcpy_fromfs() failing. Wrong variable offsets

[Miguel Bolanos <mike@linuxlabs.com>]

I can't apply this patch as this is for dev86.. this should go to Bruce
Evans...

I will forward it to him.

Thanks

Mike

On Wed, 2004-06-02 at 02:47, Robert de Bath wrote:
> On Tue, 1 Jun 2004, Eduardo Pereira Habkost wrote:
> 
> > I am forwarding these messages to you, to check if you have any clue on
> > why this happened, and why the function worked on older versions.
> >
> > I've changed the function to use [bp-2] for the 'ds' variable, and now
> > the kernel works flawlessly.
> >
> > Do you have an explanation on how this function.off stuff works, and if
> > this have changed on older versions?
> 
> Oh my, confusion reigns.
> 
> Okay first the si and di variables are usually defined as callee saves
> unless you're compiling with the '-Mc' option.
> 
> The "memcpy_fromfs.off" stuff is generated for optimising the push/pop
> of the si and di variables. It's a reasonably recent addition so all
> accesses of si and si can be eliminated if they are unused. However,
> it's only turned on if you use '-O'.
> 
> Ie: this is working as it should.
> 
> You have highlighted a bug though, the definition some of the 'set'
> variables is actually wrong, they should have memcpy_fromfs.off added
> when it might be non-zero.
> 
> BTW: You should really be using those variables to access C arguments
> and locals, the '_memcpy_fromfs.ds' is for stack pointer relative the
> '.memcpy_fromfs.ds' is for 'bp' relative.
> 
> I can fix the bug in one of two ways; either actually add the
> 'memcpy_fromfs.off' variable to the 'set' variables or simply
> have the compiler assume that any '#asm' will use si and di.
> (The asm("...") function will not however.)
> 
> Actually I think assuming that #asm uses si/di is best because as this
> example has shown it is quite likely to be true, plus, it's the failsafe
> option.
> 
> (PS: It's also very easy to do :-) see attached. )
> 
> So do you want me to make it like it was before? :-)
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