[CFR] mge driver / elf reloc

[John-Mark Gurney]

Warner Losh wrote this message on Mon, Jul 21, 2014 at 08:46 -0600:
> 
> On Jul 20, 2014, at 5:10 PM, John-Mark Gurney <jmg at funkthat.com> wrote:
> 
> > Tim Kientzle wrote this message on Sun, Jul 20, 2014 at 15:25 -0700:
> >> 
> >> On Jul 20, 2014, at 3:05 PM, John-Mark Gurney <jmg at funkthat.com> wrote:
> >> 
> >>> Ian Lepore wrote this message on Sat, Jul 19, 2014 at 16:54 -0600:
> >>>> Sorry to take so long to reply to this, I'm trying to get caught up.  I
> >>>> see you've already committed the mge fixes.  I think the ELF alignment
> >>>> fix looks good and should also be committed.
> >>> 
> >>> So, re the elf alignment...
> >>> 
> >>> I think we should get a set of macros that handle load/stores to/from
> >>> unaligned addresses that are transparent to the caller....  I need
> >>> these for some other code I'm writing... 
> >>> 
> >>> I thought Open/Net had these available, but I can't seem to find them
> >>> right now...
> >> 
> >> $ man 9 byteorder
> >> 
> >> is most of what you want, lacking only some aliases to pick
> >> the correct macro for native byte order.
> > 
> > Um, those doesn't help if you want native endian order?
> 
> Ummm, yes they do. enc converts from native order. dec decodes to native byte

No they don't.. If you want to read a value in memory that is native
endian order to native endian order (no conversion), they cannot be
used w/o using something like below...

> order. They are more general cases than the ntoh* functions that are more traditional
> since they also work on byte streams that may not be completely aligned when
> sitting in memory. Which is what you are asking for.

So, you're saying that I now need to write code like:
#if LITTLE_ENDIAN /* or how ever this is spelled*/
	var = le32enc(foo);
#else
	var = be32enc(foo);
#endif

If I want to read a arch native endian value?  No thank you...

> > Also, only the enc/dec functions are documented to work on non-aligned
> > address, so that doesn't help in most cases?
> 
> They work on all addresses. They are even documented to work on any address:
> 
>      The be16enc(), be16dec(), be32enc(), be32dec(), be64enc(), be64dec(),
>      le16enc(), le16dec(), le32enc(), le32dec(), le64enc(), and le64dec()
>      functions encode and decode integers to/from byte strings on any align-
>      ment in big/little endian format.
> 
> So they are quite useful in general. Peeking under the covers at the implementation
> also shows they will work for any alignment, so I?m having trouble understanding
> where this objection is really coming from.

There are places where you write code such as:
	int i;
	memcpy(&i, inp, sizeof i);
	/* use i */

In order to avoid alignment faults...  None of the functions in byteorder
do NO conversion of endian, or you have to know which endian you are but
that doesn't work on MI code...

Did you read what the commited code did?

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."