Re: -z combreloc

[Jakub Jelinek <jakub at redhat dot com>]

On Sat, Oct 13, 2001 at 04:14:16PM -0400, Jack Howarth wrote:
> howarth@bogus:~/debian6/zip-2.30$ LD_DEBUG=statistics ./zip 
> 08344:                   number of relocations: 256
> 08344:        number of relocations from cache: 99

This means ld.so does 355 symbol lookups, 99 of them are served from lookup
cache, the rest are looked up.

> ...after prelinking this binary I got...
> 
> howarth@bogus:~/debian6/zip-2.30$ LD_DEBUG=statistics ./zip
> 08355:                   number of relocations: 0
> 08355:        number of relocations from cache: 16

This means prelinking could be used, so no symbol lookups, just 16 conflicts
were applied (conflicts are always Rela relocs against symidx 0, so no
lookup).

> prelink: /lib/libncurses.so.5.2: Not enough room to add .dynamic entry

This means libncurses.so.5.2 was not rebuilt with recent binutils
(particularly there are no spare .dynamic section entries which prelink
needs for its work).

> under a newer binutils but all libs linked in have to
> be as well. Is this true?

Sure.

>     Lastly back to -z combreloc...is there a good way to
> benchmark any speed up gained by recompiling with that 
> option enabled in binutils? Jakub seems to have different
> output from LD_DEBUG=statistics than we do (he can get

The difference is that glibc powerpc port doesn't support HP_TIMING_*.
>From what I understand, there is mftb instruction on ppc which sets a
register to current timer value, but it is not supported on some earlier PPC
CPUs and it looks like it is 32-bit only (right?). In this case, someone
would need to hack up some way how to configure glibc which would not
support these older PPC CPUs and, assuming it is really 32-bit only and thus
overflows quickly, look at Alpha HP_TIMING_* which is limited for short time
periods too.

	Jakub