Re: On the cost of libraries

[Alex Larsson <alexl redhat com>]

On Sat, 1 Sep 2001, Maciej Stachowiak wrote:

> On 01Sep2001 05:09PM (-0400), Alex Larsson wrote:
> > 
> > No app will use all the symbols in the library though, and the 
> > measurements I made are worst case (all symbols are found in the last 
> > library). In reality most symbols referenced are probably in the lower 
> > layers (fan-out effect as higher level functions call lower lever), and 
> > lower level libraries are (hopefully) linked earlier. 
> > 
> 
> Actually, lower-level libraries are typically later on the link line
> so they can resolve symbols in the higher-level libraries.
> 
> > Note that this only discussed one aspect of libraries, the splitting 
> > libraries aspect. Libraries do have other costs too, such as paging in 
> > code and fixups. Most of the fixup cost can be fixed by using ELF 
> > prelinking, and page-in costs could be lowered with a grope-like tool.
> 
> So how come prelinking doesn't help with the symbol lookup cost? You
> would think a prelinked binary could know what symbol is in what
> shared library, and at what offset, assuming none of the libraries
> have changed since the prelinking was done.

Reading http://gcc.gnu.org/ml/gcc/2001-05/msg01670.html it seems that 
prelinking would probably help here yes.
 
/ Alex



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