Re: [Tinycc-devel] i386 PIC PLT optimization ?

[Fabrice Bellard]

Greg Haerr wrote:
> > 1) On i386, the PLT is built by the static linker whereas on PPC it is 
> > built dynamically by the dynamic linker. The net result is that the 
> > executables are smaller and that indirect jumps can be avoided in the 
> > PLT, so the inter DLL/EXEs calls are faster.
>
>
> Does this require paging in the entire executable for the scan, 
> or is it handled differently?  In other words, is this method likely
> to be quite a bit slower for larger executables?

It requires that the PLT is built at dll load time, but the symbols can 
be resolved lazily as it is done now. I think the slow down will be 
negligible : I expect a PLT with only 8 byte/entry (instead of 16 bytes 
currently) and the PLT creation is mostly a memset, so it is limited by 
the memory bandwidth. To give you an idea, the PLT of the glibc 2.1 
would have a size of 3.5 Kbytes.

> > Maybe implementing that in TCC could be interesting :-) A slight patch 
> > in ld.so would be needed to support that while staying compatible with 
> > standard DLLs.
>
>
> Sounds interesting, I must say.  I like the notion of later-stage dynamic
> linking.  Does this method require the symbol table, which would allow
> late-time binding by function name, or is the method using compile-time
> addresses?

Yes, it allows all that is done currently in ld.so. It is just an 
optimization.

Fabrice.