On Tue, 14 Aug 2007, Brian Dessent wrote:
> PRC wrote:
>
> > I'm studying the ELF specfication version 1.1 recently.
> > I'm confused about the 'addend' which is used in relocation. There
> > doesn't seems to be explict descriptions about 'addend' in the
> > specification. Can somebody make detailed explainations about how to
> > calculate the value of the 'addend' when relocating an executable.
>
>
> Each architecture defines its own set of R_<arch> relocations, each with
> its own definition, so you can't really deduce anything from the generic
> spec.
True.
Btwn, your question appears to me as the purpose of addend other than as
"constant" added to get the relocated value. It manifests itself during
segment relocations - generally speaking. Incase thats not at all what
you meant, you can happily ignore the example.
For e.g :
R_386_PC32 2 word32 S + A - P
This is a pc-relative relocation. S - symbol value, A - addend, P -
PC value (location counter value)
This says the efffective value is calculated by S + A - P
Now as to A, this is computed by linker based on segment relocation
If S is 100 in data section with base address as 1000 , P is 200 in text
section with base as 0, S - P suffices if there is no data segement
relocation(or text). However if data segment gets relocated to 2000,
A will be 1000.
The example maynot be precise, but I hope you get some picture.
>
> Brian
>
--
Regards,
Anitha B
@S A N K H Y A
