Re: Question to struct map

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Wed, Sep 13, 2017 at 04:48:03PM +0200, Thomas-Mich Richter escreveu:
> On 09/12/2017 05:17 PM, Arnaldo Carvalho de Melo wrote:
> > Em Tue, Sep 12, 2017 at 05:04:53PM +0200, Thomas-Mich Richter escreveu:
> >> I have a question regarding struct map. 
> >> What is the purpose is the functions pointers in struct map named map_ip and unmap_ip?
> >> How do they relate the to dso the struct map is refering to?

> > A DSO has a symbol table (ELF or other kind, like the JIT ones
> > (documented in tools/perf/Documentation/jit-interface.txt) that may be
> > identity mapped or not, requiring or not use of relocation, etc.

> > The map, on the other hand, is where this DSO was loaded in memory,
> > which will be used to add to the symbol offset to do the address
> > resolution.
> 
> I think I got it now.
> The map__map_ip() function converts a symbol's virtual memory address to the
> byte offset of that symbol in the ELF file.
> 
> The map__unmap_ip() function does the opposite.
> 
> Thanks for the explanation.

You're welcome, and if I may suggest, please consider these moments as
opportunities to help people that, like you, scratch their heads in the
future about these pointers, adding comments to the struct definition
:-)

- Arnaldo