Question to struct map

Question to struct map

[Thomas-Mich Richter]

Hi all,

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?

This is not clear to me. Must have been on vacation for too long :-).

Thanks a lot.
-- 
Thomas Richter, Dept 3303, IBM LTC Boeblingen Germany
--
Vorsitzende des Aufsichtsrats: Martina Koederitz 
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294

Re: Question to struct map

[Arnaldo Carvalho de Melo]

Em Tue, Sep 12, 2017 at 05:04:53PM +0200, Thomas-Mich Richter escreveu:
> Hi all,
> 
> 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.

- Arnaldo

> This is not clear to me. Must have been on vacation for too long :-).
> 
> Thanks a lot.
> -- 
> Thomas Richter, Dept 3303, IBM LTC Boeblingen Germany
> --
> Vorsitzende des Aufsichtsrats: Martina Koederitz 
> Geschäftsführung: Dirk Wittkopp
> Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-perf-users" in
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Re: Question to struct map

[Thomas-Mich Richter]

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:
>> Hi all,
>>
>> 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.
> 
> - Arnaldo
> 

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.
-- 
Thomas Richter, Dept 3303, IBM LTC Boeblingen Germany
--
Vorsitzende des Aufsichtsrats: Martina Koederitz 
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294

Re: Question to struct map

[Arnaldo Carvalho de Melo]

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