[PATCH] [lld][core] sectionGroup support.

[Shankar Easwaran]

On 2/27/2014 4:31 PM, Michael Spencer wrote:
> On Thu, Feb 27, 2014 at 2:14 PM, Rafael Espíndola
> <rafael.espindola at gmail.com> wrote:
>>> It appears that the linker needs to deal with two namespaces, and think its
>>> best to consider the group signature separately from the other atoms. We
>>> could have an additional map in the Resolver that would just handle
>>> resolution for groups ?
>> It is probably a good idea. The part of the linker deciding to load or
>> not a group only needs to checks those symbols. The rest of the linker
>> never needs to check those symbols. Cases like the simple inline c++
>> function would just happen to be in both tables.
>>
>> Cheers,
>> Rafael
> >From what I understand, there is nothing special about signature
> symbols. They are just a way to give a name to a group and participate
> in linking as normal.
>
> Are you saying that we have a separate table that represents groups in
> addition to leaving all the symbols in the normal symbol table?
>
> Group resolution seems to only matter for comdat groups. Non-comdat
> groups just need references to properly model dead stripping.
The group signature symbols participate in symbol resolution in a 
different way,

Taking the previous example that Nick mentioned here, consider two files 
foo.o and bar.o

ELF foo.o contains:

    section 1: SHT_GROUP , name=“g1”, content=3,4(SHF_COMDAT)
    section 3:
          symbol: name=“f1”, size=30
          symbol: name=“f2”, size=16
    section 4:
          symbol: name=“d1”, size=4

ELF bar.o contains:

    section 1: SHT_GROUP , name=“g1”, content=3,4 (SHF_COMDAT)
    section 3:
          symbol: name=“f1”, size=30
          symbol: name=“f2”, size=16
    section 4:
          symbol: name=“d1”, size=4

If the link line was ld foo.o bar.o -o exec,

We would get a multiple defined error if the resolution happens if they 
are not treated as a group.

Were you seeing something else different ?

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