[LLVMdev] [lld] supporting gnu linkonce sections in core linking

[Shankar Easwaran]

On Hexagon, clang still generates sections when constants need to be 
found in the small data section or the quick data section.

With assembly the below syntax that tries to set a constant to a 
register produces a .gnu.linkonce section.

                 r1:0 = CONST64(#200)

$ readelf -S -W main.o | grep gnu
   [ 5] .gnu.linkonce.l8.CONST_00000000000000C8 PROGBITS 00000000 000148 
000008 00  WA  0   0  8

May be MIPS also might generate these kind of sections in the field.

You might already know this, but for the current discussion, below is 
the semantics, found from a gnu bug :)

.gnu.linkonce.<datatype>.<signature>

Sometimes gcc emits the datatype for no reason, so you cannot assume 
that there is a datatype always.

Thanks

Shankar Easwaran


On 3/31/2014 6:42 PM, Rafael Espíndola wrote:
> Have you found .gnu.linkonce in the in the wild? What is producing them?
>
> On 31 March 2014 13:26, Shankar Easwaran <shankare at codeaurora.org> wrote:
>> Hi Nick, Bigcheese,
>>
>> I wanted to add support to support .gnu.linkonce sections in the resolver.
>>
>> About .gnu.linkonce sections
>> .gnu.linkonce sections were primarily present in ELF that was used in a way
>> to model COMDAT in early ELF implementations.
>>
>> We have seen usecases of .gnu.linkonce sections used in various object
>> files(mainly libc), and I think its much needed to support this style in lld
>> as well.
>>
>> a solution to support .gnu.linkonce in lld
>>
>> I was thinking of adding a typeGnuLinkOnce and special case it in the
>> Resolver.
>>
>> Differences between .gnu.linkonce and COMDAT
>> The only thing that I see a difference between gnu linkonce sections and
>> COMDAT is to raise an error when there is a similar looking section with
>> section groups.
>>
>> Do you see any better design solutions here ?
>>
>> Thanks
>>
>> Shankar Easwaran
>>
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