[llvm-dev] lld: --start-lib and --end-lib

[James Y Knight via llvm-dev]

I believe the intent is that "--start-lib foo1.o foo2.o --end-lib" should
act exactly the same as if you had given it an archive "tmp.a" which
contained "foo1.o" and "foo2.o" in it.

That doesn't really seem related to gc-sections: either way, you still need
to have the normal logic to find the correct set of object files to
include, at least in order to get the correct set of global constructors
and such.

On Wed, Apr 6, 2016 at 12:07 AM, Rui Ueyama via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I hacked up a patch to support --start-lib and --end-lib in the second way.
>
> http://reviews.llvm.org/D18814
>
> In this patch, I introduced a new notion, LazyObject. That is analogous to
> Archive file type, but that works for a single object file instead of an
> archive file. This patch is +160 and -26 lines, so I can say that it is
> pretty simple.
>
> This is not directly related to --start-lib and --end-lib, but LazyObject
> may be useful for --gc-sections as well. This is the suggestion I got in
> the EuroLLVM 2016 meeting (I'm sorry but I don't remember who his name),
> but he suggested handling all object files as lazy object files for
> --gc-sections. It means by default no object files are linked. The entry
> point symbol would link one object file, and that triggers all used object
> files to be instantiated. I think this is very interesting idea because we
> don't need to do mark-sweep garbage collection to do --gc-sections;
> instead, everything will be linked only when they are needed.
>
> On Tue, Apr 5, 2016 at 7:51 PM, Rui Ueyama <ruiu at google.com> wrote:
>
>> Rafael,
>>
>> You seems to be the person who added --start-lib and --end-lib to gold
>> (*1), so I think you are the best person to ask about it. :)
>>
>> What is the intended use case of the options? Do you think we should
>> support that in LLD?
>>
>> If we want to support that, then I think we can think of two
>> implementation strategies:
>>
>>  - Link object files between --start-lib and --end-lib normally and
>> garbage collect unused sections, or
>>  - create lazy symbols for object files between --start-lib and --end-lib
>> and handle just like archive files.
>>
>> What do you think?
>>
>> *1 https://sourceware.org/ml/binutils/2010-03/msg00233.html
>>
>
>
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