[LLVMdev] Can we establish layering for the LLD libraries? Current state is a bit of a mess...

[Chandler Carruth]

On Tue, Jan 20, 2015 at 6:06 PM, Rui Ueyama <ruiu at google.com> wrote:

> On Tue, Jan 20, 2015 at 5:42 PM, Chandler Carruth <chandlerc at google.com>
> wrote:
>
>>
>> On Tue, Jan 20, 2015 at 5:35 PM, Nick Kledzik <kledzik at apple.com> wrote:
>>
>>> On Jan 19, 2015, at 6:33 PM, Chandler Carruth <chandlerc at google.com>
>>> wrote:
>>>
>>> > I wanted to go through and map out the layering of LLD's libraries
>>> today and found that it's essentially impossible. I think some serious
>>> cleanup is needed here.
>>> >
>>> > Let's start with the purely link-level dependencies encoded in the
>>> CMake build:
>>> >
>>> > Curently the Core library depends on the ReaderWriter/Native library,
>>> which links against the ReaderWriter library, which links against the Core
>>> library. This clearly cannot work. The same cycle exists with Core -> YAML
>>> -> ReaderWrite -> Core.
>>> How are you determining these cycles?   How is Core dependent on YAML?
>>> (cause that seems wrong).
>>>
>>
>> This is in the CMake build system today. You can see it with
>> CMakeLists.txt. Also you can look at Greg's patch for some of the issues
>> here.
>>
>
> It seems the dependency to lldYAML can be removed from CMakeList.txt now.
> Core doesn't actually depends on YAML.
>
> lldPasses depends on libNative, and that dependency is currently resolved
> through lldCore transitively. We should be able to remove the dependency to
> libNative from Core by fixing Pass's CMake file.
>

Cool, this makes lots of sense to me as well. We can probably fix these
minor issues quickly.

Still, it would be good to get a firm big picture that everyone agrees to
in place.


>
> If my understanding is correct, the dependencies dependencies between
> components in LLD should be like this:
>
> Config: (nothing)
> Core: Config
> Driver: Core Passes ReaderWriter
> Passes: Core ReaderWriter
> ReaderWriter: Core (and Driver?)
>
> I don't want ReaderWriter to depend on Driver, but it may be unavoidable
> because of .drectve section in PE/COFF which contains command line options.
>

Well, it *can't* depend on Driver if Driver depends on ReaderWriter.


>
> ReaderWriter should be able to be split into smaller libraries because
> there's no cross-arch dependency between sub-directories in ReaderWriter.
>

That would be nice. Can you sketch out what this would look like?


The other issue is that while the above makes sense to me, if you look at
the #include lines in these libraries, it is *very* far from the truth. How
do we fix this? In particular, the LinkingContext seems to establish a lot
of circular dependencies.
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