[PATCH] D12029: [lld] LinkDriver, lld-link: introduce shim.

[Martell Malone via llvm-commits]

>
> Martell's original proposal is to create a new linker driver LinkDriver,
> move everything in COFF/Driver.{cpp,h} to that, and then add GNU ld support
> to that. As a result we'd have a super driver which understands both GNU
> and link.exe options/semantics

That's not what the proposal was
It was to move the current COFF driver to lib/LinkDriver.
Then add a new gnu driver into COFF/Driver so that ELF/Driver and
COFF/Driver could share more of the same code.

The gist I sent in above however was to just add a new GNUDriver.cpp into
COFF where they can live side by side.

On Tue, Aug 18, 2015 at 1:05 AM, Rui Ueyama <ruiu at google.com> wrote:

> On Tue, Aug 18, 2015 at 2:36 AM, Saleem Abdulrasool <compnerd at compnerd.org
> > wrote:
>
>> On Monday, August 17, 2015, Rui Ueyama <ruiu at google.com> wrote:
>>
>>> On Sun, Aug 16, 2015 at 1:43 AM, Saleem Abdulrasool <
>>> compnerd at compnerd.org> wrote:
>>>
>>>> compnerd added a comment.
>>>>
>>>> If we are fine with adding custom flags to the link command line, then
>>>> aliases would be sufficient I think.  The idea is that you want to preserve
>>>> the semantics of PE/COFF (which you called the semantics of Windows).  The
>>>> difference is that the linker invocation should be similar to ld's, but
>>>> continue to provide the current semantics.  There are a few extensions that
>>>> are useful (which are compatible with the PE/COFF semantics), but the
>>>> binaries that are generated by the alternate interface are meant to run on
>>>> a Windows system, so losing the semantics of PE/COFF would be problematic.
>>>>
>>>> Just because the driver is written on/for unix, doesn't mean that the
>>>> linker should provide unix semantics.  The semantics are that of PE/COFF
>>>> because that is the target.  Its similar to how clang provides a GCC
>>>> compatible interface which can still be used to generate a proper COFF
>>>> object, even though ELF and COFF semantics are quite different.
>>>>
>>>
>>> That's true, but in most use cases, Unix driver is used for Unix and
>>> provides Unix semantics, and so are COFF. Probably more than 99 out of 100
>>> linker invocations, the default semantics are used. So defining a new
>>> driver layer for both Unix and Windows and then re-building the Unix and
>>> Windows drivers on top of it is too much. I really want something simpler.
>>>
>>> There seems not necessary to create a new abstraction layer. We can
>>> write a small Python script or something which takes Unix ld-ish command
>>> line, translate that, and invokes lld-link with the translated options,
>>> can't we?
>>>
>>
>> As long as the script is part of the same repository, I see no
>> difference.  It's just Python vs c++.  I'm not attached to any language,
>> and we already need Python to build, so having that as a runtime dependency
>> for llvm doesn't seem too big of a deal.  We should be able to document
>> Python as a runtime dependency for lld I assume?
>>
>
> They are different. IIUC, Martell's original proposal is to create a new
> linker driver LinkDriver, move everything in COFF/Driver.{cpp,h} to that,
> and then add GNU ld support to that. As a result we'd have a super driver
> which understands both GNU and link.exe options/semantics. My proposal is
> different. I don't want to add a full support for GNU ld options or
> semantics for COFF. Instead I'd write an add-on script or something (which
> can even live outside LLVM project) which is a wrapper for lld-link. Such
> wrapper will never be able to be complete since not all GNU ld features are
> supported by link.exe, but that may be able to be "good enough".
>
>
>>
>> --
>> Saleem Abdulrasool
>> compnerd (at) compnerd (dot) org
>>
>
>
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