[LLVMdev] [LLD] support for dlltool generated libs in COFF/PECOFF

Sat Jul 25 17:54:49 PDT 2015

>
> If it's not urgent, I can take a look after finishing up x86 COFF port and
> fixing up remaining x64 bugs.

I will create a test case for it then :)

 This is not actually very unique but rather common because you usually
> always want to link against kernel32.lib which contains short import
> libraries.

Originally I thought you meant having both import types in the same lib.
You actually meant 2 separate libs one with each type. :)

I would note however that mingw doesn't use the kernel32.lib provided by MS
It has def file that was originally generated from the dll with the gendef
tool which is then given to dlltool when building the mingw crt.

If it is a mingw lib being used with visual studio however then yes this
needs to be supported
There are projects that have dll's built with mingw-w64 and that are linked
into visual studio like the vlc media player windows 8 app

On Sun, Jul 26, 2015 at 1:36 AM, Rui Ueyama <ruiu at google.com> wrote:

> On Sat, Jul 25, 2015 at 5:24 PM, Martell Malone <martellmalone at gmail.com>
> wrote:
>
>> It's doable to support dlltool-style import libraries by LLD. .idata
>>> sections in dlltool-style libraries are designed so that they will
>>> naturally construct the import descriptor table by just sorting them by
>>> section name. Supporting them is not hard.
>>
>>
>> I don't really know my way around the code base of COFF well enough todo
>> this myself.
>> If you can point me in the right direction as to what functions/sources
>> to be looking at I think I can come up with a patch.
>> If you think you can do it fairly easily I can also create a test case
>> for you if you want ?
>>
>
> If it's not urgent, I can take a look after finishing up x86 COFF port and
> fixing up remaining x64 bugs.
>
> One thing we need to do is that currently we construct the import
>>> descriptor directly from short import libraries. We don't create
>>> intermediate .idata$X sections from short import libraries. That means we
>>> cannot mix dlltool-style and short import libraries at this moment. We need
>>> to do something for that. Except that, supporting dlltool-style libraries
>>> should be straightforward.
>>
>>
>> This is a very unique scenario and I don't know of any tool that
>> generates both styles of libraries.
>> I can create one if we need it for a test case but I think this would be
>> overkill :)
>>
>
> This is not actually very unique but rather common because you usually
> always want to link against kernel32.lib which contains short import
> libraries.
>
>
>>
>> On Sat, Jul 25, 2015 at 11:29 PM, Rui Ueyama <ruiu at google.com> wrote:
>>
>>> It's doable to support dlltool-style import libraries by LLD. .idata
>>> sections in dlltool-style libraries are designed so that they will
>>> naturally construct the import descriptor table by just sorting them by
>>> section name. Supporting them is not hard.
>>>
>>> One thing we need to do is that currently we construct the import
>>> descriptor directly from short import libraries. We don't create
>>> intermediate .idata$X sections from short import libraries. That means we
>>> cannot mix dlltool-style and short import libraries at this moment. We need
>>> to do something for that. Except that, supporting dlltool-style libraries
>>> should be straightforward.
>>>
>>> On Sat, Jul 25, 2015 at 3:10 PM, Martell Malone <martellmalone at gmail.com
>>> > wrote:
>>>
>>>> Hi Rui,
>>>>
>>>> Thanks for getting back to me on this
>>>>
>>>> Do you think that you can make dlltool to generate short import
>>>>> libraries? If you can, it would be the easiest way to solve the issue.
>>>>>
>>>> On my current tests ld seems to not like libraries built with short
>>>> import libraries so this would require an ABI break in binutils.
>>>>
>>>> dlltool has support for loads of legacy targets and changing this would
>>>> also possibly break some of those targets so
>>>> Rather than working on dlltool I opted for creating a new tool for
>>>> mingw-64 to generate libs from def files using the "short import library"
>>>> Another reason for me doing this is to have a complete clang based
>>>> mingw-w64 toolchain without any gnu gcc or binutils dependencies.
>>>>
>>>> It would be ideal however if we could support what dlltool currently
>>>> produces in lld.
>>>> mingw.org toolchains will not be using the new tool I am creating and
>>>> every distribution of mingw would have to rebuild their crt's just to work
>>>> with lld.
>>>> This isn't ideal when clang is currenly used like a drop in add on for
>>>> mingw-64 toolchains.
>>>> So if it is an easy enough fix we should support this in lld
>>>> Especially when MSVC already does.
>>>>
>>>> Is there much involved with supporting this on the lld end?
>>>>
>>>> Many Thanks
>>>> Martell
>>>>
>>>> On Sat, Jul 25, 2015 at 10:38 PM, Rui Ueyama <ruiu at google.com> wrote:
>>>>
>>>>> Hi Martell,
>>>>>
>>>>> Sorry for the belated response. I missed this email.
>>>>>
>>>>> I took a quick look at the library file you have attached and noticed
>>>>> that the file consists of regular object files. LLD expects that all
>>>>> dllimported symbols are described using "short import library" (PE/COFF
>>>>> spec 7). Because I didn't test LLD with dlltool-style archive files, it's
>>>>> no surprise that it didn't work (although it should theoretically work).
>>>>>
>>>>> Do you think that you can make dlltool to generate short import
>>>>> libraries? If you can, it would be the easiest way to solve the issue.
>>>>>
>>>>> On Sat, Jul 25, 2015 at 6:23 AM, Martell Malone <
>>>>> martellmalone at gmail.com> wrote:
>>>>>
>>>>>> Hi Ivan, :)
>>>>>>
>>>>>> For testing purposes, I've managed to make the old COFF linker work
>>>>>>> with a simple test case
>>>>>>>
>>>>>> Have you got patches for this that I can look at ?
>>>>>>
>>>>>> Had to make two little changes, and link the exe manually, because
>>>>>>> the linker doesn't understand the GNU flags
>>>>>>>
>>>>>> I've solved the issue of having a GNU driver for the linker so that's
>>>>>> not an issue anymore
>>>>>> I sent in patches to the mailing list on this previously :)
>>>>>> I keep them updated over in the msys2 project btw
>>>>>>
>>>>>> By the way, even the MS linker works with the binutils generated
>>>>>>> import libraries.
>>>>>>>
>>>>>> Yes i assume binutils was based from a very old version of a MS
>>>>>> linker which did this layout at the time.
>>>>>> lld is so much newer and the MS linker has been updated to a more
>>>>>> modern layout which is why we have this issue
>>>>>>
>>>>>> Kind Regards
>>>>>> Martell
>>>>>>
>>>>>>
>>>>>> On Sat, Jul 25, 2015 at 12:43 PM, Ivan Garramona <
>>>>>> heavenandhell171 at gmail.com> wrote:
>>>>>>
>>>>>>> Hi Martell.
>>>>>>>
>>>>>>> I too was trying to make the new COFF linker recognize the libraries
>>>>>>> generated by binutils, but it wasn't resolving the DLLs, just like you
>>>>>>> described. Apparently it is not identifying the libraries as import
>>>>>>> libraries but archives.
>>>>>>>
>>>>>>> For testing purposes, i've managed to make the old COFF linker work
>>>>>>> with a simple test case. Had to make two little changes, and link the exe
>>>>>>> manually, because the linker doesn't understand the GNU flags, but it
>>>>>>> works. By the way, even the MS linker works with the binutils generated
>>>>>>> import libraries.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> LLVM Developers mailing list
>>>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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