[PATCH] D11724: COFF: Add test for ld/section created import library

[Martell Malone via llvm-commits]

Yeah I thought the same thing would b true.
Okay I'll start working towards this then for the gendef tool.
Did you know that llvm-objdump can't dump implib sections btw ?
I started working on a patch for that.
I'll add you as a subscriber when I send in the fix


Would you be able to send me the patch you have for dll style libs ?

Thanks again for the help Rui

On Thu, Aug 6, 2015 at 5:28 PM, Rui Ueyama <ruiu at google.com> wrote:

> On Thu, Aug 6, 2015 at 9:24 AM, Martell Malone <martellmalone at gmail.com>
> wrote:
>
>> On second thought, we don't have to solve that only with the import
>>> library. You can create a (regular) COFF object containing a thunk for an
>>> aliased function, and include that object file to a .lib, no?
>>
>> Yes that seems like a good solution to this problem I might be able to
>> add something to the genlib tool to support this.
>> I might have to mockup one for yaml2obj.
>> Can we have a regular coff object in the same lib as an implib ?
>>
>
> I believe so -- the import library is just a regular ar file (.lib file)
> after all and there's no special bit or something that distinguishes import
> libraries and other .lib files, but you may want to try if in doubt. You
> can add a regular COFF file to an existing import library using lib command.
>
>
>>
>> On Thu, Aug 6, 2015 at 5:17 PM, Rui Ueyama <ruiu at google.com> wrote:
>>
>>> On second thought, we don't have to solve that only with the import
>>> library. You can create a (regular) COFF object containing a thunk for an
>>> aliased function, and include that object file to a .lib, no?
>>>
>>> On Thu, Aug 6, 2015 at 8:22 AM, Rui Ueyama <ruiu at google.com> wrote:
>>>
>>>> I don't think the short import library supports that. With that you can
>>>> undecorate names, but AFAIK you cannot define arbitrary aliases for
>>>> dllexported symbols. Does mingw-w64 heavily relies on that feature?
>>>>
>>>> On Thu, Aug 6, 2015 at 8:14 AM, Martell Malone <martellmalone at gmail.com
>>>> > wrote:
>>>>
>>>>> Before I let this slip by aswell there is one big issue with switching
>>>>> over to the implib format for mingw-w64
>>>>>
>>>>> LIBRARY "user32.dll"
>>>>> EXPORTS
>>>>> MessageBoxA == MessageBoxW
>>>>>
>>>>> dlltool objct format provides us with the option of having an alias.
>>>>> Can we do this in implib ?
>>>>>
>>>>> What the above .def means that where MessagBoxW is called it is joined
>>>>> to MessageBoxA.
>>>>>
>>>>>
>>>>> On Thu, Aug 6, 2015 at 3:58 PM, Martell Malone <
>>>>> martellmalone at gmail.com> wrote:
>>>>>
>>>>>> Yeah, I found that too and it (especially the way how it creates a
>>>>>>> gap between .idata$3 and .idata$4) looks really hacky. I also found that
>>>>>>> GNU ld has a special logic to order .idata$<n> sections.
>>>>>>> At first I thought that I could mimic GNU ld and MSVC linker to
>>>>>>> generate the .idata section, but seems like it would really mess up the DLL
>>>>>>> import table generation code. We probably should keep the existing logic
>>>>>>
>>>>>> Yeah I don't think copying gnu ld is the way to go, it is a very
>>>>>> hacky project to say the least :)
>>>>>>
>>>>>>
>>>>>> It feels to me that it makes more sense to add a new option to
>>>>>>> dlltool to generate short import libraries. It shouldn't be that hard.
>>>>>>> Martell, what do you think?
>>>>>>
>>>>>> I already wrote a replacement tool for this called genlib that will
>>>>>> go into the mingw-w64 project.
>>>>>> I want to remove mingw-w64's dependancy on binutils so that we can
>>>>>> have a clang based toolchain without binutils at all.
>>>>>> The notion of having dlltool as part of binutils made no sense in the
>>>>>> first place, It should have been part of mingw to begin with.
>>>>>> The name was chosen to correlate to on of mingw-w64's other tools
>>>>>> called gendef which creates the def files from parsing dll's.
>>>>>> I'm still finalizing the code in this and doing some tests.
>>>>>>
>>>>>> I then tried to detect dlltool-style import files and read them as if
>>>>>>> they were short import libraries, so that I can keep the existing code.
>>>>>>> That didn't work well because it's not easy to detect dlltool-style import
>>>>>>> files in a reliable manner without sacrificing performance.
>>>>>>
>>>>>> While you might not want to merge because of this into the official
>>>>>> project because of performance issues it might be something for the
>>>>>> mingw-w64 users to avail of until ld supports import style libraries.
>>>>>>
>>>>>> If you have the patch for this I'd like have a look at it if possible.
>>>>>> I'd like to try and apply this over the PECOFF for the clang 3.7
>>>>>> package in our msys2 distro.
>>>>>>
>>>>>> The issue I have is I would have to get approval to switch to using
>>>>>> genlib instead of dlltool as mingw-w64's default.
>>>>>> This would not be approved until ld supports implibs and the next
>>>>>> version of binutils released.
>>>>>> As you probably well know how things work that could take months to
>>>>>> get changed over.
>>>>>> I'd like to use your patch as a base for a temporary stop over until
>>>>>> this happens
>>>>>>
>>>>>> I'm sure the distro users of msys2 won't mind a performance hit until
>>>>>> 3.8 rather then having no support at all.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Wed, Aug 5, 2015 at 10:51 PM, Rui Ueyama <ruiu at google.com> wrote:
>>>>>>
>>>>>>> On Mon, Aug 3, 2015 at 10:36 PM, Martell Malone <
>>>>>>> martellmalone at gmail.com> wrote:
>>>>>>>
>>>>>>>> From my reading on how gnuld handles PE/COFF
>>>>>>>> It uses a linker script that describes how it lays out its idata
>>>>>>>> section.
>>>>>>>> From i386pe.x
>>>>>>>>
>>>>>>>>   .idata BLOCK(__section_alignment__) :
>>>>>>>>   {
>>>>>>>>     /* This cannot currently be handled with grouped sections.
>>>>>>>> 	See pe.em:sort_sections.  */
>>>>>>>>     SORT(*)(.idata$2)
>>>>>>>>     SORT(*)(.idata$3)
>>>>>>>>     /* These zeroes mark the end of the import list.  */
>>>>>>>>     LONG (0); LONG (0); LONG (0); LONG (0); LONG (0);
>>>>>>>>     SORT(*)(.idata$4)
>>>>>>>>     SORT(*)(.idata$5)
>>>>>>>>     SORT(*)(.idata$6)
>>>>>>>>     SORT(*)(.idata$7)
>>>>>>>>   }
>>>>>>>>
>>>>>>>>
>>>>>>> Yeah, I found that too and it (especially the way how it creates a
>>>>>>> gap between .idata$3 and .idata$4) looks really hacky. I also found that
>>>>>>> GNU ld has a special logic to order .idata$<n> sections.
>>>>>>>
>>>>>>> At first I thought that I could mimic GNU ld and MSVC linker to
>>>>>>> generate the .idata section, but seems like it would really mess up the DLL
>>>>>>> import table generation code. We probably should keep the existing logic.
>>>>>>>
>>>>>>> I then tried to detect dlltool-style import files and read them as
>>>>>>> if they were short import libraries, so that I can keep the existing code.
>>>>>>> That didn't work well because it's not easy to detect dlltool-style import
>>>>>>> files in a reliable manner without sacrificing performance.
>>>>>>>
>>>>>>> It feels to me that it makes more sense to add a new option to
>>>>>>> dlltool to generate short import libraries. It shouldn't be that hard.
>>>>>>> Martell, what do you think?
>>>>>>>
>>>>>>>> Under ld/emultempl/pep.em in binutils it describes how it converts the MS import library to its format.
>>>>>>>> see here http://github.com/bminor/binutils-gdb/blob/master/ld/emultempl/pep.em#L1625
>>>>>>>> From the code in this function and the rest of pep.em we can see how it handles it.
>>>>>>>> I'm sure this will make more sense to you however as you know what the MS format is.
>>>>>>>>
>>>>>>>> I assume the conversion will have to go the other way for us
>>>>>>>> I think the most notable thing is the use of idata7 instead of idata6 for the dll name
>>>>>>>> We could use that as a check?
>>>>>>>> Then hijack it pulling out the function names once we see this being used and insert it into the sections like a MS generated one
>>>>>>>>
>>>>>>>> You might have a much cleaner solution however. :)
>>>>>>>>
>>>>>>>> If this isn't enough insight into what you need I can do more digging.
>>>>>>>> Just ping me and let me know
>>>>>>>>
>>>>>>>>
>>>>>>>> On Tue, Aug 4, 2015 at 3:15 AM, Rui Ueyama <ruiu at google.com> wrote:
>>>>>>>>
>>>>>>>>> ruiu added a comment.
>>>>>>>>>
>>>>>>>>> Do you know anything about how GNU ld handles these import
>>>>>>>>> libraries? My
>>>>>>>>> linker is able to read it and construct .idata section, but the
>>>>>>>>> resulting
>>>>>>>>> .idata section is not going to be in correct format. If GNU linker
>>>>>>>>> is able
>>>>>>>>> to generate a correct .idata section from this type of import
>>>>>>>>> libraries,
>>>>>>>>> there must be something I'm missing in my linker.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> http://reviews.llvm.org/D11724
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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