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

Martell Malone via llvm-commits llvm-commits at lists.llvm.org
Thu Aug 6 09:51:47 PDT 2015


https://msdn.microsoft.com/en-us/library/hyx1zcd3.aspx?f=255&MSPPError=-2147217396

Apparently lib supports alias names for the symbol ?

You sure implib doesn't support this?

On Thu, Aug 6, 2015 at 5:46 PM, Martell Malone <martellmalone at gmail.com>
wrote:

> Okay I will continue with the genlib tool then.
> I will abandon this revision and create a new one once I have a library
> with the alias coff obj included.
>
> Thanks for the help
>
> On Thu, Aug 6, 2015 at 5:39 PM, Rui Ueyama <ruiu at google.com> wrote:
>
>> On Thu, Aug 6, 2015 at 9:32 AM, Martell Malone <martellmalone at gmail.com>
>> wrote:
>>
>>> 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 ?
>>>
>>
>> I don't have a patch for that. My idea was identifying dlltool-style
>> import library by the existence of ".idata$7" section (because only the GNU
>> extension uses that section) and create a ImportFile for that file, but as
>> that was too hacky, I didn't actually write code for that.
>>
>>
>>>
>>> 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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