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

Thu Aug 6 10:13:36 PDT 2015

>
> I believe you already have a DLL and want to create an import library for
> that DLL. If so, it's too late to define an alias because exported symbols
> from the DLL are already fixed.

Yes after testing an actual importlib I found this to be true.

This must also be the reason why the syntax in dlltool is "==" and not "="
Because it is not in the spec of .def files from MS.

Thanks for clarifying that Rui

On Thu, Aug 6, 2015 at 5:57 PM, Rui Ueyama <ruiu at google.com> wrote:

> On Thu, Aug 6, 2015 at 9:51 AM, Martell Malone <martellmalone at gmail.com>
> wrote:
>
>>
>> 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?
>>
>
> That directive can be used when you are creating both DLL and import
> library.
>
> If you export a symbol from a DLL using "EXPORT foo=bar", the linker puts
> "foo" to the DLL's export table -- and no trace of "bar" is left. This
> feature is useful if you want to export a function "bar" as "foo" from a
> DLL.
>
> I think that's different from what you are trying to do. I believe you
> already have a DLL and want to create an import library for that DLL. If
> so, it's too late to define an alias because exported symbols from the DLL
> are already fixed.
>
>
>> 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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