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

[Rui Ueyama via llvm-commits]

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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