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

Thu Aug 6 08:22:17 PDT 2015

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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